unit 8 - equilibrium

Question 1

chemical equilibrium is achieved when…

Answer 1

• the rates of the forward and reverse reactions are equal
• the concentrations of the reactants and the products remain constant

Question 2

formula for equilibrium constant (Kc)

Answer 2

concentration of products raised to their coefficients / concentration of reactants raised to their coefficients

LIQUIDS AND SOLIDS DO NOT COUNT

Question 3

what happens to the equilibrium constant if the reaction is…

• multiplied by n
• divided by 2
• 2 reactions are added
• reaction reversed

Answer 3

• multiplied by n: raise new equilibrium to the power of n
• divided by 2: square root new equilibrium
• 2 reactions are added: new equilibrium is the product of the 2 reactions
• reaction reversed: new equilibrium is the reciprocal of the original one

Question 4

what does the equilibrium constant tell us?

Answer 4

concentration where both products and reactants are at equilibrium

Question 5

how is the equilibrium constant affected by temperature or pressure or concentration of reactants?

also explain equilibrium constant being greater than or less than 1

Answer 5

• equilibrium constant is only dependent on temperature, nothing else matters
• less than 1: reaction favors the formation of the reactants. most of original reactant remains as reactant, little product is formed.
• greater than 1: reaction favors the formation of the products. more reactants are formed than reactants remain.

Question 6

relationship b/w Kp and Kc formula

Answer 6

Kp = K(RT)^delta n

Question 7

homogenous vs. heterogenous equilibria

Answer 7

homogenous equilibria: all in the same phase

heterogeneous equilibria: different phases

Question 8

Le Chatelier’s Principle

Answer 8

if a change is imposed on a system at equilibrium, the position of the equilibrium will shift in a direction that tends to reduce that change.

Question 9

Le Chatelier’s Principle: concentration, temperature, and pressure

Answer 9

• concentration: the system will shift AWAY from the added component. if removed, opposite effect occurs.

temperature: system shifts in direction that consumes the excess heat (favors the endothermic reaction)

pressure: shifts away from the added gaseous component. decreasing volume means increasing pressure. shifts equilibrium towards side with fewer moles of gas.

Question 10

Le Chatelier’s Principle: addition of inert (noble) gas

Answer 10

• at constant volume: it will not react and will not change concentration. so, it will not affect equilibrium.
• at constant pressure: it will increase the volume and less particles per unit volume. so, equilibrium will shift to side with more moles.

Question 11

reaction quotient (Q) and K

Answer 11

Q = K; system is at equilibrium. no shift will occur.

Q > K; system shifts to left (too many products at that point)

Q < K; system shifts to right (too many reactants)