Chemical Equilibria

Question 1

how can you tell when equilibrium is reached?

Answer 1

macroscopic properties do not change (e.g. density, colour, concentration and pressure)

Question 2

equilibrium is a dynamic process
what is meant by a dynamic process?

Answer 2

equilibrium is reached when forward and backwards reactions occur at the same rate yet the reaction happens continuously

Question 3

equilibrium must be in a closed system
what is meant by a closed system?

Answer 3

nothing can enter/leave

Question 4

why can equilibrium be approached from either direction?

Answer 4

eqm position will be the same if conditions are kept the same

Question 5

what is le chatelier’s principle?

Answer 5

• if a system at eqm is disturbed, the eqm moves in the direction that tends to reduce the disturbance
• only applies to homogeneous equilibria (all species in same phase)

Question 6

what are the 4 conditions that apply to all equilibria?

Answer 6

1) eqm can only be reached in a closed system
2) eqm can be approached from either direction
3) eqm is a dynamic process
4) eqm reached when macroscopic properties don’t change

Question 7

when will the proportions of an eqm mixture change?

Answer 7

• when conditions change
• at any given conditions the proportions are the same

Question 8

which way will an eqm shift if the proportion of products increases?

Answer 8

right/forward direction

Question 9

which way will an eqm shift if the proportion of reactants increases?

Answer 9

left/reverse/backward

Question 10

which direction will an eqm shift if concentration of reactants is increased? what will be the effect of this?

Answer 10

• eqm moves right
• more product made

Question 11

which direction will an eqm shift if concentration of products is increased? what will be the effect of this?

Answer 11

• eqm moves left
• more reactant made

Question 12

which direction will an eqm shift if concentration of reactants is decreased? what will be the effect of this?

Answer 12

• eqm moves left
• less product made

Question 13

which direction will an eqm shift if concentration of products is decreased? what will be the effect of this?

Answer 13

• eqm moves right
• less reactant made

Question 14

which direction will an eqm shift if pressure is decreased?

Answer 14

eqm moves to side with more gas molecules (which raises the pressure again)

Question 15

which direction will an eqm shift if pressure is increased?

Answer 15

eqm shifts to side with fewer gas molecules

Question 16

which direction will an eqm shift if temperature is increased?

Answer 16

eqm shift to endothermic side

Question 17

which direction will an eqm shift if temperature is decreased?

Answer 17

eqm shifts to exothermic side

Question 18

what effect does a catalyst have on the position of eqm?

Answer 18

• no effect
• only allows eqm to be reached more quickly

Question 19

what is the equation for the equilibrium constant (Kc)?

Answer 19

Kc = ([C][D])/([A][B])
Kc = (concentration of products)/(concentration of reactants)

Question 20

what conditions can change the Kc?

Answer 20

only temperature

Question 21

what effect will increasing Kc have on the position on eqm?

Answer 21

• eqm moves to right
• more product formed

Question 22

what effect will decreasing Kc have on the position on eqm?

Answer 22

• eqm moves to left
• more reactant formed (less product)