It is the study of heat changes. Increased temperature increases molecular motion. Energy is the ability to do work. Joules (J) and calories (cal) are the most common energy units. Energy can be transferred through work applying a force over a distance.
Energy changes of physical and chemical processes
First law of thermodynamics states that energy can not be created or destroyed in physical or chemical changes. Heat is the flow of energy from higher temperature particles to lower temperature particles.
Enthalpy, entropy and free energy
Enthalpy (H) takes into account the internal energy of the sample along with pressure and volume. Under constant pressure, heat and enthalpy are the same. Enthalpy of reaction is the net energy change during a chemical reaction. In endothermic reaction, the system takes in energy from the surroundings. ΔD is positive. In exothermic reaction, the system gives off energy to the surroundings. Here, ΔH is negative. Heat capacity is the amount of energy that can be absorbed by a particle, before the temperature increases. When changing between solids, liquids and gases, the temperature does not change. Entropy is the randomness. Spontaneity occurs without outside intervention. Second law of thermodynamics states that every spontaneous process has an increase in entropy of the universe.
Determining spontaneity of a process
Spontaneity occurs without outside intervention. Temperature can determine whether a process is spontaneous. Free energy (G) relates temperature, enthalpy and entropy. Free energy is used to determine if the reaction is spontaneous at a specific temperature.
Relating free energy and equilibrium
A chemical reaction that can proceed in both directions is called a reversible reaction. A reaction is said to be at equilibrium when the rate of the forward reaction equals the rate of the reverse reaction. It takes time to establish equilibrium. The reactions continue to proceed in both directions, but at the same rate is said to be in dynamic equilibrium. At thermal equilibrium, two objects at different temperatures, placed together will come to the same temperature.