AC6: Equilibria

Question 1

What are the 3 characteristics of a dynamic equilibrium

Answer 1

-The rate of the forward reaction and backward reaction is equal, so the concentration of substance in the mixture do not change
- Equilibrium can only be established if the system is closed
- If a system us at equilibrium, the temperature, pressure of concentration of each substance remain constant

Question 2

What is the general formula of Kc

Answer 2

Kc = [Product] x [Product] / [Reactant] x [Reactant]
And always remember the molar number infront of the substance in the equation you put to the power e.g 2NH3 = [NH3] ^2

Question 3

What is the only factor that will change the value of Kc

Answer 3

Temperature

Question 4

What are the units of Kc

Answer 4

Dependent on the reaction, just cancel the equation to calculate the units

Question 5

List 3 ways to follow change in concentration

Answer 5

• Change in absorption of light, if one of the substances is coloured
• Change in pH, if one of the reactants is acid or alkaline
• Titration of one of the reactants

Question 6

When you are given a question about equilibrium but not given the moles of the substances at equilibrium what must you do first before calculating Kc

Answer 6

Find moles at start of reaction
Find moles at equilibrium
Find change in the moles
Change in moles will be proportional to all the substances in the reaction
The calculating concentration to sub into the Kc equation

Question 7

If Kc is larger, what does that mean about the position of equilibrium

Answer 7

Lies over to the right

Question 8

What does Le Chatelier’s Principle states will happen to position of equilibrium when temperature increases

Answer 8

It’ll shift in the endothermic direction

Question 9

When the temperature increases, the equilibrium shifts in the endothermic direction, what does that do to the equilibrium constant

Answer 9

Changes it’s value

Question 10

If the equilibrium shifts left, what effect does that have on Kc

Answer 10

Kc gets smaller since the number on the bottom lien gets bigger

Question 11

If the equilibrium shifts right, what effect does that have on Kc

Answer 11

Kc gets bigger since the top line of the equation gets bigger

Question 12

Does pressure change the value of Kc

Answer 12

No

Question 13

When the pressure changes in an equilibrium, why does the equilibrium shift to the side with the fewer moles of gas

Answer 13

To maintain concentrations of both reactants and products that are consistent with Kc

Question 14

What is the effect of a catalyst on the position of equilibrium and the value of Kc, and why

Answer 14

There is no effect on either since a catalyst increases the rate of both the forward and backward reaction by the same factor

Question 15

When the Kc is larger than the correct Kc, so the reaction isn’t a equilibrium, what must happen to correct this

Answer 15

The top line needs to decrease and the bottom line needs to increase to decrease the value of Kc. So the equilibrium shifts left so more reactants are formed than products

Question 16

When there are multiple gases in a container, how they exert their pressures

Answer 16

Independently

Question 17

All the partial pressure in a container must add to what

Answer 17

The total pressure of the container

Question 18

What is the general formula for Kp

Answer 18

Partial pressure of products multiplied together / the partial pressure of the reactants multiplied together

Question 19

If Kp is a big number, where is the equilibrium positioned

Answer 19

To the right

Question 20

If Kp was a small number, where is the equilibrium positioned

Answer 20

To the left

Question 21

What are the units Kp

Answer 21

Depends on the equation, so cancel all of the units from the reaction , just like Kc, the unit will kPa or atm minus etc.

Question 22

How do you calculate the mole fraction of each gas in the equation, when given the moles of all the gases

Answer 22

Moles of gas A / Moles of all the gases

Question 23

What should all the mole fractions add up to

Answer 23

One

Question 24

How do you find the partial pressure of a gas after finding the mole fraction of that gas

Answer 24

mole fraction x total pressure

Question 25

What should all the partial pressures of all the gases add up to

Answer 25

The total pressure

Question 26

What is the only thing that can change the value of Kp

Answer 26

Temperature

Question 27

If the system is not at equilibrium, what won’t be consistant with Kp

Answer 27

The partial pressures

Question 28

What is meant by homogeneous equilibria

Answer 28

All the species are in the same phase / same state

Question 29

What is meant by heterogeneous equilibrium

Answer 29

One or more of the species are in different phases / states

Question 30

In heterogeneous equilibrium, what 2 states are excluded from the Kc equation

Answer 30

Liquids and solids

Question 31

Why are liquids and solids excluded from heterogeneous equilibrium

Answer 31

Because the concentrations are considered to be effectively constant