 What I'm going to do today is really to introduce a general idea of reactor transfer equation and the overview of it. This equation that I put here is we call mass conservation equation for chemical species in aqueous phase, for one of the representative species. I don't expect you to know every term, details of every term in this equation, because we will be talking more about this each term later. But this is really to give you a general idea and overview before we start about everything. And the importance of this is that we run these reactor transfer code, and there are a lot of build-up architecture behind the coding term of what they solve. And it's always a good idea to know some of these, like what they solve and what are the things behind these codes. So what I will do today is really talking through each of these terms and talking about the physical meaning of each term so that you get a general idea what are they really for. So the first term is we call mass conservation term. It's called mass accumulation rate. And it should have the units of more per length cube, which is volume of pros media per time, whatever time you pick. But all the term has to be consistent, have the same length and the time units. So this equation really says mass accumulation rate depends on several different processes. So the first term is the rate itself, and then overall rate. The second term what we call dispersive and diffusive transport. So you think about how a chemical species in water has a change over time, which is this. So some of these rate coming from, for example, the chemical species go to get, like, there's different concentration in different locations. For example, you think about a dye putting a cup of water and they tend to, over time, they tend to have the same color everywhere. So this is one of the driving forces in terms we call just diffusive or dispersive transport. And they should have same unit as the first term. Every term has the same units. So that's the second term. And then the third term is we call diffusive transport. And this is a process where, for example, you think about rivers, right? And the chemical species will flow together with the water. And so essentially the water brings the chemical species to different places. So this diffusive transport in this term you have the u, which is we call Darcy velocity. And then the concentration actually I probably should have explained here. The C i will be the concentration of one chemical species of a representative species i. And the C i everywhere is the same. So this is a diffusive transport. But also in a lot of systems you have reactions, right? So the last term, 4, is for the total reaction rate. And again, overall it has same units as the first term. But essentially this could be a summation of several different, let's call this equal to summation of i, which is for the chemical species i. But this i could involve in, let's say, i k different number of reactions. So essentially you'll be adding all the reactions as this chemical species i is participating in. And this i k would be the total number of reactions for i. Okay, so this is one representative equation. We write this equation form for the species i. But if you have, let's say, I put the i from 1 to n here, meaning you can have any arbitrary number we call a primary species. So if you have, let's say, 10 different chemical species, then the primary species you have n equal to 10. And you'll be writing 10 of these equations. And these equations are essentially solved. If we solve these equations you get the concentration of different chemical species as a function of time and space. So essentially the outcome of this is the temporal and spatial distribution of chemical species. So essentially you can trace them after each chemical species and you'll get how they change as a function of time and space and how in different paths they have different rates and all that. i from 1 to n. Okay, so that's what you guys will be exposed to using this code. You will be solving these equations for particular specific questions, problem applications, and then you're usually given a set of initial conditions where the concentration of different species at time zero at different locations. And then over time how these concentration of different species evolve over time. And you will see you'll learn a lot about using this code and we'll be talking more about this in each of these terms. What are they over time in different lessons we follow.