equilibrium

Question 1

why are solids not included when finding Kp

Answer 1

their pressure is constant

Question 2

explain why the equilibrium constant would have no units

Answer 2

the units cancel

Question 3

what measurement is used for Kp

Answer 3

partial pressure

Question 4

what measurement is used for Kc

Answer 4

concentration

Question 5

how do you calculate partial pressure

Answer 5

mole fraction x total pressure

Question 6

explain one benefit to the environment of using catalysts in industry

Answer 6

reaction can occur at lower temperature so less fuel is used

Question 7

concentration of catalyst is increased; state the effect on equilibrium position and rate of attainment of equilibrium

Answer 7

no effect on position of equilibrium; equilibrium is reached faster

Question 8

how to write expressions for equilibrium constants

Answer 8

products / reactants

Question 9

CH4 + H2O <=> CO + 3H2; pressure of equilibrium is increased; state and explain the effect on Kp

Answer 9

no effect because Kp only depends on temperature (same for all equilibrium constants)

Question 10

how to write partial pressure of chemical ‘a’

Answer 10

P(a)

Question 11

how to write mole fraction of chemical ‘a’

Answer 11

X(a)

Question 12

suggest why industrial reactions never actually reach equilibrium

Answer 12

product is removed

Question 13

what is dynamic equilibrium

Answer 13

rate of forward and backward reactions are equal; concentrations of reactants and products stay constant

Question 14

forward reaction has an enthalpy change of -745 kJ/mol; state, with a reason, the effect of lowering temperature on the position of equilibrium

Answer 14

shifts to the right; exothermic in forward direction

Question 15

2NO + 2CO <=> N2 + 2CO2; state, with a reason, the effect of increasing pressure on the position of equilibrium

Answer 15

shifts to the right; in direction of fewer molecules

Question 16

CO + 2H2 <=> CH3OH; explain why increasing pressure increases the yield of methanol; give one disadvantage of increasing pressure

Answer 16

it is on the side with less molecules; more expensive equipment needed

Question 17

explain, in terms of total ΔS(total) and ΔS(surroundings), why an exothermic equilibrium gives greater yield at lower temperature

Answer 17

ΔS(surroundings) becomes more positive (because reaction is exothermic for -ΔH/T); so ΔS(total) becomes more positive

Question 18

how to increase an equilibrium’s atom economy without changing temp or pressure

Answer 18

remove product as it is formed; recycle unreacted reactants