Chapter 19 - Equilibrium

Question 1

What is homogeneous equilibrium?

Answer 1

Equilibrium species all have the same state or phase e.g. are all gases

Question 2

What is heterogeneous equilibrium?

Answer 2

equilibrium species have different states or phases

e.g. C(s) + H2O(g) CO2(g) +H2(g)

Question 3

How do you calculate Kc of heterogeneous equilibrium?

Answer 3

Substitute concentration values into Kc equation for only species that are gases or aqueous

Question 4

How do you work out amounts at equilibrium?

Answer 4

ICE table

I - initial

C - change

E - equilibrium

Question 5

Calculate Kc when 1.6 mol NO(g) and 1.4 mol O2(g) are mixed together in a container with a volume 4.0dm^3. At equilibrium, 1.2 mol NO2(g) has formed

2NO(g) + O2(g) 2NO2(g)

Answer 5

2NO + O2 2NO2

I 1.6 1.4 0

C -1.2 -0.6 1.2

E 0.4 0.8 1.2

[NO(g)] = 0.4/4 = 0.1 moldm^-3

[O2(g)] = 0.8/4 = 0.2 moldm^-3

[NO2(g)] = 1.2/4 = 0.3 moldm^-3

Kc = [NO2]² / [NO]² [O2]

= 0.3² / 0.1² x 0.2

= 45 dm³ mol^-1

Question 6

What is the mole fraction of a gas?

Give the equation for gas A

Answer 6

Same as its proportion by volume to the total volume of gases in a mixture

mole fraction x(A) = number of moles in A / total number of moles in gas mixture

Question 7

What is the partial pressure of a gas?

Give the equation for gas A

Answer 7

Contribition that gas makes towards the total pressure P. Sum of partial pressures = total pressure

For gas A: partial pressure p(A) = mole fraction of A x total pressure P

= x(A) x P

Question 8

Write the expression for Kp for H2(g) + I2(g) 2HI(g)

Answer 8

Kp = p(HI)²/ p(H2) x p(I2)

P(x) - partial pressure

Question 9

What are the 3 rules for how equilibrium shists in response to change (le chatelier)/

Answer 9

1. ) If concentration of species increases, equilibrium shifts in the direction that reduces the concentration
2. ) If the pressure is increased, the equilibrium position shifts towards the side with fewer gaseous molecules
3. ) If the temperature increases, equilibrium position shifts in the endothermic

Question 10

What does the magnitude of an equilibrium constant K indicate?

Answer 10

Extent of equilibrium

Question 11

What would k=1, k=100 and k=0.01 represent?

Answer 11

k=1 - equilibrium halfway between reactants and products

k=100 - equilibriu, in favour of products

k=0.01 - equilibrium in favour of reactants

Question 12

What is the effect of increasing temperature on k, when the forward reaction is exothermic?

Answer 12

• equilibrium constant, k, decreases with increasing temp.
• decreases equilibrium yield of products

Question 13

What is the effect on k when the temperature is increased and the forward reaction is endothermic?

Answer 13

• equilibrium constant increases
• equilibrium shifts to product side increasing yield

Question 14

What effect does increasing pressure have on a reaction with fewer moles of gaseous products than reactants

Answer 14

• Products increase
• reactants decrease
• equilibrium shifts to right

Question 15

What effect does increasing pressure have on a reaction with more moles of gaseous products than reactants?

Answer 15

• Products decrease
• Reactants increase
• equilibrium shifts to the left

Question 16

What is the effect of a catalyst on equilibrium constant?

Answer 16

• k unaffected by the presence of a catalyst. Effects the rate of reaction - speeding up forward + reverse reactions

Question 17

What effects Kc (and Kp)?

Answer 17

Change in temperature

(Isn’t affected by pressure/concentration)