equilibria (I)

Question 1

what does Le Chatelier’s principle state

Answer 1

if a change is made to a system in dynamic equilibrium the position of equilibrium moves to counteract the change

Question 2

what does it mean when a reaction is in dynamic equilibrium

Answer 2

• the rate of the forward reaction is equal to the backwards reaction
• the concentrations of the products and reactants remain constant

Question 3

describe the effect of increase in temperature on a reaction in dynamic equilibrium

Answer 3

• an increase in temperature will favour the endothermic reaction, increasing the yield of the endothermic substance

Question 4

describe the effect of decrease in temperature on a reaction in dynamic equilibrium

Answer 4

• equilibrium will shift to favour the exothermic reaction, increasing the yield of the exothermic substances

Question 5

is the forward reaction endothermic or exothermic with an enthalpy change of +65 kjmol-1

Answer 5

endothermic

Question 6

describe the effect of increase in pressure on a reaction in dynamic equilibrium

Answer 6

equilibrium will shift to the side with the fewest moles of gas (to release built up pressure)

Question 7

describe the effect of decrease in pressure on a reaction in dynamic equilibrium

Answer 7

equilibrium will shift to the side with the greatest moles of gas

Question 8

describe the effect of increase in concentration of products/reactants on a reaction in dynamic equilibrium

Answer 8

equilibrium will shift to the opposite side of the reaction
- (increasing conc of products will shift equilibrium in the direction of the backwards reaction)
- (increasing conc of reactants will shift equilibrium in the direction of the forwards reaction)

Question 9

which type of system is affected by change in pressure, temperature and concentration

Answer 9

a homogenous system

Question 10

do catalysts have an effect on the position of equilibrium and why

Answer 10

• no
• it will speed up the rate of the forwards and backwards reaction equally
  (speeding up rate in which equilibrium is reached but with no effect on yield)

Question 11

what are the conditions for making ethanol from ethene and water

Answer 11

• 60 atm pressure
• 300 degrees celsius
• phosphoric acid catalyst (H3PO4)

Question 12

what is the equilibrium constant

Answer 12

Kc

Question 13

How is Kc worked out

Answer 13

products/reactants (in square brackets to signify they are concentrations)

Question 14

what is homogeneous equilibrium

Answer 14

both reactants and products are in the same state

Question 15

what is heterogeneous equilibrium

Answer 15

some of the reactants and products are in different states

Question 16

why arent solids and pure liquids included in Kc expression

Answer 16

their concentrations remain constant throughout the reaction

Question 17

what is a high Kc value

Answer 17

where there are more products than reactants

Question 18

what is a low Kc value

Answer 18

where there are more reactants than products

Question 19

Haber process equation

Answer 19

N2(g) + 3H2(g) –> 2NH3(g)

Question 20

what is continuous flow

Answer 20

an industrial process where reactants are constantly added and products are constantly removed

Question 21

in terms of the Haber process what occurs with an increase in pressure

Answer 21

• equilibrium will shift to the right to the side with the smallest number of moles (2)
• the yield of ammonia will increase

Question 22

in terms of the Haber process what occurs with an increase in temperature

Answer 22

• the position of equilibrium will favour the endothermic reaction and shift to the left
• decreasing the yield of ammonia

Question 23

describe the conditions used in the haber process

Answer 23

• optimum conditions used for a high yield

Question 24

why is it bad that Haber process requires a decrease in temperature

Answer 24

low temperature means low rate of reaction

Question 25

why is it bad that the Haber process requires a high pressure

Answer 25

• high pressure expensive to maintain + equipment needed expensive
• H2 is very explosive under high pressures, it isnt safe

Question 26

Describe the conditions used in the Haber process

Answer 26

• optimum conditions used for a high yield
• 450 degrees celsius temperature
• 200 atm pressure
• heterogeneous iron catalyst (in solid state)

Question 27

why is a catalyst used in Haber process despite them having no effect on yield

Answer 27

due to use of continuous flow, this assures the reaction shifts forward with the catalyst

Question 28

what happens with any unreacted hydrogen or nitrogen in the Haber process

Answer 28

they get re-cycled and react again

Question 29

how is ammonia removed for continuous flow in the Haber process

Answer 29

ammonia is condensed then removed

Question 30

where is nitrogen taken from in the Haber process

Answer 30

• taken from the atmosphere (78% nitrogen in atmosphere)
• economical as large quantity of it, that humans dont need

Question 31

where is hydrogen taken from in Haber process

Answer 31

• comes from natural gas
• for example methane

Question 32

reaction of methane and water to produce hydrogen

Answer 32

CH4 + 2H2O –> CO2 + 4H2

Question 33

what is the aim of industrial and pharmaceutical processes

Answer 33

• maximise percentage yield
• make products as quickly as possible
• keep cost as low as possible
• have high atom economy (100% in Haber process as only desired NH3 formed)