Unit 10 - Equilibrium

When is chemical equilibrium reached?

• when the rate of both forward and reverse reactions are equal

• when the concentration of reactants and products are constant (NOT EQUAL!)

What type of reaction can reach equilibrium?

reversible reactions

What does it mean when the rate of the forward reaction is greater than the reverse reaction?

more products are being made; the reaction is proceeding to the right

What does it mean when the rate of the reverse reaction is greater than the forward reaction?

more reactants are being made; the reaction is proceeding to the left

Are there any observable changes when a reaction reaches equilibrium?

no because the forward and reverse reactions are happening at the same time and rates

How is chemical equilibrium maintained?

• system must be closed (nothing can enter or leave)

• volume must remain the same (constant partial pressure)

• temperature must remain the same to maintain the same rxn rates

What is the equilibrium constant (K_eq)?

the [ ] of products raised to their stoichiometric coefficients divided by the [ ] of reactants raised to their stoichiometric coefficients

Is K_eq the same at all temperatures during a reaction?

no, K_eq is temperature dependent

What phases of matter should be included in a K_eq expression?

only gases and aqueous substances

(NO liquids or solids)

What does K_eq tell us about a reaction?

it tells us whether the reactants or products are favored when equilibrium is reached

What does a K_eq > 1 mean?

products are favored at equilibrium

What does K_eq < 1 mean?

reactants are favored at equilibrium

What is the reaction quotient (Q)?

tells you the general concentration of products and reactant at any moment in time; same expression as K_eq

What does it mean when Q < K_eq?

the reaction with proceed to the right to make more products to reach equilibrium

What does it mean when Q > K_eq?

the system will proceed to the left to make more reactants to reach equilibrium

What does it mean when Q = K_eq?

the system is at equilibrium

What is a different form of the K_eq expression that can be used when dealing with gases only?

you can use partial pressure values instead of concentration

(use round parentheses not brackets)

What is the coefficient rule?

when the coefficients in a reaction equation are multiplied by a factor of n, the K_eq value is raised to the n power

What is the reciprocal rule?

if a reaction is reversed, its K_eq is the inverse/reciprocal of the initial K_eq value

What is the multiple equilibria rule?

when two or more reactions are combined, the K_eq is the product of the individual K_eq values of each reaction