Calorimetry

• Calorimetry is the laboratory technique used to measure the heat released or absorbed during a chemical or physical change.

• heat capacity (Cp),which is the quantity of heat needed to change the temperature 1 K.

• the molar heat capacity (C), the amount of heat needed to change the temperature of 1 mol of a substance by 1 K.

Laws of Thermodynamics

• The First Law of Thermodynamics states that the total energy of the universe is constant.

• Entropy (S ) is related to the disorder of a system.

• The Second Law of Thermodynamics states that all processes that occur spontaneously move in the direction of an increase in entropy of the universe (system + surroundings).

Products Minus Reactants

Enthalpies

• The enthalpy change, △H, is equal to the heat gained or lost by the system under constant-pressure conditions.

• If DH > 0 the reaction is endothermic.

• If DH < 0 the reaction is exothermic.

• Hess’s law states that if a reaction occurs in a series of steps, then the enthalpy change for the overall reaction is simply the sum of the enthalpy changes of the individual steps.

• The standard enthalpy of formation of a substance (DHf°) is the change in enthalpy when 1 mol of the substance is formed from its elements when all substances are in their standard states.

Entropies

• △H ° was determined, the standard molar entropies (S °) of

elements and compounds can be tabulated. The standard molar entropy is the entropy

associated with 1 mol of a substance in its standard state.

Gibbs Free Energy

• The Gibbs free energy (G) is a thermodynamic function that combines the enthalpy,

entropy, and temperature:

• G = H - TS, where T is the Kelvin temperature