Thermochemistry

Work

The result of a force acting through a distance.

Energy

The capacity to do work.

Heat

The flow of energy caused by a temperature difference.

Kinetic Energy

Energy associated with the motion of an object.

Thermal Energy

Energy associated with the temperature of an object; a type of kinetic energy.

Potential Energy

Energy associated with the position or composition of an object.

Chemical Energy

Energy associated with the relative positions of electrons and nuclei in atoms and molecules; a form of potential energy.

Law of Conservation of Energy

States that energy cannot be created or destroyed, only transferred between objects and transformed into different forms.

Internal Energy (e)

The sum of the kinetic and potential energies of all the particles that compose the system.

State Function

A property whose value depends only on the state of the system, not on how the system arrived at that state.

Delta E

The change in internal energy; calculated as E(final) - E(initial).

Endothermic Reaction

A reaction that absorbs heat from its surroundings, resulting in a positive delta H.

Exothermic Reaction

A reaction that gives off heat to its surroundings, resulting in a negative delta H.

Calorimetry

The measurement of the thermal energy exchanged between a reaction and its surroundings by observing the change in temperature.

Gibbs Free Energy

A criterion for spontaneity calculated as change in enthalpy minus temperature times change in entropy.

Entropy (S)

A measure of the dispersal of energy in a system.

Third Law of Thermodynamics

States that the entropy of a perfect crystal at absolute zero (0 K) is zero.

Relative Standard Entropies

Entropy of a gas is greater than that of a liquid, which is greater than that of a solid.

Allotropes

Elements that can exist in two or more forms in the same state of matter.

Standard Entropy Change

The change in entropy for a process in which all reactants and products are in their standard states.