 So let's look at one of the simpler types of ethanol. We know that combustion is a particular type of chemical reaction and this chemical reaction is one that requires a fuel which will be the alcohol in this case. It also requires oxygen and in fact the amount and availability of oxygen often affects the products of this reaction. And it's also going to be producing energy. The purpose of combustion reactions is for the generation of energy. And so as a result of that we have an exothermic process where this reaction is going to release energy and we can use that released energy which will appear in the form of heat to heat water. So we can increase the temperature of water, look at the amount of water that we have and the degree to which that temperature rises and then work towards a change in enthalpy value and hopefully a molar enthalpy value for our combustion reactions for different alcohols. It's important that you identify the alcohols that you're using for these reactions, that you also identify the reaction that's involved. Importantly we're going to be assuming for each of these that we have complete combustion that may or may not be a reasonable assumption and one of the things that you would want to consider when you're looking at the reliability and validity of your results, how many times you're going to repeat this experiment in terms of reliability and often with each of these fuels there it will be a theoretical value for the molar enthalpy of combustion which you can actually compare with your experimental values to then make some comments about the relative validity of your methods. So make sure that you have the formula for each of the alcohols that you're using, assume complete combustion and then that will give you the products of carbon dioxide and water and from there you should be able to balance the equations. So this is a revisiting of the MCAT equation. So in this case we know that the heat flow that is going to occur from the reaction through into the water is going to be found by the formula MC delta T. We know that M will be the mass of the water, the temperature rise of the water is delta T and the C is the specific heat. So one of the things that's really important about this is that when you use MCAT these must all relate to the same substance. For the example that we're looking at this is going to be in our case water. One of the most common errors that students make is to use the value that they have for the mass of the alcohol in this position here and that is going to need a great big red cross. We do not put the alcohol in the mass part of this equation because we have to make sure that when we are looking at using this particular equation that every single one of these variables relates to the same substance. That is if we're talking about water it's going to be mass of water, it's going to be specific heat of water and it's also going to be the change in the temperature of the water and that is why you need to make sure that you separate two stages of calculations here. The other thing that I've just changed slightly is that on most of the data sheets you'll actually find that the value for the specific heat of water is actually given in kilograms rather than in grams. So joules per kilogram per Kelvin and that means that the value here is often listed as 4.18 times 10 to the 3. When you convert from grams to kilograms you're going to divide by 1000 so therefore our value for the specific heat is 1000 times bigger and those two things will cancel each other out. I think most of the time the quantities of water that you're going to be using to heat are going to be in mills and therefore they're easiest transferred into grams because we know that for water one mill of water weighs one gram and therefore 100 mills will be equivalent to 100 grams and that's the value that we can put into our equation. It may also because of the size of the quantities that we tend to get with these sorts of calculations that you change joules into kilojoules just to make the numbers a little bit easier to deal with.