unit 10 gibbs

Enthalpy

Determines overall energy change (delta H) in a reaction, considering the amount of energy needed to break the bonds of reactants versus the energy involved in forming the products. The delta heat effusion for element is one a 0 kJ/mol

Entropy

The measure of disorder

Solid

Low entropy

Liquid

Medium entropy

Gas

High entropy

Pure substance

Low entropy

Mixture

High entropy

Gibbs’s free energy

A way of relating enthalpy and entropy. It is related to the capacity of a system to do work, which can be used to predict spontaneity.

If delta G is positive

Not spontaneous=no reaction

If delta G is negative

Spontaneous=reaction

If delta G is zero

Equilibrium

At high temperatures which is favored?

Entropy

If H is negative and exothermic and S is positive (disordered)

Always spontaneous

If H is negative and exothermic and S is negative (ordered)

Spontaneous at lower temperatures

If H is positive and endothermic and S is positive (disordered)

Spontaneous at higher temperatures

If H is positive and endothermic and S is negative (ordered)

Never spontaneous

Exothermic

Negative, net energy charge of a system decreases, feels hot because we take the energy. Energy exists

Endothermic

Positive, net energy charge of a system increases, feels cold because it is taking our energy, energy enters

Heat of Reaction

Amount of total heat given off measured as energy/mass

Hess’s law

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