11: Equilibrium 2

Question 1

When is the Kp and Kc value applicable?

Answer 1

Only applies to a system in equilibrium

Question 2

What are the stoichiometric amounts?

Answer 2

Number of molecules in the equation

Question 3

What is the Kc equation?

Answer 3

Kc = ([C]^c[D]^d) / ([A]^a[B]^b)

Question 4

What is Kc called?

Answer 4

The equilibrium constant

Question 5

What state of elements are found in the Kc equations?

Answer 5

Solids and pure liquids are ignored as they cannot have variable concentrations

Question 6

When does Kc not change?

Answer 6

When the temperature is constant Kc is constant

This explains Le Chatelier’s principle

Question 7

What are the units of Kc?

Answer 7

Depends on the reaction involved

Each concentration is mol/dm^3

Question 8

What is it called when the Kc has no units?

Answer 8

Dimensionless

Question 9

What does it mean when Kc is large?

Answer 9

Much higher concentration of products than reactants at equilibrium

Question 10

What does it mean when Kc is small?

Answer 10

Very little amount of products and a large amount of reactants at equilibrium

Question 11

What does it mean when Kc is about 1?

Answer 11

Roughly equal amounts of products and reactants at equilibrium

Question 12

What happens to equilibrium constants when you change the concentrations of things at equilibrium?

Answer 12

Changing concentrations has no effect on Kc

Only thing that changes Kc is a change in temperature

Question 13

What happens to the position of equilibrium when concentrations are changed?

Answer 13

Le Chatelier’s principle states that concentration change means that the position of equilibrium moves to undo the change made
This is done so Kc is maintained

Question 14

What occurs to the equilibrium constants when the pressure is changed?

Answer 14

Pressure changes causes no change in the equilibrium constants

Question 15

What occurs to the position of equilibrium when the pressure is changed?

Answer 15

May be changed according to Le Chatelier’s Principle to undo the change which you have made
If pressure is increased will move to the side with less moles of gas decreasing it

Question 16

What is the equation of Kp?

Answer 16

Kp = (Pc x Pd) / (Pa x Pb)
P = partial pressure

Question 17

When should Kp be used?

Answer 17

When there is an all-gas equilibrium

Question 18

What is the equation to calculate partial pressure?

Answer 18

Partial pressure = Mole fraction of A x total pressure at equilibrium

Question 19

What occurs in the Kp equation when there are the same number of moles on each side?

Answer 19

The pressures cancel out so the equation is just the mole fractions
Therefore pressure has no effect on position of equilibrium

Question 20

If the forward reaction is endothermic and the temperature is increased, what is the effect on Kc & Kp?

Answer 20

Increase temp increases the products
Kc and Kp increases
Opposite for exothermic

Question 21

If the forward reaction is endothermic and the temperature is decreased, what is the effect on Kc & Kp?

Answer 21

Decreased temp decreases the products
Kc and Kp decreases
Opposite for exothermic

Question 22

In the reaction N2O4 -> 2NO2 the pressure is lowered, what is observed?
(NO2 is a brown gas)

Answer 22

Firstly the colour lightens as the brown gas is spread over a larger volume
Then the colour darkens as the equilibrium shifts to the right producing more brown

Question 23

What is the total pressure in a mixture?

Answer 23

Sum of all the partial pressures

Question 24

What is the equation for mole fraction?

Answer 24

Mole fraction of a gas = number of moles of gas / total number of moles of gas in the mix

Question 25

What states are included in Kp in a heterogeneous reaction?

Answer 25

Only the gases

Question 26

What happens to the equilibrium constant if the temp changes?

Answer 26

If temp change means less product forms, equilibrium constant decreases
If temp change means more product forms, equilibrium constant increases

Question 27

What does a catalyst do to equilibrium?

Answer 27

No effect on position of equilibrium

Equilibrium is reached faster

Question 28

What are the equilibrium moles in this reaction?
N2 + 3H2 -> 2NH3
Initial moles: 10, 0, 10
Equilibrium:x,y,9

Answer 28

x = 10.5
y = 1.5
As lost on the right side, there is a gain on the left side

Question 29

How can a colorimeter be used to measure equilibrium?

Answer 29

When a system is in equilibrium, the colour will remain constant

Question 30

How do you explain a dimensionless Kc?

Answer 30

Equal number of moles on either side of the reaction so the units cancel

Question 31

What does it show when two values are very similar in a titration related to equilibrium?

Answer 31

Results are within error / concordant

Shows the fact the equilibrium can be reached from either direction, rate of forward = rate of backwards reaction