thermochemistry

Thermochemistry

The study of heat energy absorbed or released in chemical reactions or phase changes.

System

The part being studied in thermodynamics (e.g., a hand warmer).

Surroundings

Everything else outside the system in thermodynamics.

Potential Energy

Energy of position, stored in chemical bonds, determined by type and number of bonds.

Kinetic Energy

Energy of motion formed when chemical bonds break.

Law of Conservation of Energy

Energy is never created or destroyed, only changes form.

Heat

Energy that flows from warmer to cooler objects.

Temperature

A measure of hotness or coldness, not total energy.

Calorie

Heat needed to raise 1 g of water by 1°C.

Specific Heat Capacity

Amount of heat needed to raise 1 g of a substance by 1°C.

Calorimetry

The measurement of heat absorbed or released in a chemical reaction.

Specific Heat Equation

Equation used to calculate heat: q = m c ΔT.

Enthalpy

Heat content of a system at constant pressure.

Exothermic Reaction

A reaction that releases energy, with ΔH negative.

Endothermic Reaction

A reaction that absorbs energy, with ΔH positive.

Hess's Law

If multiple reactions add up to a final reaction, their ΔH values also add.

Reaction Rate

Change in concentration over time, measured in M/s or mol/L/s.

Collision Theory

A theory stating that a reaction occurs only if particles collide with sufficient energy and correct orientation.

Activation Energy (Ea)

Minimum energy needed to form the activated complex for a reaction.

Le Chatelier’s Principle

A system will shift to relieve stress when changes are made.

Chemical Equilibrium

State in which forward and reverse reaction rates become equal, and concentrations stay constant.

Phase Change Enthalpy

Enthalpy change associated with phase transitions, such as melting and boiling.