3.2.3: Chemical equilibrium Flashcards

1
Q

What does dynamic equilibrium mean?

A

It occurs when the rate of forward reaction equals the rate of reverse reaction and the concentration of reactants and products remain constant in a closed system

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2
Q

Changing what factors can alter the position of equilibrium?

A

● Concentration of reactants or products
● Pressure
● temperature

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3
Q

Explain the Le Chatelier’s principle

A

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

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4
Q

What effect would increasing the temperature have on the position of equilibrium?
In the equation: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)
ΔH°= +210 kJ mol-1

A

The equilibrium position shifts to the right.
(This is because the forward reaction is
endothermic. Yield of hydrogen increases.)

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5
Q

What effect would increasing the pressure have on the position of equilibrium?
In the equation: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)
ΔH°= +210 kJ mol-1

A

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). Therefore the yield of hydrogen decreases.

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6
Q

Suggest and explain why an industrial chemist may use a high pressure for the production of hydrogen from: CH4(g) + H2O(g) ⇌ CO(g) + 3H2(g)
ΔH°= +210 kJ mol-1

A

The high pressure increases the collision frequency
thus increasing the rate of reaction.
This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen

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7
Q

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

A

No effect.
(because catalyst affects rate of forward
and reverse reactions equally)

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8
Q
What condition affects the value of Kc?
❑ Concentration
❑ Catalyst
❑ Pressure
❑ Temperature
A

temperature

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9
Q

For the reaction below, deduce an expression for Kc .

2[A] + 3[B] + [C] ⇌ [D]+ 4[E]

A

Kc = [D][E] ^4/[A]^2[B]^3[C]

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10
Q

Deduce units for the value of Kc

A

mol-1 dm-3

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11
Q

What type of system is Kc relevant for?

A

Homogeneous systems in equilibrium

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12
Q

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

A

Greater than 1 = over to the right

Less than 1 = over to the left

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13
Q

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

A

Kc decreases

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14
Q

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

A

Kc increases

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15
Q

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

A

Kc increases

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16
Q

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

A

Kc decreases