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Rates and equilibrium for AQA A-level Chemistry

Rates and equilibrium

This page covers the following topics:

1. Calculating Kc
2. Calculating Kp
3. Rate equations
4. The rate constant

At equilibrium, the concentrations of the products and reactants will be constant but not equal. Kc is the equilibrium constant, expressing these equilibrium concentrations combined.

aA + bB โ‡Œ cC + dD

Calculating Kc

Equilibrium constants can be explained in terms of partial pressures of gases, Kp. It can be expressed from the equation for a reversible reaction.

aA + bB โ‡Œ cC + dD

Calculating Kp

Rate equations describe the rate of reaction in terms of concentration and order of the reaction with respect to each reactant. The rate constant k varies depending on the reaction.

Rate equations

The rate constant for a reaction various with temperature and activation energy. This is shown by the Arrhenius equation.

The rate constant

1

Calculate Kc when 2.43 x 10โปยณ mol lโปยน Hโ‚‚ and 2.43 x 10โปยณ mol lโปยน Brโ‚‚ react to form 3.59 mol lโปยน HBr.

Kc = 2.18 x 10โถ

Calculate Kc when 2.43 x 10โปยณ mol lโปยน Hโ‚‚ and 2.43 x 10โปยณ mol lโปยน Brโ‚‚ react to form 3.59 mol lโปยน HBr.

2

Give the expression for Kc.

image

Give the expression for Kc.

3

Calculate Kp given a an equilibrium system where partial pressures of reactant A, product B and product C are 37.5 atm, 10.3 atm and 5.60 atm respectively.

1.54 atm

Calculate Kp given a an equilibrium system where partial pressures of reactant A, product B and product C are 37.5 atm, 10.3 atm and 5.60 atm respectively.

4

Given the rate equation rate = k[B]ยฒ, what does this suggest about reactant A?

The reaction is 0 order with respect to A. The concentration of A doesn't affect the reaction rate.

Given the rate equation rate = k[B]ยฒ, what does this suggest about reactant A?

5

Calculate the rate constant of a combustion reaction at 330 K with activation energy 45 kJ molโปยน. A = 6.2 x 10ยณ molโปยน dmยณ sโปยน and R = 8.31 J Kโปยน molโปยน.

4.6 x 10โปโท molโปยน dmยณ sโปยน

Calculate the rate constant of a combustion reaction at 330 K with activation energy 45 kJ molโปยน. A = 6.2 x 10ยณ molโปยน dmยณ sโปยน and R = 8.31 J Kโปยน molโปยน.

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