Unit 5 Chem Notes

Exothermic Reaction

Any reaction that releases energy in the form of heat, light, sound, electricity, or motion.

Endothermic Reaction

A reaction that absorbs energy in the form of heat.

Enthalpy (ΔH)

Energy changes that occur during a reaction, represented by the energy released or absorbed as heat by a system at constant pressure.

Thermochemical Equation

An equation that includes the quantity of energy as heat released or absorbed during the reaction as written.

Hess’s Law

The overall enthalpy change in a reaction is equal to the sum of the enthalpy changes for the individual steps in the process.

ΔH

The energy change enthalpy, where negative indicates an exothermic reaction and positive indicates an endothermic reaction.

Constant-Pressure Calorimeter

Measures enthalpy changes at constant pressure, suitable for reactions in solution.

Bomb Calorimeter

Measures enthalpy changes at constant volume, typically for reactions that produce large amounts of gas.

Enthalpy of Reaction

Heat absorbed or released during a chemical reaction at constant pressure, an extensive property.

Bond Energy

The energy required to break a bond in a molecule; breaking bonds absorbs energy while forming bonds releases energy.

Spontaneous Processes

A system that can change without a decrease in enthalpy will do so with an increase in entropy.

Standard Temperature and Pressure (STP)

Conditions often used for measuring enthalpy, defined as 25 °C (298 K) and 1 atm.