equillibrium 2

Question 1

Dynamic equilibrium occurs when…

Answer 1

• forward and backward reactions are occurring at equal rates
• The concentrations of reactants and products stays constant

Question 2

aA + bB —> cC + dD

Kc =

Answer 2

[ C]c [D]d / [ A]a [B]b

Question 3

square brackets [ ] means…

Answer 3

the equilibrium concentration

Question 4

moles of reactant at equilibrium =

Answer 4

initial moles – moles reacted

Question 5

moles of product at equilibrium =

Answer 5

initial moles + moles formed

Question 6

practical to work out Kc?

Answer 6

A common experiment is working out the equilibrium constant for an esterification reaction.
- Ethanol and ethanoic acid are mixed together with a sulfuric acid catalyst.

Question 7

how to work out initial amount of moles of reactants

Answer 7

mass = density x volume
then
moles= mass / Mr

Question 8

The initial amount of moles of acid catalyst used is usually determined by…

Answer 8

titrating a separate sample of catalyst with sodium hydroxide

Question 9

If a reaction contains gases an alternative equilibrium expression can be set up using the…

Answer 9

partial pressures of the gases instead of concentrations

Question 10

the partial pressure of a gas in a mixture is…

Answer 10

the pressure that the gas would have if it alone occupied the volume occupied by the whole mixture

Question 11

If a mixture of gases contains 3 different gases then the total pressure will equal…

Answer 11

the 3 partial pressure added together

Question 12

partial pressure =

Answer 12

mole fraction of gas 1 x total pressure of gas 1

Question 13

mole fraction=

Answer 13

number of moles of a gas / total number of moles of all gases

Question 14

Kp expressions only contain…

Answer 14

gaseous substances.
- Any substance with another state is left out

Question 15

The larger the Kp, the greater the amount of…

Answer 15

products

Question 16

If K, is small we say the equilibrium favours the…

Answer 16

reactants

Question 17

Kc and Kp only change with…

Answer 17

temperature
- They do not change if pressure or concentration are altered.
- A catalyst also has no effect on K, or K

Question 18

Both the position of equilibrium and the value of Kc or Kp will change if…

Answer 18

temperature is altered

Question 19

effect of temperature on the position of equilibrium

Answer 19

• If temperature is increased the reaction will shift to oppose the change and move in the endothermic direction.
• If temperature is decreased the reaction will shift to oppose the change and move in the exothermic direction.

Question 20

Effect of temperature on rate

Answer 20

As the temperature increases a significantly bigger proportion of particles have energy greater than the activation energy, so the frequency of successful collisions increases.
RATE INCREASES

Question 21

Effect of concentration on position of equilibrium

Answer 21

Increasing concentration of 1 reactant, would move equilibrium to the right lowering concentration of all reactants and increasing concentration of products. The new concentrations would restore the equilibrium to the same value of Kc

Question 22

Effect of concentration and pressure on rate

Answer 22

At higher concentrations(and pressures) there are more particles per unit volume and so the particles collide with a greater frequency and there will be a higher frequency of effective collisions.

Question 23

Effect of pressure on position of equilibrium

Answer 23

If pressure is increased the reaction will shift to oppose the change and move in the direction to the side with fewer moles of gas.
If pressure is decreased the reaction will shift to oppose the change and move in the direction to the side with more moles of gas.

Question 24

Effect of catalysts on position of equilibrium and Kc

Answer 24

A catalyst has no effect on the position of equilibrium or values of Kc and Kp but it will speed up the rate at which the equilibrium is achieved.

Question 25

why doesn’t a catalyst effect the position of equilibrium?

Answer 25

because it speeds up the rates of the forward and backward reactions by the same amount

Question 26

Catalysts speeds up the rate allowing…

Answer 26

lower temperatures to be used (and hence lower energy costs) but have no effect on equilibrium.

Question 27

yield and rate at low temperatures?

Answer 27

Low temp gives good yield but slow rate

Question 28

yield and rate at high pressures?

Answer 28

High pressure gives good yield and high rate

Question 29

high pressure leads to…

Answer 29

too high energy costs for pumps to produce the pressure and too high equipment costs to have equipment that can withstand high pressures.

Question 30

how can we improve the overall yields of all these processes and improve atom economy?

Answer 30

by recycling unreacted reactants back into the reactor