Equilibrium (Topics 10 & 11)

Question 1

What is equilibrium?

Answer 1

When a reaction has a constant concentration of reactants and products

Question 2

What is dynamic equilibrium?

Answer 2

there is a constant concentration of reactants and products

and the forwards and backwards reactions are taking place in both directions and at equal rates

Question 3

increasing concentration of reactants means shift to the

increasing concentration of products means shift to the

Answer 3

right (to form more product)

left (to form more reactants)

Question 4

increasing pressure causes shift to

decreasing pressure causes shift to

Answer 4

the side with fewer moles of gas (WTR - opposite of increase = fewer)

the side with more moles of gas

Question 5

What is Kc

Answer 5

concentration constant

Question 6

Write the Kc expression for

aA + bB —> cC + dD

Answer 6

[C]^c [D]^d
Kc = ——————
[A]^a [B]^b

Question 7

Kc word equation

Answer 7

concentrations of products/concentrations of reactants

Question 8

How do scientists use Kc?

Answer 8

calculate Kc, change conditions, calculate new Kc and if the value has gone up then it means equilibrium has shifted right and favoured the products.
If it has gone down, equilibrium has shifted left and favoured the reactants.

Question 9

What do you omit from the Kc equation?

Answer 9

SOLID

Question 10

Effect of catalyst on equilibrium

Answer 10

no effect on position of equilibrium but will affect rate at which equilibrium is achieved

Question 11

Why does a catalyst not effect the position of equilibrium?

Answer 11

because it speeds up the rates of the forwards and backwards reactions at the same time

Question 12

The larger the Kc…

Answer 12

the greater the amount of products

Question 13

Define partial pressure

Answer 13

pressure the gas would have had if it only occupied the volume being occupied by the mixture that the gas is in.

Question 14

partial pressure chemrevise equation

Answer 14

mole fraction of gas 1 x total pressure of gas 1

Question 15

mole fraction equation

Answer 15

no. moles of a gas/ no. moles of all the gases

Question 16

What is the only state included in Kp calculations?

Answer 16

GAS

Question 17

Write the Kp expression for

aA + bB —> cC + dD

Answer 17

P C^c x P D^d
Kp = ——————
P A^a x P B^b

Question 18

Kp units

Answer 18

atm

Question 19

Kc units

Answer 19

mol dm^-3

Question 20

Values used to predict extent a Kc/Kp reaction may occur

Answer 20

• reaction doesn’t go when; K< 10^-10
• reactants predominate in an equilibrium when: K is approximately 0.1
• equal amount of products and reactants when: Kc = 1
• products predominate in an equilibrium when: K is approximately 10
• Reaction goes to completion when: K > 10^10

Question 21

How to set out the Kc/Kp equation

Answer 21

Initial
Change
Equilibrium
[ ]
Kc/Kp
units