Why Chemical Reactions Happen

I originally picked up this book from the library as it was on a university reading list. As an interesting analysis of the concepts behind chemical reactions, I can say that its presence there is not unwarranted. Why Chemical Reactions Happen covers ideas from entropy to atomic and molecular orbitals to kinetics and energetics. Keeler and Wothers start by introducing the book as intended for those starting a university chemistry/natural sciences course, or for those who have completed A-Levels (high-school) in chemistry as a way of furthering their understanding. I think that they succeed in presenting the relevant topics to the titular question in a straightforward manner: constructing an argument as the chapters progress.

Synopsis of concepts covered
The book begins with the idea of entropy, or disorder in physical systems. The authors show how formulating the Second Law of thermodynamics in terms of net entropy increase can reveal why both endo- and exothermic processes can occur. Water freezing is an example of an exothermic process. Above 0C, the heat given out raises the entropy of the surroundings less than below 0C. Below 0C, this entropy increase outweighs the entropy decrease by the water freezing and becoming ordered. Consequently, the process only occurs below 0C. This is analogous to chemical processes, where reactions will take place only if the net entropy decreases. An endothermic process such as the dissolution of ammonium nitrate occurs because the entropy decrease due to the heat absorbed is outweighed by the decrease in order of the solute. An expression for the Gibbs energy of a system is also derived, which has the advantage that it is derived wholly from system properties. A negative Gibbs energy indicates an increase in entropy, and consequently a possible process. The result is that reactions which reduce Gibbs energy, as opposed to enthalpy, are the ones which will occur (even though many do both.)