Equillibirum Module 5

Question 1

What is dynamic equilibrium?

Answer 1

The rate of the forward reaction is the same as the backwards reaction
There’s no overall change in concentrations of the reactants and products
Can only occur in a closed system at a constant temperature

Question 2

Example of dynaimic equilibrium in a physical system?

Answer 2

Br2(l) ⇋ Br2(g)

Question 3

Example of dynaimic equilibrium in a chemical system>

Answer 3

H2(g) + I2(g) ⇋ 2HI(g)

Question 4

Formula for Kc?

Answer 4

If aA +bB ⇋ cC + dD

Then Kc = ((C^c)(D^d)) / ((A^a)(B^b))
Capitals are the concentrations of chemicals in mol^1 dm^3
Lower case are the amount of moles

Question 5

How do you work out units for Kc?

Answer 5

Using indice rules cancel out the mol^1 dm^-3 on the top and bottom of equation

Question 6

What’s a homogenous reaction?

Answer 6

All the products and reactants are in the same state

Question 7

What’s the rule for finding Kc if reaction is homogeous?

Answer 7

Put all reactants and products into formula

Question 8

What’s a heterogenous reaction?

Answer 8

If the reactants and products are in different states

Question 9

What’s the rule for finding Kc if reaction is heterogenous?

Answer 9

Only aqueous and gaseous reactants and products go into formula (water needs to go in it if the solvent isn’t aqueous)

Question 10

How can you find out concentrations of unknown reactants and products if you are told Kc?

Answer 10

Rearrange the Kc formula to find the unknowns

Question 11

How to use a table to work out equillibrium concentrations?

Answer 11

Draw your table with at top the chemical equation with column for each chemical
At side have initial concentration, conc change, and equillibrium concentration
Fill in table with everything you know, the products initial concentration will always be 0
Whatever the decrease is for the products to equillibrium concentration from initial, will be the increase for the products
Remember to take moles into account

Question 12

How do you find the total pressure of a gas mixture?

Answer 12

It’s the sum of all the partial presures

Question 13

How do you find the partial pressure of a gas?

Answer 13

First find mole fraction of the gas in the mixture using Number of moles of gas / total number of all moles of gas in mixture

The multiply the mole fraction of gas by the total pressure of the mixture

So if they have the same amount of moles in equation will have the same partial pressure

Question 14

What’s the equation for Kp?

Answer 14

if aA(g) + bB(g) ⇋ cC(g) + dD(g)

Then Kp = p(C^c) x p(D^d) / p(A^a) x p(B^b)

Use the partial pressures instead of concentrations

Question 15

How do you work out units for Kp?

Answer 15

Cancel out kPa on top and bottom

Question 16

How can you work out unknown partial pressures if told Kp?

Answer 16

Rearrange equation to find it

Question 17

What’s le Chatelier’s principle?

Answer 17

If there’s a change in concentration, pressure or temperature the equillibrium will move to counteract the change

Question 18

What does a higher value of Kp or Kc mean?

Answer 18

Equilibrium lies further to the right

Question 19

If the forward reaction is endothermic and you increase temperature what happens

Answer 19

Equilibrium shifts to the right, Kc or Kp affected

Question 20

If the forward reaction is exothermic, what does an increase in temperature do?

Answer 20

Equilibrium shits to the left, Kc or Kp affected

Question 21

Does concentration or pressure changes affect Kp or Kc?

Answer 21

No

Question 22

Rules of what concentration changes does to position of Equilibrium?

Answer 22

If you increase the concentration of the chemical the Equilibrium will shift to the other side

If you decrease the concentration of a chemical the Equilibrium will shift to the side of the chemical

Question 23

What does increasing the pressure do to the position of Equilibrium?

Answer 23

Shifts to the side of equilibrium with fewer gas molecules

Question 24

What do catalysts do to the position of Equilibrium?

Answer 24

They have no affect, and also don’t affect Kp or Kc

However they do Equilibrium is approached faster