PMT 1.6 - Chemical Equilibria, Le Chatelier's principle and Kc Flashcards

Define the term dynamic equilibrium.

Define the term dynamic equilibrium.

The rate of the forward reaction is equal to the rate of the reverse reaction.

(Hence, the concentrations of reactant and product do not change)

Give an essential condition for an equilibrium mixture.

Give an essential condition for an equilibrium mixture.

●Equilibrium occurs in a closed system (where reactants and products cannot escape)

OR

●Macroscopic properties do not change with time

State Le Chatelier's principle.

State Le Chatelier's principle.

If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance.

In the equation:

CH4(g) + H2O(g)⇌CO(g) + 3H2(g)

ΔH°= +210 kJ mol-1

What effect would increasing the temperaturehave on the position of equilibrium?

In the equation:

CH4(g) + H2O(g)⇌CO(g) + 3H2(g)

ΔH°= +210 kJ mol-1

What effect would increasing the temperaturehave on the position of equilibrium?

The equilibrium position shifts to the right.

(This is because the forward reaction is endothermic. Yield of hydrogen increases.)

In the equation:

CH4(g) + H2O(g)⇌CO(g) + 3H2(g)

ΔH°= +210 kJ mol-1

What effect would increasing the pressurehave on the position of equilibrium?

In the equation:

CH4(g) + H2O(g)⇌CO(g) + 3H2(g)

ΔH°= +210 kJ mol-1

What effect would increasing the pressurehave on the position of equilibrium?

The equilibrium position shifts to the left.

This is because the forward reaction is produces more moles of gas than the reverse reaction (4 moles of product, 2 moles of reactant). Yield of hydrogen decreases.

The reaction:

CH4(g) + H2O(g)⇌CO(g) + 3H2(g) ΔH°= +210 kJ mol-1

Suggest and explain why an industrial chemist may use a high pressure for this production of hydrogen from the above reaction?

The reaction:

CH4(g) + H2O(g)⇌CO(g) + 3H2(g) ΔH°= +210 kJ mol-1

Suggest and explain why an industrial chemist may use a high pressure for this production of hydrogen from the above reaction?

1.The high pressure increases the collision frequency, increasing the rate of reaction.

2.This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen.

What effect does a catalyst have on the position of equilibrium?

What effect does a catalyst have on the position of equilibrium?

No effect.

(because catalyst affects rate of forward and reverse reactions equally)

What condition affects the value of Kc ?

❑Concentration

❑Catalyst

❑Pressure

❑Temperature

What condition affects the value of Kc ?

❑Concentration

❑Catalyst

❑Pressure

❑Temperature

Temperature

For the reaction below, deduce an expression for Kc .

2[A] + 3[B] + [C] ⇌[D]+ 4[E]

For the reaction below, deduce an expression for Kc .

2[A] + 3[B] + [C] ⇌[D]+ 4[E]

Kc =[D][E]4

[A]2[B]3[C]

Deduce units for the value of Kc

Kc =[D][E]4

[A]2[B]3[C]

Deduce units for the value of Kc

Kc =[D][E]4

[A]2[B]3[C]

mol-1 dm-3

What type of system is Kcrelevant for?

What type of system is Kcrelevant for?

Homogeneous systems in equilibrium

What does Kc being greater of lesser than 1 suggest for the position of equilibrium?

What does Kc being greater of lesser than 1 suggest for the position of equilibrium?

Greater than 1 = over to the rightLesser than 1 = over to the left

What effect does decreasing the temperature in an endothermic reaction have on Kc ?

What effect does decreasing the temperature in an endothermic reaction have on Kc ?

Kc decreases

What effect does increasing the temperature in an endothermic reaction have on Kc ?

What effect does increasing the temperature in an endothermic reaction have on Kc ?

Kc increases

What effect does decreasing the temperature in an exothermic reaction have on Kc ?

What effect does decreasing the temperature in an exothermic reaction have on Kc ?

Kc increases

What effect does increasing the temperature in an exothermic reaction have on Kc ?

What effect does increasing the temperature in an exothermic reaction have on Kc ?

Kc decreases