Equilibira

Question 1

What is the formula for equilibrium constant?

Answer 1

Kc = [products]^ratio / [reactants]^ratio

Question 2

What does it mean if Kc value is 1?

Answer 2

The concentration of products and reactants is the same

Question 3

What does it mean if Kc value is >1?

Answer 3

The equilibrium position lies towards the products

Question 4

What does it mean if Kc value is <1?

Answer 4

The equilibrium position lids towards the restarts

Question 5

What does a dynamic equilibrium exist?

Answer 5

A dynamic equilibrium exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of reactants and products does not change

Question 6

What is Le Chatelier’s Principle?

Answer 6

Brings back to equilibrium (effect of temperature pressure or concentration on the position of equilibrium)

Question 7

What is homogenous equilibrium?

Answer 7

Contains equilibrium species that all have the same state or phase

Question 8

What is heterogenous equilibrium?

Answer 8

Contains equilibrium species that have different states or phases (Kc only includes in Thai case species that are (g) or (aq))

Question 9

What is mole fraction?

Answer 9

• Under the same conditions of temperature and pressure, the same volume of different gases contains the same number of moles of gas molecules
• The mole fraction of a gas is the same as it’s proportion by volume to the to volume of gases in a gas mixture

Question 10

What is the mole fraction x(A)?

Answer 10

Number of moles of A / total number of moles in gas mixture

Question 11

What is the partial pressure of a gas?

Answer 11

• In a gas mixture the partial pressure, p of a gas is the contribution that the gas makes towards the total pressure P
• The sum of the partial pressures of each gas equals the total pressure

Question 12

What is the partial pressure for gas A?

Answer 12

p(A) = mole fraction of A x total pressure P

Question 13

What does a catalyst do to the equilibrium?

Answer 13

A catalyst increases the rate of both forward and reverse reactions in an equilibrium by the same amount resulting in an unchanged position of equilibrium

Question 14

What happens if the temperature changes?

Answer 14

K changes and the ratio of products and reactants change to reflect the new value of K

Question 15

What happens when you increase the temperature of an exothermic forwards reaction and why?

Answer 15

1. Decrease K
2. Increased temperature, decreased K as reactant concentration must increase to reflect the lower K so the equilibrium shifts to the left

Question 16

What happens when you decrease the temperature of an exothermic forwards reaction and why?

Answer 16

1. Increase K
2. Decreased temperature, increase in K as the concentration of the products must increase to reflect the higher K so the equilibrium shifts to the right

Question 17

What happens when you increase the temperature of an endothermic forwards reaction and why?

Answer 17

1. Increased K
2. Increased temperature, increased K and so concentration of products must increase to reflect the higher k and so equilibrium shifts to the right

Question 18

What happens when you decrease the temperature of an endothermic forwards reaction and why?

Answer 18

1. Decreased K
2. Decreased temperature, decreased K and so concentration of reactants must increase to reflect lower K so the equibliruum shifts to the left

Question 19

What happens to K if you change the concentration?

Answer 19

If the concentration changes, K does not change so the ratio of pro cuts and reactants changes to rerun to the value of K

Question 20

What happens when you increase the concentration of one of products?

Answer 20

1. No effect of Kc
2. Concentration of products decreased to return to the original value
3. So equilibrium shifts to the left

Question 21

What happens when you increase the concentration of one of reactants?

Answer 21

1. No effect of Kc
2. Increasing [reactant] disrupts equilibrium
3. Concentration of products increased to return to original Kc value
4. So equilibrium shifts to the right

Question 22

What happens to Kc and pressure?

Answer 22

If the pressure changes, k does NOT CHANGE so the ratio of products and reactants change to return to the value of K

• Kc does not change
• System is now no longer in equilibrium (increased pressure increases concentration terms on bottom of Kc expression more than the top)
• Top of Kc expression increases and bottom decreased until Kc is reached

Question 23

What happens as you increase the pressure?

Answer 23

1. No effect on Kp
2. Increasing pressure disrupts equilibrium
3. Increase in pressure of (less moles side) to return to original Kp value do equilibrium shifts to the right

Question 24

What happens when you decrease the pressure?

Answer 24

1. No change to Kp
2. Decreasing pressure disrupts equilibrium
3. Increase the partial pressure of A and B (more moles side) to return to original Kp value
4. Equilibrium shifts to the left

Question 25

If pressure increases how does Kp change? (specific example)

Answer 25

1. Equilibrium position shifts to the right/ forwards/towards products
2. Ratio in Kp expression decreases or bottom of Kp expression increases more than the top
3. Ratio in Kp expression increases to restore Kp or numerator/top of Kp expression increases to restore Kp

Question 26

When are results concordant?

Answer 26

0.1 difference