Chapter 19 - Equilibrium

Question 1

How to calculate the units for Kc

Answer 1

1. Substitute the units into the expression for Kc.

2. Cancel any common units

Question 2

What’s a homogeneous Equilibria

Answer 2

All the species in the reaction have the same state or phase.
The Kc expression contains the concentrations of all species.

Question 3

What’s a heterogeneous Equilibria

Answer 3

Equilibrium species all have different states or phases.

The concentrations of solids and liquids are generally constant, so they are emitted from the Kc expression.

Question 4

What states are included in the Kc expression?

Answer 4

Only gaseous and aqueous.

Question 5

What’s the ICE table for calculating the Equilibrium concentration?

Answer 5

I- initial- number of moles given
C- change- reactants have a -x. This is multiplied by the number of moles in the reaction. The products are +x also multiplied.
E- equilibrium change - take away the initial moles from the change. (or add)
Then divide this by the volume given if there is a volume given.

Question 6

PAG: Determining Kc from experimental results

Answer 6

This reaction is for a carboxylic acid and alcohol.
1. In a conical flash, mix 0.1mol of the carboxylic acid and 0.1mol of the alcohol. Add in 0.05mol of HCl to act as an acid catalyst.
2. Add 0.05mol of HCl to a second conical flask to act as a control.
3. Add a stopper to both.
4. Leave for a week
5. Carry out a titration on the eq. mxiture using a standard solution of NaOH.
6. Repeat with the acid catalyst to give you the number of moles of acid in each.
Then calculate Kc.

Question 7

Define the mole fraction of a gas

Answer 7

It is the same as its proportion by volume to the total volume of gases in a gas mixture.

Question 8

Formula for the mole fraction

Answer 8

Mole fraction of A = (number of moles of A)/ total number of moles in a gas mixture.

Question 9

What is the sum of the mole fractions

Answer 9

1

Question 10

Define the partial pressure

Answer 10

In a gas mixture, the partial pressure of a gas is the contribution that the gas makes towards the total pressure (P)

Question 11

Formula for the partial pressure

Answer 11

Partial pressure of A = Mole fraction of A x total pressure (P)

Question 12

Sum of partial pressures?

Answer 12

Total pressures

Question 13

Formula for Kp

Answer 13

p (Products) / p (Reactants)

To the power of the balancing number in the equation

Question 14

Kp only uses what species?

Answer 14

Only uses gases, all other species must be ignored.

Question 15

What does the value of K show you

Answer 15

The extent of a chemical equilibrium.

Question 16

If K = 1

Answer 16

Equilibrium sits in the middle

Question 17

If K = 100

Answer 17

The equilibrium lies in favour of the products

Question 18

If K = 1 x 10-2

Answer 18

The equilibrium lies in favour of the reactants

Question 19

What affects the K?

Answer 19

Only the temperature.

Question 20

In exothermic reactions…

Answer 20

The EC decreases with increasing temperature.
When you increase the temperature, the EC shifts to the side of the endothermic change, so the reactants, and so the equilibrium yield of the products decreases.

Question 21

In endothermic reactions…

Answer 21

The EC increases with increasing temperature. When you increase the temperature, the EC shifts to the side of the endothermic change, so the products, and so the equilibrium yield of the products increases.

Question 22

How does changing the concentration and the pressure affect the K?

Answer 22

Doesn’t affect it at all. The system changes the concentration of pressures of certain chemicals only to keep the K constant in the reaction.

Question 23

How does adding a catalyst affect K

Answer 23

Still, doesn’t affect the K.

Adding a catalyst only increases the rate of the reaction, but it doesn’t affect the position of the EC.