Chemistry Chapter 4: Equilibrium and Thermodynamics Flashcards
Connecting energy and reaction quotient
ΔG = ΔG° + RT ln Q, where Q describes the reaction quotient ([product]/[reactants]) at a given moment.
Difference between Q and K
Q= [reactants]/[products]
This represents the ratio of product to reactant concentrations at any given moment during the reaction.
Q can change depending on the current concentrations of reactants and products.
K= [reactants]/[products] at equilibrium.
𝐾 a fixed value for a given reaction at a specific temperature and represents the ratio of products to reactants when the reaction is at equilibrium.
If Q > K
The reaction will shift toward the reactants to reach equilibrium.
If K < Q
The reaction will shift toward the reactants to reach equilibrium.
K = Q
The reaction is at equilibrium; no net change occurs.
Gibbs free energy and equilibrium if a) not at equilbrium and b) at equilibrium
b) ΔG = 0 at equilbrium and Q = Keq
Difference between ΔG′° and ΔG°
ΔG° = Standard Free Energy Change
ΔG′° = Biochemical Standard Free Energy Change
Adjusts for biological conditions, specifically:
pH = 7 (instead of 1 M H⁺ like in standard conditions)
Water is at 55 M (but typically omitted from equilibrium expressions)
Sometimes accounts for specific ionic conditions relevant to biological systems
What is a standard enthalpy of formation reaction look like
enthalpy change when 1 mole of the compound is formed from its elements in their standard states.
Hess’s law
Are equilibrium constants temperature dependant?
YES because changes in temperature affect the relative rates of the forward and reverse reactions, shifting the equilibrium position according to Le Chatelier’s Principle.
What to do if the MCAT asks about entropy of a reaction
When the MCAT asks you about entropy, simply look to phase changes and count up the number of moles of gas present in both the reactants and the products. More moles of gas means more entropy.
In this example there is no change in entropy
