Topic 1.6 - Chemical Equilibria, Le Chatelier’s principle and K c

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16 Terms

1
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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)

2
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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

3
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State Le Chatelier’s

principle.

If a system at equilibrium is disturbed,

the equilibrium moves in the direction

that tends to reduce the disturbance.

4
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CH 4(g) + H 2 O (g) ⇌ CO (g) + 3H 2(g)

ΔH°= +210 kJ mol-1

What effect would increasing the temperature

have on the position of equilibrium?

The equilibrium position shifts to

the right.

(This is because the forward reaction is endothermic.

Yield of hydrogen increases.)

5
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In the equation:

CH 4(g) + H 2 O (g) ⇌ CO (g) + 3H 2(g)

ΔH°= +210 kJ mol-1

What effect would increasing the pressure

have 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.

6
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The reaction:

CH4(g) + H 2 O (g) ⇌ CO (g) + 3H 2(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.

7
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What effect does a catalyst

have on the position of

equilibrium?

No effect.

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

8
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What condition affects the value of K c ?

Temperature

9
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2[A] + 3[B] + [C] ⇌ [D]+ 4[E]

knowt flashcard image
10
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Deduce units for the value of K c

knowt flashcard image
11
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What type of system is K c

relevant for?

Homogeneous systems in

equilibrium

12
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What does K c being greater

of lesser than 1 suggest for

the position of equilibrium?

Greater than 1 = over to the right

Lesser than 1 = over to the left

13
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What effect does decreasing the

temperature in an endothermic

reaction have on K c ?

K c decreases

14
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What effect does increasing the

temperature in an endothermic

reaction have on Kc ?

K c increases

15
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What effect does decreasing the

temperature in an exothermic

reaction have on K c ?

K c increases

16
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What effect does increasing the

temperature in an exothermic

reaction have on K c ?

K c decreases