Heat is given off to the surroundings, and that extra heat increases the entropy of the surroundings. If you only calculate the entropy change of the reaction (the entropy change of the system), you are leaving out an important factor. If you do need to read this page, make sure you have read the page explaining how you calculate the entropy change of the system first. You will still probably have to be able to work out the feasibility of reactions, but that will be done by the rather less confusing use of an equation based on Gibbs free energy. Note: If your syllabus doesn't specifically mention entropy change terms like system, surroundings and total, you could safely ignore this page. It goes on to look at how you can use the total entropy change to decide whether or not a reaction is feasible. This page considers various entropy changes: of the system, of the surroundings, and the total change.
