2.4 Chemical Equilibria

Question 1

What are the requirements of Equilibrium?

Answer 1

• Closed system
• A constant temperature and pressure
• Reversible reaction
• Rates of opposing changes are equal

Question 2

Properties of Equilibrium

Answer 2

• Dynamic
• Independent of starting point
• Mixed composition

Question 3

What does the reaction quotient, Q, do?

Answer 3

It relates the amounts of reactants and products to each other at any point of the reaction

Question 4

What is Qc?

Answer 4

Reaction quotient in concentration

Question 5

What is Qp?

Answer 5

Reaction quotient in partial pressure

Kpa, atm

Question 6

What is the Equilibrium Constant, K?

Answer 6

Value of the reaction quotient (Q) at Equilibrium

Question 7

What do you exclude in Equilibrium expressions?

Answer 7

Solids and Solvents

Substances which DONT have a significant change in concentration

Question 8

What is the name for everything in a Equilibrium expression being in the same pysical state

Answer 8

Homogeneous Equilibrium

Question 9

What determines whether to use Kc or Kp?

Answer 9

The units

If concentration units, eg. Mol, use Kc

If pressure units, eg. atm, use Kp

Question 10

What is a Heterogeneous equilibria?

Answer 10

Involves things in different physical states

Remember, solids and solvents are excluded

Question 11

What is excluded particularly in Kp expressions

Answer 11

Anything that doesn’t produce pressure

Eg. H2O (l)

Question 12

Status of a reaction when Q and K are the same?

Answer 12

Equilibrium

Question 13

What is the status of a reaction when Q is smaller than K?

Answer 13

Bottom of expression is larger, more reactants

Reaction will go towards the products >

Question 14

What is the status of a reaction when Q is bigger than K?

Answer 14

Top of expression is bigger, more products

Reaction will go towards the reactants <

Question 15

What does a small values of K show?

Answer 15

Equilibrium lies to the LHS

Reaction stops progressing when there are a large amount of reactants left.

Question 16

What does a large value of K show?

Answer 16

Equilibrium lies to RHS

Forward reaction continues until theres mostly products and little reactants left

Question 17

Equation relating Gibbs to the equilibrium position

Answer 17

ΔG = -RTln(Kc)

Question 18

Small K value in gibbs

Answer 18

Small K gives negative value of ln(kc)
This multipled to -RT, give positive value

Reaction is NOT spontaneous

Question 19

Large K in gibbs

Answer 19

Large K gives positive value of ln(kc)
This multipled to -RT, give negative value

Reaction IS spontaneous

Question 20

What is Le Chateliers Principle?

Answer 20

When a change is applied to a system in dynamic equilibrium, the system reacts to oppose the change

Question 21

What is an isotonic solution?

Answer 21

Osmotic equilibria

Question 22

Which equilibria does increasing pressure does not affect?

Answer 22

Those that do not involve gases

Question 23

What effect do catalysts have on equilibrium reactions?

Answer 23

Do not affect K or the position of equilibrium, just get to it faster

Question 24

Effects of temperature on exothermic reactions

Answer 24

Increasing favours REVERSE

Decreasing favours FORWARD

(think surroundings)

Question 25

Effects of temperature on Endothermic reactions

Answer 25

Increasing favours FORWARD

Decreasing favours REVERSE

(think surroundings)