take the microscopic point of view. They are presented elsewhere in this website (click the underlined subject above to see more). Thermochemistry - It is the application of the first law of thermodynamics (conservation of energy) to processes such as: chemical reactions, phase changes, e.g., boiling and melting, and the formation of solutions. The first thermochemistry law (proposed in 1780) states that: the quantity of heat required to decompose a compound into its elements is equal to the heat evolved when that compound is formed from its elements. The second law of thermochemistry (discovered experimentally in 1840, also known as Hess law). It states that the heat change in a chemical reaction is the same whether it takes place in one or several stages. That is, the heat change depends on the initial and final states only (Figure 12-19). Chemical Kinetics - Chemical kinetics study reaction rates in a chemical reaction. It is measured by the amount of reactant used up, or the amount of product formed, in a certain period of time. Reactions with low activation energies go faster than reactions with high activation energies. The rate of a reaction can be affected by the temperature, the amounts of reactants in the container, and catalysts (Figure 12-20). Reactions almost always go faster at higher temperatures, because the increase in kinetic energy makes the reactants move faster and collide more often. The rate of a reaction also increases when reactants are added (resulting in higher concentration) since there are more