# Rates of Reaction

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## Measuring the Rate

Rate of reaction = How far a reaction proceeds in a given time

You can measure the rate by:

• Using a stopwatch to time  how long it takes to reach a certain point
• Using a gas cylinder to measure how much gas is produced in a given amount of time
• Counting bubbles given off in a given amount of time
• Measuring the weight before and after
• Measuring the precipate formed
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## Collision Theory

• Reactions take place when particles collide with a certain amount of energy
• The minimum amount of energy needed for the particles to react is called the activation energy and is different for each reaction.
• If particles dont have enough energy, they wont be able to react

The rate depends on:

• Frequency of collisions between particles
• Amount of energy with which the particles collide

You can increase the rate by:

• Increasing temperature
• Increasing the surface area
• Concentration/ Pressure
• Use of a catalyst

The rate of reaction is fastest at the beginning where there is 100% of reactant, so the frequency on collisions is very high. The rate stops when the line on a graph levels out as there are no reactants left so the frequency of collisions is 0%

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## Factors affecting Rates of Reaction

Surface area:

• Smaller objects mean a larger surface area
• A larger surface area means that more of the reactant can react at the same time, so the frequency of collisions is higher.

Temperature:

• The higher the temperature, the faster the rate as the particles have more kinetic energy so the frequency of collisions increases
• Often a 10 degree temp increase means the rate doubles- linear relationship

Catalysts:

• A substance that increases the rate of a reaction but isnt used up in the reaction
• They lower the activation energy needed so the frequency of collisions increases

Catalysts can be used in: Biological washing powders, Medicine, Biodiesel, Cars, Slimming/ Baby food

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## Factors affecting Rates of Reaction

Concentration:

• Dilute solution: a small amount of solute in a given amount of solution
• Concentrated solution: a large amount of solute in a given amount of solution
• The units of concentration are mol/dm
• When the concentration/ pressurre are higher, the rate is faster because the frequency of collisions is higher

To calculate the rate of reaction from a graph you divide the time by the amount of product made

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