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A-level Chemistry: 3.1.6 Chemical Equilibria

Chemistry28 CardsCreated 2 months ago

This deck covers key concepts of chemical equilibria, including dynamic equilibrium, Le Chatelier's Principle, and the effects of concentration, pressure, and temperature changes on equilibrium. It also explores the equilibrium constant (Kc) and its dependencies.

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Reactants get used up = forward reaction ___ ___

slows down
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Key Terms

Term
Definition
Reactants get used up = forward reaction ___ ___
slows down
Products is formed = reverse reaction ___ __
speeds up
Define dynamic equilibrium
When the rate of forward reaction equals the rate of backwards reaction in a closed system
At dynamic equilibrium, concentrations of reactants and products ___ ____
stay constant
What is Le Chatelier’s Principle?
In closed system, position of equilibrium moves to oppose any change
Le Chatelier’s Principle only applies to reactions where …
every species in same physical state
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A-level Chemistry: 3.1.6 Chemical Equilibria
TermDefinition
Reactants get used up = forward reaction ___ ___
slows down
Products is formed = reverse reaction ___ __
speeds up
Define dynamic equilibrium
When the rate of forward reaction equals the rate of backwards reaction in a closed system
At dynamic equilibrium, concentrations of reactants and products ___ ____
stay constant
What is Le Chatelier’s Principle?
In closed system, position of equilibrium moves to oppose any change
Le Chatelier’s Principle only applies to reactions where …
every species in same physical state

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

  1. Equilibrium tries to remove increase in reactant

  2. ∴ makes more product

  3. Equilibrium shifts to right

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

  1. Equilibrium tries to remove increase in product

  2. Makes reverse reaction go faster

  3. Equilibrium shifts to left

Decreasing concentration has the _____ effect
opposite

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

  1. Shifts equilibrium to side with fewer moles of gas

  2. To reduce pressure/oppose the change

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

  1. Equilibrium shifts to side with more moles of gas

  2. Raises pressure/opposes the change

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

  1. ↑ temp = adding heat

  2. Equilibrium shifts in endothermic (positive ΔH) direction to ↓ temp./oppose the change

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

  1. ↓ temp = removing heat

  2. Equilibrium shifts in exothermic (negative ΔH) direction to produce more heat, to ↑ temp/oppose the change

Why do you get a higher yield at lower temperatures?

  • ∵ it’s exothermic reaction, lower temps = forward reaction

  • ∴ at lower temps = more ethene and steam is converted to ethanol

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

  • 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

Why is 60-70 atm used?
It’s a compromise - gives reasonable yield for lowest possible cost

Why is high pressure used?

  1. High pressure shifts equilibrium to side with fewer molecules = forward reaction, increases yield

  2. High pressure increases rate of reaction too

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

  • Very expensive ∵

    1. Power or energy required to provide high pressure

    2. Strong pressure vessel needed (to withstand high pressure)

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

Equal numbers of products and reactants = __ ____
no units
Value of Kc is only valid for one particular ____
temperature
Why is the value of Kc only valid for one particular temperature?
Change temp of system = change equilibrium concentrations of product and reactants ∴ Kc changes
If the temp change means there's more product at equilibrium, what happens to Kc?
Kc ↑
If the temp change means there's less product at equilibrium, what happens to Kc?
Kc ↓
Name 2 factors that doesn't affect Kc
Changing conc. of reactant & product Catalysts

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

  1. High temperature is expensive

  2. Cost of plant able to resist high temperature is too high

mol–2 dm+6

Explain the effect of a catalyst on equilibrium (2)
Equilibrium unaffected/unchanged Increases rate of forward and backwards reactions equally