R2.3 How far? The extent of chemical change

Question 1

when is a state of dynamic equilibrium reached

Answer 1

• closed system (no exchange with surroundings),
• concentrations of reactants and products remain constant
• rate of the forward reaction is equal to the rate of the backward reaction

Question 2

what does the equilibrium law describe

Answer 2

how the equilibrium constant (K) can be determined from the stoichiometry of a reaction

Question 3

what is K a constant for, why

Answer 3

• a given temperature
• if temperature changes, K changes
• because it has a kinetic component

Question 4

what does the magnitude of the equilibrium constant indicate

Answer 4

the extent of a reaction at equilibrium

Question 5

K>1

Answer 5

concentration of products is greater than concentration of reactants

Question 6

K<1

Answer 6

concentration of reactants is greater than concentration of products

Question 7

K=1

Answer 7

equilibrium lies in the middle, favouring neither products nor reactants

Question 8

what happens to K is a reaction is endothermic and temperature is increased

Answer 8

increases

Question 9

what happens to K is a reaction is endothermic and temperature is decreased

Answer 9

decreases

Question 10

what happens to K is a reaction is exothermic and temperature is increased

Answer 10

decreases

Question 11

what happens to K is a reaction is exothermic and temperature is decreased

Answer 11

increases

Question 12

equilibrium lies to the left if

Answer 12

larger proportion of product than reactants

Question 13

equilibrium lies to the right if

Answer 13

larger proportion of reactants than products

Question 14

Le Chatelier’s principle

Answer 14

• if a system is at equilibrium, any change applied to the system tends to shift the equilibrium to counteract the effect of the applied change
• enables the prediction of the qualitative effects of changes in concentration, temperature and pressure to a system at equilibrium

Question 15

increase pressure

Answer 15

Shift to favour the direction with fewer molecules

Question 16

decrease pressure

Answer 16

Shift to favour the direction with more molecules

Question 17

increase concentration

Answer 17

Shift to the other side

Question 18

decrease concentration

Answer 18

Shift to the other side

Question 19

increase temperature

Answer 19

Shift to favour endothermic direction

Question 20

decrease temperature

Answer 20

Shift to favour exothermic direction

Question 21

addition of a catalyst

Answer 21

• no effect on the position of equilibrium
• allows the establishment of equilibrium to be reached faster

Question 22

chemical equilibrium

Answer 22

involves a chemical reaction in a closed system

Question 23

physical equilibrium

Answer 23

• involves a physical process at equilibrium within a closed system
• some physical processes involve a change of phase

Question 24

phase

Answer 24

• a homogeneous part of a heterogenous system that is separated from other parts by a distinguishable boundary
• has uniform composition

Question 25

single phase system

Answer 25

homogeneous

Question 26

system with 2 or more phases

Answer 26

heterogeneous

Question 27

homogeneous equilibria

Answer 27

reactants and products in the same phase

Question 28

heterogeneous equilibria

Answer 28

reactants and products are in different phases

Question 29

what is the reaction quotient (Q)

Answer 29

• a numerical measure of the position of equilibrium

Question 30

Q>K

Answer 30

• concentration of products is greater than at equilibrium
• favour the reverse reaction until equilibrium is reached

Question 31

Q<K

Answer 31

• concentration of reactants is greater than at equilibrium
• favour the forward reaction until equilibrium is reached

Question 32

Q=K

Answer 32

• system is at equilibrium
• forward and reverse reactions occur at the same rates

Question 33

what can be used to measure the position of an equilibrium reaction

Answer 33

• equilibrium constant
• Gibbs energy change ΔG