The Effect of Changes in Conditions on Equilibrium Position

Question 1

how is a change in the position of equilibrium done

Answer 1

• by changing a condition of the reaction

- like temperature or the concentration of substances

Question 2

if you add an acid to a yellow solution containing chromate ions and the product is dichromate ions (which make the solution orange) and water, what effect would adding more acid have on the equilibrium and why

Answer 2

• it would change the position of equilibrium to the right
• as a higher concentration of hydrogen ions leads to more frequent reactions between them and the chromate ions
• so more dichromate ions would be produced

Question 3

what colour change would be observed if more acid was added to the solution and why

Answer 3

• it would go from orange to a darker shade of orange

- because the concentration of dichromate ions has increased

Question 4

what would happen if you added more alkali to the solution

Answer 4

• the equilibrium would shift to the left
• as more chromate ions would be produced from the reaction between the OH- ions and the dichromate ions
• so the conc of chromate ions would increase while for dichromate it decreases

Question 5

what are the 4 main factors that affect the position of equilibrium

Answer 5

• concentration of a component
• pressure of the system
• temperature of the system
• addition of a catalyst

Question 6

what would happen to the equilibrium position if the concentration of one of the reactants was increased

Answer 6

it would shift to the right

Question 7

why would it shift to the right

Answer 7

• because the rate of the forward reaction would increase so more product is formed
• as the conc of the products increases the rate of the backward reaction also increases until a new equilibrium is established

Question 8

where would the equilibrium shift if:

1. conc of reactants increased
2. conc of reactants decreased
3. conc of products increased
4. conc of products decreased

Answer 8

• 1 = to the right
• 2 = to the left
• 3 = to the left
• 4 = to the right

Question 9

what kind of reactions would changes in pressure have any impact in

Answer 9

reversible reactions involving gases

Question 10

what are the two factors you can control in a practical if you want to change the pressure

Answer 10

• the volume containing the gas

- the number of moles of gas used

Question 11

what would increasing or decreasing the volume do to the pressure

Answer 11

• increasing the volume would decrease pressure

- decreasing the volume would increase pressure

Question 12

what would increasing or decreasing the number of moles of reactants do to the pressure

Answer 12

• increasing the moles would increase the pressure

- decreasing the moles would decrease the pressure

Question 13

if the pressure was increased in all cases, where would the change in position of equilibrium go if the ratio between the number of moles of reactants and products were:

1. more to fewer
2. fewer to more
3. same to same

Answer 13

• 1 = to the right
• 2 = to the left
• 3 = no change

Question 14

if the temperature of a reversible reaction was increased, how would the rates of the forward and backward reaction change first and foremost

Answer 14

• they would both increase

- for the reasons why an increase in temp causes a reaction to occur quicker

Question 15

where and what would the difference in the rate of reaction be instead

Answer 15

• the rate of the endothermic reaction would be increased more than the rate of the exothermic reaction would be increased

Question 16

what would an increase in temperature therefore shift the equilibrium

Answer 16

in the direction of the endothermic reaction (so usually to the left)

Question 17

if the reaction was exothermic, where would the equilibrium shift if the temperature:

1. increased
2. decreased

Answer 17

• 1 = to the left

- 2 = to the right

Question 18

if the reaction was endothermic, where would the equilibrium shift if the temperature:

1. increased
2. decreased

Answer 18

• 1 = to the right

- 2 = to the left

Question 19

what would be the effects on the rates of reaction of adding a catalyst to a reversible reaction

Answer 19

the rate of the forward and backward reaction would increase

Question 20

how would the position of equilibrium change due to the catalyst

Answer 20

• the increase in the rate of reaction will be the same for both directions
• so the equilibrium position would not be changed

Question 21

what is an advantage to adding a catalyst at the beginning of a reaction

Answer 21

it will reduce the time required to establish equilibrium

Question 22

what is a bid disadvantage that comes with making these qualitative predictions

Answer 22

• they are just predictions
• some reactions might have multiple factors playing a role at once
• which makes predicting the direction of change impossible at times

Question 23

in the reaction 2NO2(g) = N2O4(g) which is placed in hot water, why would complications arise when trying to determine the position the equilibrium shifts to

Answer 23

• there are too many equilibrium-affecting factors at play to know which one or which combination is more significant
• the temperature, pressure and moles of gases all have their own effects

Question 24

in this case how does temperature change the equilibrium position

Answer 24

• there is an increase in temperature
• so the equilibrium would shift to the endothermic direction
• so it would shift to the left

Question 25

how would the change in pressure change the equilibrium position

Answer 25

• as the gases are being heated up in the water the pressure is increasing
• meaning the equilibrium would shift to the side with less moles (the right)