AP Chemistry 9.1-9.6 Basic Overview

Entropy

Entropy

The dispersal of matter and energy in a given sample of matter.

Entropy Increases when:

Particles are more free to move, ex. phase change from solid to liquid, or liquid to gas, along with temperature increases

Entropy increases in gases when

volume increases OR if total number of moles of gaseous products>total number of gaseous reactants, entropy increases

Delta S

A measure of the change in entropy of a system, calculated by subtracting the sum of the entropy of the reactants from the sum of the entropy of the products.

Gibbs free energy

A thermodynamic quantity that measures the energy available in a system to do useful work at a constant temperature and pressure.

∆G

The change in Gibbs free energy that occurs during a chemical reaction, which determines whether the reaction is thermodynamically favorable or unfavorable. Found with ΔG=∑G(products)−∑G(reactants) or with ΔG=ΔH-TΔS

Thermodynamically favorable

A reaction that occurs spontaneously, releasing energy, and has a negative ∆G value.

Thermodynamically unfavorable

A reaction that requires energy input and has a positive ∆G value, making it non-spontaneous.

Kinetic Control

Refers to processes that are favorable but do not make products at a measurable rate.

Catalyst

A substance (e.g. enzyme) that lowers the activation energy (Ea) required for a chemical reaction to occur, thus increasing the reaction rate, but has no effect on the favorability of the reaction.

thermodynamically favored (ΔG<0)

products are favored at equilibrium (K>1)

at equilibrium

no net change in concentration of reactants and products occurs

R

The gas constant, which relates the energy of a system to its temperature and pressure. R = 8.314 J mol-1 K-1

T

The absolute temperature of a system, measured in Kelvin.

K

The equilibrium constant of a reaction, found using the formula K=e^(-ΔG/RT).

ΔG° Equation

The standard free energy change of a reaction, found using the formula ΔG° = -RTlnK.

Negative ΔG

K>1, reaction favors products

ΔG is positive

K<1, reactions favors reactants

ΔG=0

reaction is at equilibrium

Coupling Reactions

when two reactions share an intermediate, they can be coupled, Hess’s law can be applied and the sum of the reactants’ ΔG values makes overall process favorable when added