A2-Level Rates of Reaction

  • A rate equation can be used to show how the rate of a reaction changes considering all the reactants’ concentrations.

  • A rate constant, k, is used in the rate equation to account for the influence of temperature on the rate of a reaction. A rate constant is only for a given temperature.

  • Different reactions can have different rate constant values and the units can also be different.

  • In the rate equation, each concentration of reactant is raised to the power of its order and multiplied by the rate constant, k.





     

QUICK NOTES

The Rate Equation

 

If we know all of the orders with respect to reactants in a reaction, we can link them all together to see how the rate of a reaction changes when we consider all the concentrations of reactants. This is called the rate equation.

 

It is not just the concentrations of reactants that influences the rate of a reaction. The rate of reaction also changes with temperature and a small change in temperature can lead to a big change in a rate of reaction.  A rate constant, k, is used to link the effect of concentrations at a particular temperature together.

 

Key point: a rate constant, k, is only for a given temperature. If you change the temperature, the value of k also changes and every reaction has a different value for k. The units of k are not fixed, and k can have different units for different reactions.

 

 

 

If we wanted to construct a rate equation for the above example, we have to combine the individual orders for all the reactants and multiply them by the rate constant, k.

 












 

Each concentration of reactant is raised to the power of its order.

 

 

 

Anything raised to the power zero = 1, therefore [A] = 1. This means we can now simply put in the rate equation instead of [A]

 

 

 

 

 

Anything raised to the power 1 just equals itself, [B] = [B].

 

 

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