Thermodynamics is the general study of energy, the different forms it may assume, and the transitions between the forms. Energy is broadly defined as the ability to do work or supply heat. Since energy in any of its forms is still energy, it is always measured in units of Joules (or equivalent units). Thus mechanical energy, chemical energy, and thermal energy are measured in Joules. Another common unit of energy is the calorie, equivalent to 4.184J. The unit usually used to measure the heat content of food is the Kcal, which is equal to 1000 calories. An additional conversion is 101 J=1 liter*atmosphere. Energy may be stored as kinetic energy in the motion of the particles or as potential energy due to the position of the particles. In the case of kinetic energy, an increase in temperature increases the speed of the particles and thus the kinetic energy of the substance. Particles tend to minimize their potential energy. Thus, hydrogen gas exists as and not as 2H because has a lower potential energy.
Applying the principles of thermodynamics to chemistry yields predictions about the amount of heat released by different reactions. This area is the study of thermochemistry. State properties of substances in chemical reactions depend only on the state of the substance. For example, state properties of water at 25¬°C are independent of whether the water was formed by the hydrolysis of oxygen and
