Now when looking at chemical changes, in order to determine the change in entropy, we're going to look at it very simplistically. We're going to say entropy change of chemical reactions are determined by the number of moles of products. So here we take a look in the first image, we're talking about increasing our entropy. So that means the change in entropy is going up.
If we look at our example, we have one mole of reactant and then if we look at the number of products, we have two moles of reactant of product. The number of moles of product has gone up, so there's an increase in moles of product. More product being made means there's more chaos, more disorder, therefore a higher change in entropy.
How about decreasing entropy? Well, here decreasing entropy will mean we're going down in terms of changing entropy. Here we have initially 1 mole of nitrogen gas, 3 moles of hydrogen gas or 4 total moles. When we transition over to the product side, we only have two moles of product, so we have less moles at the end, which means there's less chaos, less disorder and therefore less entropy.
So if there's a decrease in the moles of product, usually that means that there's going to be a decrease in the change in entropy. So just look at it simplistically as that is my number of moles going up when I transition to products or is it going down? This will determine the overall change in our entropy. So look at this in this simplistic type of way.