1.6 Chemical Equilibria, Le Chatelier's Principle and Kc Flashcards

1
Q

Reactants get used up = forward reaction ___ ___

A

slows down

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2
Q

Products is formed = reverse reaction ___ __

A

speeds up

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3
Q

Define dynamic equilibrium

A

When the rate of forward reaction equals the rate of backwards reaction in a closed system

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4
Q

At dynamic equilibrium, concentrations of reactants and products ___ ____

A

stay constant

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5
Q

What is Le Chatelier’s Principle?

A

In closed system, position of equilibrium moves to oppose any change

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6
Q

Le Chatelier’s Principle only applies to reactions where …

A

every species in same physical state

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7
Q

What happens if you increase the concentration of a reactant in a reaction at equilibrium?

A
  1. Equilibrium tries to remove increase in reactant
  2. ∴ makes more product
  3. Equilibrium shifts to right
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8
Q

What happens if you increase the concentration of a product in a reaction at equilibrium?

A
  1. Equilibrium tries to remove increase in product
  2. Makes reverse reaction go faster
  3. Equilibrium shifts to left
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9
Q

Decreasing concentration has the _____ effect

A

opposite

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10
Q

What happens if you increase the pressure of a reaction at equilibrium?

A
  1. Shifts equilibrium to side with fewer moles of gas
  2. To reduce pressure/oppose the change
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11
Q

What happens if you decrease the pressure of a reaction at equilibrium?

A
  1. Equilibrium shifts to side with more moles of gas
  2. Raises pressure/opposes the change
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12
Q

What happens if you increase the temperature of a reaction at equilibrium?

A
  1. ↑ temp = adding heat
  2. Equilibrium shifts in endothermic (positive ΔH) direction to ↓ temp./oppose the change
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13
Q

What happens if you decrease the temperature of a reaction at equilibrium?

A
  1. ↓ temp = removing heat
  2. Equilibrium shifts in exothermic (negative ΔH) direction to produce more heat, to ↑ temp/oppose the change
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14
Q

Why do you get a higher yield at lower temperatures?

A
  • ∵ it’s exothermic reaction, lower temps = forward reaction
  • ∴ at lower temps = more ethene and steam is converted to ethanol
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15
Q

Why is the reaction carried out at temperatue of 300°C?

A
  • It’s a compromise between reasonable yield and faster reaction
    • Lower temps = slower rate of reaction
    • No point in getting very high yield of ethanol if it takes you 10 years
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16
Q

Why is 60-70 atm used?

A

It’s a compromise - gives reasonable yield for lowest possible cost

17
Q

Why is high pressure used?

A
  1. High pressure shifts equilibrium to side with fewer molecules = forward reaction, increases yield
  2. High pressure increases rate of reaction too
18
Q

Why is not very high pressure used? Name 2 reasons why

A
  • Very expensive ∵
    1. Power or energy required to provide high pressure
    2. Strong pressure vessel needed (to withstand high pressure)
19
Q

State the expression that Kc can be written as for the equation:
aA + bB ⇌ dD + eE

A
20
Q

Kc

Equal numbers of products and reactants = __ ____

A

no units

21
Q
A
22
Q
A
23
Q
A
24
Q

Value of Kc is only valid for one particular ____

A

temperature

25
Q

Why is the value of Kc only valid for one particular temperature?

A

Change temp of system = change equilibrium concentrations of product and reactants ∴ Kc changes

26
Q

If the temp change means there’s more product at equilibrium, what happens to Kc?

A

Kc

27
Q

If the temp change means there’s less product at equilibrium, what happens to Kc?

A

Kc

28
Q

Name 2 factors that doesn’t affect Kc

A
  • Changing conc. of reactant & product
  • Catalysts
29
Q

In industrial processes, why are not extremely high temperatures used? (2)

A
  1. High temperature is expensive
  2. Cost of plant able to resist high temperature is too high
30
Q

State the units for this expression

A

mol–2 dm+6

31
Q

Explain the effect of a catalyst on equilibrium (2)

A
  • Equilibrium unaffected/unchanged
  • Increases rate of forward and backwards reactions equally