Enthalpy

Energy Definition

Energy is the capacity to do work (w) or to produce heat (q)

law of conservation of energy

energy can be converted from one form to another, but can be neither created nor destroyed.

Temperature

property that measures the average kinetic energy of particles in a substance

Heat definition

transfer of thermal energy between two substances due to a temperature difference

Thermodynamics

The study of energy and its interconversions

first law of thermodynamics

the energy of the universe is constant

Enthalpy

heat absorbed or released in a chemical reaction at constant pressure

Endothermic Reaction

 

• H_products > H_reactants

• Heat is gained by system

• ΔH is (+)

Exothermic Reaction

• H_products < H_reactants

• Heat is lost by system

• ΔH is (−)

standard enthalpy of formation (ΔH_f°)

the change in enthalpy that accompanies the formation of 1 mole of that substance from its elements in their natural (standard) states

Hess’s Law

if a chemical equation can be expressed as the sum of a series of steps, then the enthalpy of reaction for the overall equation is the sum of the enthalpies for each step

• If a chemical equation is reversed, the sign of ΔH is reversed.

• If a coefficient in a balanced chemical equation is multiplied by a factor, then the value of ΔH is multiplied by the same factor.