 So again I have drawn this diagram to summarise what we have discussed but all this all that discussion was only qualitative discussion and we know that for any reactor design this is the performance equation and in this we know input that is the plant capacity you know what is the demand so you can decide what is the input to the plant and then we should know kinetics and we should know contacting and first we started with contacting and then found that when do you use actually batch reactors when do you use continuous reactors and in continuous reactors when do you use plug flow when do you use mixed flow I hope that you have thoroughly understood then we decided to talk about kinetics and in kinetics you have the classification of homogeneous and heterogeneous so the method of designing for homogeneous reactors or the reactions is different or heterogeneous reactors and with heterogeneous reactions is different and what we get extra at least analytically with so many examples what we have decided was that the chemical factors and physical factors both will be present in the kinetics that is in kinetic model it is not simple minus r a equal to k into c a this is a famous equation all the time in all the academic institutions because the first order reaction simplest to integrate and you know easiest to deal with mathematically and also understanding wise so that is why always we will say that we have first order reaction and we never bother about what is mass transfer what is heat transfer and all that but we had sufficient examples to justify that in heterogeneous systems it is the heat and mass transfer which may control the rate of reaction even though it is a chemical reaction chemical part may not present at all that is one example which we talked about the combustion coal gasification sorry coal combustion so in coal combustion many times it is the oxygen transfer to the coal which is rate controlling okay and the rate expression will be simply minus r a equal to k into or k g into c a g it is not k as a reaction rate constant so it is the mass transfer coefficient which you have to substitute there and then find out volume of the reactor instead of actual reaction coefficient so that is why always in heterogeneous systems we have chemical and physical systems both are coming and every time as I told you you have to visualize a model write all the steps and all the steps you have to write simple equations most of them will be mass transfer steps only one step one step will be reaction step and eliminate all the intermediate concentrations then you will get what is called a global rate of reaction now the question to be asked which I have also told you sometime earlier during discussion was how do you define first of all your rate of reaction for heterogeneous systems homogeneous systems it is straight forward and always we will say that moles converted per unit time per unit volume of the reaction mixer but here you cannot have that reaction mixer because if I have a coal combustion unit I have solids plus I have the gas so which one you really take so that is why there are various ways of defining the rates for heterogeneous systems so let us also record all of them and then whatever is convenient to you as an engineer we should be able to take that it is left to us and that is where the greatness of engineer automatically comes you have to choose the simplest one that is possible for you for the design right otherwise most difficult things if you take you know the design will be more complicated unnecessarily complicated okay so based on the unit heterogeneous rates rate of reactions are defined based on based on unit mass of solid for fluid solid reactions fluid solid reactions you know short form of reaction is rxm like action axn right so reaction so the overall rate or global rate for ith component in general can be written as dna by dt and this can be also written in terms of words moles of I reacted per mass of solid per time so this is what we widely use if you have solid and fluid this fluid can be of course either liquid or gas right and as you know I have already told you this and weight is the easiest to one to measure okay it is just simply weighing either 1 ton or 2 tons and then putting it to the reactor so but based on unit interfacial area based on unit interfacial area in 2 fluid systems that means you have gas liquid for example right liquid liquid for example okay so under those conditions or you can also say that in fluid solid systems you can also base on the fluid not on the solid right this is your choice but this one here this equation if I call this one as 1 this equation is based on the solid phase I have again fluid phase there I can also base it on fluid phase so under those conditions or fluid solid reactions based on fluid phase fluid phase how we write this one is again of course to differentiate between this and this this superscripts are given 1 by s dna by dt which is again defined as moles of i reacted per unit surface area or interfacial area and time so this is 2 ya we can also base it on based on unit volume of solid in gas solid system in gas solid system so that will be minus r i triple 5 equal to 1 by v s dna by dt again defined as moles of i reacted per volume of solid volume of solid per time so this is equation 3 then the last one there are many I am just giving only some 4 5 based on unit unit volume volume of reactor dt equal to moles of i reacted per volume of reactor so this is equation number 4 in fact we can also convert one from the other so these equations are simple evidence evidently you can just easily write this dna by dt is just nothing but w r i of 1 single prime then we also have s double prime we also have v s r i triple 5 and we also have v r ya so this is equation 5 good I think lot of discussion can be made on these equations how do you choose right for example we say that here volume of solid and here volume of reactor what is the difference Karthik do you have any difference or no difference ya void volume mainly so if it is a packed bed or fluidized bed volume of reactor means it is the fluid plus solid right or otherwise if it is only solid volume means what the true solid volume but again here there is a problem in the sense that if I have a solid porosity porous particles so now that volume also automatically taken in that solid right so we have to be very clear now how do we define and always I prefer this one because it is easiest but not it is true all the time for example if I have a slurry reactor right if I have a slurry reactor then we have three phases we have gas liquid and then solid and the general thumb rule or general convention of defining rate in a slurry reactor is moles of i converted per unit time per unit volume of bubble free slurry okay so what is that we have taken there it is the volume of liquid plus volume of solid because that is the easiest to measure for me because and if in the presence of bubbles the volume will slightly raise because that much it should occupy so then again I should find out what is the hold up of or the fraction of gas that is there in the reactor volume that is why I think most of us will not tell you the hydrodynamics of chemical reactors so that is much more important than actually mass transfer and heat transfer and chemical reactions because hydrodynamics they play very important role in heterogeneous reactor design we normally do not mention that hydrodynamics what do you mean by hydrodynamics hydrodynamics means we have hydrodynamics means we have how the two phases or three phases involved in heterogeneous systems they move okay even though we call hydro hydro generally represent water right so but in spite of that this is general name given the hydrodynamics in chemical reactors and where you have to predict what is the fraction of each phase in the reactor volume right that means if when I am operating with certain gas certain liquid and solids are constant for example if you take then depending on gas flow rate and liquid flow rate the reactor occupies you know certain volume of gas or volume of liquid solid is constant anyway right so depending on these two flow rates how this fractions change and those are very important because if I have a reaction I am just imagining that I have A plus B plus C in a three phase reactor going to product right so what I told here is one mole one mole one mole but in the actual reactor because of hydrodynamic conditions gas may not be one mole it may be point not one moles because hold up is so low then naturally that becomes a rate controlling step and you will not have you will definitely not get more conversions right point not one percent if you take you know so that is the reason why we should first know the hydrodynamic conditions in each individual reactor not only that not only the fractions hydrodynamics will give you not only the hold ups we also should have flow regimes you know when I have two phases solid of course is there as a batch system and two phases are flowing so if I have counter current system then it is not possible to go for very high values of liquid and very high values of gas why flooding all counter current systems will flood even though we know that counter current system is much more efficient than co current system we know that but in spite of that there is a limitation on the throughput side operation side so that is why that flow regimes will tell me whether what is the maximum gas velocity or maximum liquid velocity which I can take this is what first you should have done in your mass transfer course also particularly for packet beds right gas absorption or even distillation the first thing you do is go to that graph given in tri ball and then try to read what is the maximum gas for a given liquid flow rate that automatically fixes your maximum throughput but how do you find out this for a new column you have to do you have to do the hydrodynamics so that is why all my research is not actual reactions even though I teach reaction engineering most of the time this is the first step hydrodynamics I have never come out of that even after that years still doing hydrodynamics only okay so in every system you should be able to find out what are the flow regimes what are the hold ups and what are the phase velocities what do you mean by what are the phase velocities if it is a fluidized bed okay it may be three phase fluidized bed that means three phases are going solid is anyway constant the volume is is a batch system then gas and liquid both we send right but the solids have to fluidize I hope all of you know what is fluidization right fluidization is the phenomena where the solid particles are kept under suspension so that they behave like a fluid okay so that is why we called fluidization that means imparting imparting the properties of fluids for solid particles otherwise solids are immobile they would not move right so but I should know what is that minimum velocity that is required for this fluidization to take place if I do not know that what is happening I want to use fluidized bed but most of the time it is under packing conditions packet bed conditions so that is why the phase velocities and the other extreme is that I may use very high velocity because I do not know anything about hydrodynamics very high gas velocity or very high liquid velocity and these velocities have already they may be more than the terminal velocities of the particles so if you are not careful or even if you careful and then put on the top of the reactor mesh all the particles will go that is inverse packet bed because the packing will go and stick to the top because because you put a mesh they are not able to go out if you do not put the mesh there is no there will not be any particles inside the reactor at all so that is why that fixes the boundaries the phase velocities that is why these are the factors normally apart from that the pressure drops this is also very important so what is the total pressure drop across my column so that that is the minimum thing which I have to provide through the pump otherwise you cannot push the liquids from the bottom or from the top so the pressure drop so these are the general things in hydrodynamics what we have to study and all heterogeneous systems this is the first study in fact that is why beautifully we have a course called multi phase systems and without multi phase there is no chemical engineering okay single phase systems are very very very very very few so minimum you will have 2 and why even a distillation column you take right so there are hold up correlations I do not know whether you have used them but the beauty using the beauty of using macabre theory method is not to consider all these things it is a wonderful design I think really we have to appreciate as chemical engineers first of all I always think that how do these people get that idea that you are designing a mass transfer column without talking about any mass transfer coefficient you do not use a single mass transfer equation right you simply go for thermodynamics take VLE data draw okay and then go for material energy balance which you studied in your first semester right then balance you will get the operating lines and in between this equilibrium line and operating line chick chick chick that is all 10 chicks means 10 plates 15 chicks means 15 plates right and after that we have a nice fellow called Murphy and go to Murphy and take Murphy efficiency may be 80 percent 60 percent 70 percent depending on the system okay what do you mean by depending on the system when do you take 50 percent when do you take 80 percent Murphy efficiency have you thought normally we tell you in the class take 50 percent you take 50 percent without questioning okay and sometimes we take 80 percent you take only 80 percent but you never question all of you are very good students yeah contacting time what do you expect you know in that design in that in the yeah but in that method on each plate what is that we are assuming theoretically equilibrium and you know what is the time required for equilibrium theoretical infinity so that means you can never come back again if you go to infinity right infinity time if you go again where are you I think we will not be there so that is the reason why practically we have to wait for some time right so actually that is a rate process converted into equilibrium process but the actual rate process what we are using rate means you know mass transfer rate is the other approach we have two approaches equilibrium approach the other one is the rate approach and generally if you have a packed bed you use mass transfer equations that is why two films you draw and then you write the mass transfer equation okay and then how the concentrations are changing how the mass transfer coefficient at each and every height along the column all that you integrate and then you of course again as an engineer you will again simplify that in terms of NTU HTU and all that because easy to convert for the design so these two approaches but there also you need the this phase hold ups you need flow regimes you need phase velocities and definitely you need pressure drop right and pressure drop luckily we have only one equation for packed beds we have to thank Ergun and the story is that I know I do not know whether really we have to believe this or not someone was telling me that story some not Cambridge University some University from UK it seems when he submitted his thesis on the pressure drop of you know pressure drop through packed beds he was failed because there is no contribution from him you know for PhD you need some contribution some totally new knowledge which has not been existing till then right but I think people thought examiners thought at that time that you know there is no sufficient newness in this pressure drop of the fluids through the packed beds he was failed in the examination but you know that failure only we have been even now using even after 70 60 years that is the only equation what what else you have all other equations are only some extension delta X delta X extension of that same equation the same thing even it is in monodes equation or make less mental equation one of those I do not remember now one of those papers have been rejected saying that this paper is not worth publishing you see in the history of this research and then you know development of concepts some things which we have thrown out that it is a useless concept later that is the only concept that was valid okay so all beautiful histories are there if you just try to understand how chemical engineering developed or any process developed good so that is why hydrodynamics are very very important for heterogeneous system good so and most of the time if you look at the at the rate equations given in the textbooks if it is a packed bed many times this is the one that is used if it is a slurry reactor many times that is used is based on volume of bubble free slurry that is what and if it is gas liquid system you do not have any choice except that you have to go for interfacial area and you see the most difficult thing in chemical engineering is finding out interfacial area for surface area for solids it is fine solids also has interfacial area but I can easily find out solids interfacial area if I know the particle size even particle size distribution so I will go to sieving which you learnt in your may be fourth semester fifth semester mechanical operations and then you have various sieves may be between these sieves each time you will have may be 10 percent 20 percent 40 percent like that and in each category within that you know what is the particle size average size find out that interfacial area surface area so like that all surface areas you can add up I am talking about just external surface area sieve gives you only external surface area because what I am trying to say is particles are not changing with time even in the packed bed so you can easily find out what is the interfacial area based on external surface area alone but you also have fairly very good techniques to find out what is the internal surface area for the porous particles what are the methods BET is one method and you also have mercury porous meters but BET will give you to certain range of pores and mercury also mercury porous meter also will give you certain other range of pores but all these pores you have to add and then find out what is the total surface area and that will be very useful for catalytic reactions but advantage there is those particles are not changing with time unless you have deactivation okay so that is why I am very fairly confident about that but the systems with gas liquid and also liquid liquid very difficult because you have the in liquid liquid system droplets one is continuous phase other one is the dispersed phase in the dispersed phase you have the small bubbles large bubbles and unfortunately large bubbles will become we will break and then become small bubbles and small bubbles will coalesce and then become large bubbles we do not know how to really predict what is happening throughout the system in the process that is why that is one of the most difficult parts in evaluation in evaluating the interfacial area and much worse is your bubbles also right that is why if you are able to design a system where you can beautifully produce only single bubbles or single droplets of uniform size then this very very accurate surface area is very very accurate because I have only I have to measure only one bubble size all bubbles are same afterwards so then simply multiply by number of bubbles and then each bubble what is the surface area that is why I like this screen saver there is one screen saver with bubbles I think in windows 7 or so so I mean I always put that wherever I go I have computer in house computer here wherever I see I have that possibility I will push though that screen saver because thinking that how beautiful it would be if I am able to produce that kind of highly beautiful spherical particles on the screen okay but the same thing if I can extend to my research area also that will be wonderful and I am doing some work on the inverse fluidized bed is lost may be 10-12 years so there we have observed this kind of uniform bubbles okay this inverse fluidized bed is used for wastewater treatment the liquid is sent from the top because these are the lighter particles that is why it is called inverse fluidized bed the particles if you just put in batch of liquid this will float to the top because they are lighter particles lighter than water so now to fluidize that I have to push from the top right and that pushing liquid is in simple terms it is the wastewater right and then this is a biological process where the microorganisms require oxygen so that is why I now send my air from the bottom okay it is 3 phases counter current system and why should I use an inverse fluidized bed we cannot use a normal fluidized bed yes it can be used the advantage of inverse fluidized bed is the particles are lighter particles so they have less inertia less inertia so due to this less inertia the particles can easily move okay or rotate when they are rotating they will destroy the film liquid film surrounding the particle what will happen now yeah mass transfer fresh area generates and then mass transfer is maximum so when mass transfer is maximum and particularly if mass transfer is controlled and for even biological processes mass transfer may be controlled oxygen supply for example that is why I told you already wastewater treatment open ponds right very big large scale very very large area you have to use the reason is that you do not have an efficient way of mass transfer to each and every microorganism so they do not work they will die of suffocation so that is why you have to use largest size to compensate for your final production rate so in this inverse fluidized bed it is not right because it is very efficient system where this will break in fact it was found that may be 1.5 to 2.5 times the mass transfer coefficient can increase number wise you may think it is very small so that means it is directly proportional and mass transfer coefficient doubles means area will be half area of the system what you are using so that way it is very advantageous there what we have observed was when the bubbles are coming and the particles are expanding down right and in between those particles the bubble size is almost uniform because the gas has to go through the bubbles I mean through the particles and the liquid is trying to expand the particles so depending on the density hold up of the solids if the hold up of solids is more almost like a packed bed I guarantee almost uniform bubbles through and definitely I know that how much mass transfer you know oxygen going to the liquid then that liquid goes to the surface of solid on the surface we have the microorganisms so microorganisms happily take the nutrients or the food from the wastewater and also breathe the dissolved oxygen then happily it will work it will reproduce because good environment for it because it is good food and good you know oxygen amount of oxygen so that is why what is the next one that is left in the nature reproduction so that is why more and more microorganisms also are developed or produced then you will have very efficient process there also we are studying all the time even now we do not have correct equations for minimum fluidization velocity for example this phase velocities we do not have an equation for pressure drop only recently we have developed that and I think I have to publish that I think we were the first people to say to give a pressure drop equation till now in the world that not had published only student recently submitted his thesis there is no equation for pressure drop in a inverse fluidized bed and of course the flow regimes flow regimes we have not had done but there are just only one or two papers for studying flow regimes and of course hold up some many people studied and beauty there is if I do my experiments it is not telling with other experiments so we have some six seven others we have published this hold ups everyone has a different correlation I do not know what to normalize now in fact my next attempt is that you know what is that why different people have given different correlations I am telling all these even in this course because that is what the information you need if you design a new system it is not existing then you have to develop all these hold up correlations flow regime map and also phase velocities pressure drop correlations all that otherwise you cannot design the equation I mean you cannot design the reactor right okay so this is what is the what are the general difficulties when you go for kinetics and we decided now we have to concentrate or throughout the semester we will talk most of the time on the kinetics part of heterogeneous systems and the first one what we take in this is gas solid non catalytic reactions okay then we will take gas solid catalytic reactions then we take the fluidized fluidized beds will come under gas solid catalytic reactions then we will take slurry reactor right so in gas solid non catalytic reactors we will try to design packed beds and also fluidized beds and in catalytic reactions also packed beds and fluidized beds and in slurry reactor of course there is only one slurry reactor right so this is the overall picture first finding out the kinetics that means kinetic models have to be developed and then we have to use that information in the design of the reactor for either packed bed or fluidized bed or moving bed or rotary kiln procedure is same but we cannot do everything in this course so at least these important things and very frequently used reactors are these packed beds fluidized beds slurry reactors in the industry moving beds also are used but I think very difficult to control moving bed rotary kilns are again very easy and the design also very easy I think you know even though we do not have to design that but it is very easy to design I will let you know when the time comes and rotary kilns are mainly used for gas solid non catalytic reactions of course yes solid solid reactions and non catalytic reactions like gasification okay so people use the rotating kilns okay good so that is the overall picture and now we will go to gas solid non catalytic reactions and first to know in gas solid non catalytic reaction is what kind of reaction first of all you have you may be wondering what you mean by what kind of reactions okay so example I can say simply tell you if I have iron ore reduction Fe 2 O 3 plus H 2 giving me Fe plus H 2 O okay that reaction is quite different that is also non catalytic reaction gas solid when I compared that with gasification reaction or combustion reaction what is happening is here coal plus C plus O 2 giving me C O 2 but there I have the solid product at the end in iron ore reduction whereas here I do not have anything because particle will disappear you may have ash and there are coals where ash is almost negligible 5 percent ash 10 percent ash so then there is nothing in the reactor then how do you design the reactor you do not need any reactor which means so that is why and also there are some beautiful reactions non catalytic reaction for example we are using our computers and all that very happily right and silica is one of the things which chips to make and you know how difficult it is to produce that pure form of silica and one reaction that is used is silane that also I will write S i H 4 going to S i plus 2 H 2 so that means actually it is a gas and after reaction I see the solid product wonderful design and I guarantee you if you develop a process now there are many companies that are trying to do in the world you will become a millionaire why millionaire you can become a billionaire if you are able to develop that process of producing pure silica in India no one is producing we are only importing and of course one good thing with us is we do not design chips okay so that is why you do not have to import that much silica someone else is doing that so that is why very big companies like union carbide now union carbide of course is joined with someone else I think you know yeah those people are still trying to get the maximum there are some processes but which are very costly which are difficult not only costly process wise difficult that means slight change in the process conditions you do not get silica so how do you design a robust process and then try to get the purest form of silica there are still many many reactions like that and another wonderful non catalytic reaction I can tell you ceramics Chinese have made this technique long time back you know beautiful you know Chinese porcelain is one of the wonderful qualities right but we do not have that kind of quality that they are doing even now by earth rather than using science because the solid solid reaction is also not that easy to understand and then try to use the scientific information for the design of tea cups or coffee cups right but you see the greatest in the art because art has been developed over the hundreds or thousands of years that is why they became experts but unfortunate thing is only that family is expert in that they cannot communicate with anyone else but if I have a scientific method whoever understands science happily they can use that information that is the difference between art and science because suddenly I cannot become a painter only it is possible for M F Hussain may be afterwards his children I do not know anyone is his children really painting or not because genes will definitely work to some extent okay all of us know that doctors becoming doctors tennis players becoming tennis players you know the family cricket players and maximum number you can say that movie actors becoming movie actors that is the maximum fraction so these are all always a little bit genes and then environment right because from morning to evening in a movie actors house always they discuss about movie that is good this is bad I fought with 100 people I fought with 10 people today so I am on the screen so all that they will be discussing so slowly the genes also try to change you know through the environment saying that okay finally I have to also become like that right so that is why this first identifying what kind of reactions we have is very important right so now that is why let us just list out some industrially important reactions first I have to take non-catalytic or okay kinetic models for non-catalytic for non-catalytic reactions so let us say some important important okay I can write industrially reactions okay we will divide this into different types and I will say that first I have type A reactions where we have solid plus fluid going to again solid plus fluid I think just now I have told you one example what is that yeah so this is Fe3O4 solid plus H2 gas giving me Fe solid plus H2O gas okay so I have to balance this F3 so then this is for yeah then this is for yeah that is one reaction the other reaction is of course roasting of zinc zinc ore ZNS solid plus O2 gas giving me ZNO solid plus SO2 gas so again if I balance this is 2 this is 2 this is 2 this is 3 I think hopefully I can write 2 4 6 yeah okay so that is the reaction there are many but I just want to give you only one or two so that you are comfortable this is type A and type B we have solid plus fluid giving me solid I have my favorite reaction here that is calcium oxide CAO solid plus half O2 gas plus SO2 gas giving me CA calcium sulphate and this is one of the famous equations for removing sulphur from flue gases you know thermal power plants and all that you have so from there using this reaction you know sending this amount of oxygen this amount of if you have this amount of SO2 this amount of CAO you can always this is what one of the very one of the methods very widely used in fluidized bed combustion you know in fluidized bed combustion what do they do fluidized bed combustion is very famous particularly for sulphur coals and high ash coals okay fluidized bed combustion okay and it is a fluidized bed where along with coal they also put calcium carbonate particles calcium carbonate is nothing but our Taj Mahal okay yeah they do not put Taj Mahal I think you know calcium carbonate particles they just put what happens is this calcination step is the first one calcium carbonate is CACO3 and if you expose that to very high temperatures then you will have CAO plus CO2 that is instantaneous reaction that is why you simply throw calcium carbonate particles in the fluidized bed chamber then first reaction is instantaneous it becomes CAO at any time I will see CAO so now this is another example for me to tell you rate controlling step which one is the rate controlling step either this one or the first one where calcination CACO3 becoming to CAO this one is the rate controlling step because that is instantaneous that means any time I see that I have calcium oxide that means because calcium carbonate has been converted to calcium oxide right so then this reaction takes place and you know there are many beautiful things about this there are at least may be 100 papers on this how this reaction is taking place with CAO okay so what is the beauty in these reactions is that this one this calcium sulphate has more molar volume than calcium oxide molar volume so that means the volume of particle will increase during the reaction and that is bad for the reaction because the calcium carbonate when it is becoming calcium oxide you have lot of pores lot of pores means like our like our bread you know what you will do you take okay more fluffy the bed is the more porosity in the bread just imagine you know without porosity you are trying to eat bread that becomes roti okay yeah it is not bread so that is why the greatness of this modern bread and all that to make lot of porosity but still you know it is nicely edible right so that is why immediately that it forms large pores I mean pores inside the particle then calcium sorry then SO2 will try to diffuse into that so if I just look at one pore this pore may be something like this okay one pore just one pore and I have some thickness of this pore and SO2 is trying to diffuse there this is SO2 of course with O2 and all that right so then what happens because here I have more diffusion by diffusion if I draw the profile the concentration SO2 O2 profile will decrease because of the resistance very small pores so naturally that decrease in concentration will come and you have the maximum concentration at the mouth therefore rate of reaction is more faster so when the rate of reaction is more here calcium sulphate forming will be more and that forms something like this this is the calcium sulphate you see now this pore actually now this is the mouth of the pore all this is solid so after some time what happens is this SO2 or O2 cannot go inside this blocks but still I have large amount of calcium oxide that is left inside the pore this all waste that means if I visualize one single particle if this is the particle size where the reaction is practically taking place only this one that is where you have calcium sulphate and all this is waste for me that means I am generating now lot of solid waste or not good quality of calcium sulphate because outside calcium sulphate inside actually I have calcium oxide that is why in Germany I saw one company Lurgy what they do is they spray water on that after some time of reaction they spray water on that and you can also do not only in combustion you can do this even outside you know flue gases can be taken out first and then have the calcium same reaction in the separate reactor that also they can do so there they spray water what do you think will happen if they spray water because we know the solubility of calcium sulphate that is very high in water but it will just absorb water and then that water will go and touch the calcium oxide this is CAO and you know the reaction between CAO and water what kind of reaction exothermic or endothermic but is it exothermic reaction or endothermic reaction highly exothermic reaction I do not know most of you would have not put this white wash in your house you try to buy calcium hydroxide you know calcium oxide and then make as calcium hydroxide and then try to bubbles actually it seems that is one of the punishments that is given to on the olden days one of the punishment that is given to I mean thieves and or murderers by kings you know what they do they will ask the person to stay like this put all calcium oxide around them and put water he also becomes all his bones become calcium he just you know life burnt that really I mean it was regarded in some you know because ruthless people at that time kings probably we need them now otherwise things may not work here in our country okay so that is why that exothermic heat is used to burn to burn the body right so what happens is when they when so much heat is generated inside and the remaining some of the amount of water which is going that evaporates so when it is evaporated it has to come out what does that do it breaks and come out so when it breaks and comes out all this area is again inside exposed to calcium oxide I mean sorry for SO2 and O2 for reaction to take place you see these are very beautiful simple technique which we never normally appreciate that is why tremendous amount of good innovations are in industry but they never record because by recording if someone steals like that movie inception or other things okay so then they will make millions other people also make millions this this company will go that is why everything is kept under a secret but tremendous technology in fact this silane SI from silane is one of the really strongly guarded secrets by the industries because you know without computers nowadays we cannot live right that has become food for us 2 or 3 days if you do not have computer I mean if you do not have food it is okay but one day if you do not see your e-mails entire world will crumble so that or otherwise if you do not tweak tweak a tweeter tweeter you cannot sleep okay or if you do not chat with your friends whatever you eat also it will not get digested so that is why so many things are there you know with computers so the demand for silica is maximum right so I think someone who is interested in technology can always go for this production of silica pure silica as chemical engineers if atleast one of you can do that I think it is excellent you will become billionaire and then you can come to IIT as chairman board of governors okay that is what normally you know very high level industrialists or academicians are given as chairman board of governors to direct us what we have to do in IITs okay anyway so this is the information about the okay type 2 yeah the difference between type A and type 2 reactions and this is one of the famous reactions and another there are many for example rusting of iron that everyday we see but we never appreciate that one as one of the non catalytic reactions right okay so this is FeO solid plus O2 gas giving us FeO FeO solid again you know this is I mean for me everything is exciting I say I do not know for you how many things are really exciting now everyday we see here and the rust also will not form that nicely all the time sometimes if you see your cycle you will see that you know the some material will come off as flakes and somewhere it will beautifully deposit as grains why we never discuss you never even observe huh yeah that is what that is a chemical reaction okay that is what my interest is different forms of react corrosion is not simply it is a non catalytic reaction but of course in IIT Madras what is happening now is any cycle whatever is by you it is stolen right I think in hostels many cycles are stolen that is what people are telling okay this is balance 2 no this is 2 correct yeah so like that we can list out even type A type B then there are 2 more or 3 more