1.12 Kp

Question 11

What is partial pressure?

Answer 11

In a mixture of gases, each gas exerts its own pressure = partial pressure

Question 12

What is the total pressure of a gas mixture? (i.e how you calculate it)

Answer 12

sum of all partial pressure of the individual gases

Question 13

Answer 13

Question 15

What is a mole fraction?

Answer 15

Proportion of a gas mixture that is made up a particular gas

Question 16

State how you calculate mole fraction of a gas in a mixture

Answer 16

Question 17

State how you calculate partial pressure of a gas

Answer 17

Question 19

PCl_5(g) ⇌ PCl_3(g) + Cl_2(g)

Answer 19

Question 20

What is the equilibrium constant for reversible reactions where all reactants and products are gases?

Answer 20

K_p

Question 21

State the expression for K_p

Answer 21

(Put partial pressures in expressions)

Question 22

PCl_5(g) ⇌ PCl_3(g) + Cl_2(g)

Answer 22

Question 23

Just like K_c, value of K_p is affected by _____

Answer 23

Temperature

(K_p is only valid for a given temp.)

Question 24

Explain why K_p is only valid for a given temperature

Answer 24

• ∵ changing temp. changes how much product is formed at equilibrium
• Changes mole fractions of gases present which changes their partial pressures

Question 25

Just as changing conc. doesn’t change K_c, changing _____ doesn’t affect K_p

Answer 25

pressure

Equilibrium will shift to keep it the same

Question 26

Adding a catalyst ______ K_p

Answer 26

won’t affect

Question 27

Explain what will happen to K_p if temperature is increased

Answer 27

Question 28

The rate equation for a reaction is rate = k[E]. Explain qualitatively why doubling the temperature has a much greater effect on the rate of the reaction than doubling the concentration of E. (3)

Answer 28

• Reaction occurs when molecules have E ≥ E_a
• Doubling T causes many more molecules to have this E
• Whereas doubling [E] only doubles the number with this E

Question 29

Suggest why initial rates of reaction are used to determine orders rather than rates of reaction at other times during the experiments (1)

Answer 29

At time 0, the conc. are known

Question 30

State how the initial rate is obtained from a graph of the concentration of the product against time (1)

Answer 30

• Calculate gradient of the tangent
• At t = 0 OR at start of graph

Question 31

How can you work out the rate of reaction from reactions where there’s a sudden colour change when a product reaches a certain concentration

Answer 31

• By measuring the time it takes for the colour change to happen
• Shorter the time = faster rate