19) Equilibrium

Question 1

Define homogenous equilibrium

Answer 1

an equilibrium in which all the species making up the reactants and products have the same physical state

Question 2

Define heterogeneous equilibrium

Answer 2

an equilibrium in which the species making up the reactant and products have different physical states

Question 3

Why does Kc only include species that are (g) or (aq)?

Answer 3

concentration of solids and liquids are essentially constant

Question 4

How do you calculate equilibrium quantities?

Answer 4

1. equation
2. reacting amounts
3. initial / mol
4. change / mol (using the balancing numbers of equation)
5. equilibrium / mol
6. divide by total volume to give equilibrium concentrations

Question 5

Under the same conditions of temp. and pressure, the same vol. of dif. gases contains _ moles of gas molecules?

Answer 5

the same number of

Question 6

mole fraction x (A) = ?

for gas A in a gas mixture

Answer 6

no. moles of A / total no. of moles in gas mixture

Question 7

sum of mole fractions = ?

Answer 7

1

Question 8

What is the mole fraction of a gas the same as?

Answer 8

its proportion by volume to the total vol. of dif. gases in a gas mixture

Question 9

In a gas mixture, what is the partial pressure p of a gas?

Answer 9

the contribution that the gas makes towards the total pressure P

Question 10

The sum of partial pressures = ?

Answer 10

total pressure

Question 11

partial pressure p (A) = ?

for gas A in a gas mixture

Answer 11

mole fraction of A x total pressure P

Question 12

What is the equilibrium constant for gaseous species only? What does it use?

Answer 12

Kp

p = equilibrium partial pressure in curly brackets ()

Question 13

What is the only condition that will cause k to change its value?

Answer 13

temperature change

Question 14

For an equilibrium where the forward reaction is exothermic, describe what will happen to k with an increase in temperature and its consequent effects?

Answer 14

k decreases
equilibrium shifts to the left
ratio of products / reactants > Kp (or Kc)
partial pressures (or concentration) of products decreases
partial pressures (or concentration) of reactants increases
a new equilibrium will be reached where the ratio of products / reactants is equal to the new Kp or Kc value

Question 15

For an equilibrium where the forward reaction is endothermic, describe what will happen to k with an increase in temperature and its consequent effects?

Answer 15

k increases
equilibrium shifts to the right
ratio of products / reactants < Kp (or Kc)
partial pressures (or concentration) of products increases
partial pressures (or concentration) of reactants decreases
a new equilibrium will be reached where the ratio of products / reactants is equal to the new Kp or Kc value

Question 16

Why does the position of equilibrium shift due to changes in concentration or pressure?

Answer 16

value of k unaffected

ratio of products to reactants changes to get back k

Question 17

Do catalysts affect k or the position of equilibrium?

Answer 17

no - they only affect rate

Question 18

Describe the changes that happen when concentration of products is increased

Answer 18

ratio of products to reactants > kc
no longer in equilibrium
[reactants] must increase and [products] must decrease
ratio is restored = Kc
position of equilibrium shift to left

Question 19

Describe the changes that happen when concentration of reactants is increased

Answer 19

ratio of products to reactants < kc
no longer in equilibrium
[reactants] must decrease and [products] must increase
ratio is restored = Kc
position of equilibrium shift to right

Question 20

What will a doubling in pressure result in?

Answer 20

a doubling of the partial pressures and concentration of both reactants and products

Question 21

If there are fewer molecules of gaseous products, describe the changes that happen when pressure is doubled

Answer 21

ratio of products to reactants < k
reactants must decrease and products must increase
position of equilibrium shift to right

Question 22

If there are more molecules of gaseous products, describe the changes that happen when pressure is doubled

Answer 22

ratio of products to reactants > k
reactants must increase and products must decrease
position of equilibrium shift to left

Question 23

If there are equal numbers of molecules of both gaseous reactants and products, describe the changes that happen when pressure is doubled

Answer 23

ratio = k
no change in reactants and products
no equilibrium shift