19 - Equilibrium

Question 1

Homogenous equilibria

Answer 1

contains equilibrium species that all have same state/phase.

Question 2

Heterogenous equilibria

Answer 2

contains species that have different states or phases.

Question 3

what do you not include in kc expression

Answer 3

any species that are solid or liquid

Question 4

what do you include in kc expression

Answer 4

species that are (g) or (aq)

Question 5

how to find kc

Answer 5

1 - make a race table to find equilibrium moles
2 - use n=cv to find equilibrium CONCENTRATION
3 - then use Kc formula

Question 6

how to get Kc experimentally - whole method

Answer 6

Question 7

mole fraction

Answer 7

fraction of the total number of moles that each chemical in a reaction is responsible for

Question 8

write kc expression for N2 + 3H2 -> 2NH3 (reversible)

Answer 8

Question 9

Answer 9

Question 10

what is partial pressure

Answer 10

contribution that the gas makes towards the total pressure

the pressure that would be exerted by a gas in a mixture of gases if it occupied the same volume on its own at the same temperature

Question 11

sum of partial pressures

Answer 11

• Sum of partial pressures of each gas equals total pressure.

Question 12

sum of mole fractions

Answer 12

1

Question 13

how to find partial pressure

Answer 13

total pressure X mole fraction

Question 14

what is kp

Answer 14

• like Kc but partial pressure replace concentration

Question 15

units of partial pressure

Answer 15

kPa / Pa / atm

Question 16

Answer 16

Question 17

Answer 17

Question 18

how to calculate kp from heterogeneous equilibrium

Answer 18

only use gaseous species

Question 19

effect on kc / kp if you increase temp on an exothermic reaction, in forward direction

Answer 19

• if temp increases kp decreases
• kp expression / ratio of products : reactants is now greater then kp
• so we need to lower the fraction
• decrease numerator - decrease products + increase denominator - increase reactants
• shifts towards left
• equilibrium reached is now equal to new kp

Question 20

effect on kc if increase temp on an endothermic reaction, in forward direction

Answer 20

• if temp increases kp increases
• kp expression / ratio of products : reactants is now less then kp
• so we need to increase the fraction
• increase numerator - increase products + decrease denominator - decrease reactants
• shifts towards right
• equilibrium reached is now equal to new kp

Question 21

changes in conc and pressure on kc

Answer 21

• Value of equilibrium constant K is unaffected by changes in concentration/pressure.
• Equilibrium shift changes and results from the fact that equilibrium constant doesn’t change.

Question 22

what happens if increase conc of reactants (LHS)

Answer 22

• denominator of kc / kp expression larger
• kc / kp itself does not change
• ratio of products: reactants is less than kc
• to return back to normal - increase fraction
• increase numerator - increase products + decrease denominator - decrease reactants
• shifts to right

Question 23

effect of catalyst on equilibrium

Answer 23

speeds up both forward and reverse reactions in equilibrium by same factor

Equilibrium is reached quicker but position is not changed.

Question 24

how would you work out the units of kp

Answer 24

the same way you work out the units of kp

Question 25

how could the amount of iodine be determined in this reaction

2HI (g) -> H2 (g) + I2 (g)

Answer 25

A colorimeter could be calibrated using known concentrations of iodine vapour.

The concentration of iodine in the equilibrium mixture could then be determined

Question 26

where do you put the ‘p’ in the kp formula

Answer 26

inside the bracket - check mark schemes

Question 27

how would you calculate the total pressure of a system using kp

Answer 27

calculate the amount of moles of each component at equilibrium

calculate mole fractions

calculate partial pressures of each component in term os total pressure (P)

substitute into kp formulla