Learning Objective

In this lesson we will learn how the rate of a chemical reaction is affected by the following factors: temperature, concentration, pressure, surface area, stirring and catalysts.

Learning Outcomes

By the end of this lesson you will be able to:

  • Explain how temperature affects the rate of a chemical reaction.
  • Explain how concentration of solutions affects the rate of a chemical reaction.
  • Explain how pressure of gases affects the rate of a chemical reaction.
  • Explain how surface area of solids and liquids affects the rate of a chemical reaction.
  • Explain how stirring affects the rate of chemical reactions involving heterogeneous mixtures.
  • Explain how catalysts affect the rate of a chemical reaction.

Factors that Affect Rate of Reaction

1 | Manipulating Reaction Rate

2 | Effect of Temperature on Reaction Rate

3 | Effect of Concentration and Pressure on Reaction Rate

4 | Effect of Surface Area on Reaction Rate

5 | Effect of Stirring on Reaction Rate

6 | Effect of Catalysts on Reaction Rate

7 | Summary

 

 factors that affect rate of reaction worksheet  year 10 chemistry pdf workbook  Year 10 Chemistry Print Workbook Australian Curriculum

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Manipulating Reaction Rate

  • Based on collision theory, the rate of a chemical reaction depends on:
  • The frequency of collisions between reactant particles.
  • The energy of collisions between reactant particles.
  • The orientation of collisions between reactant particles.
  • Consequently, anything that influences any of these three factors will affect reaction rate.
  • The main factors that can influence the rate of a chemical reaction are:
  • Temperature of reaction.
  • Concentration or pressure of reactants.
  • Surface area of reactants.
  • Stirring of reaction.
  • Presence of catalysts.

 
particle collisions reaction rate

Any factor that affects the frequency of successful particle collisions will affect reaction rate.

 


Effect of Temperature on Reaction Rate

 

Effect

  • An increase in temperature will lead to an increase in reaction rate.

 
temperature reaction rate

An increase in temperature leads to an increase in reaction rate.

 

Reason

  • An increase in temperature means that reactant particles move faster and have more energy.
  • An increase in the movement of reactant particles will result in more frequent collisions.
  • An increase in the energy of reactant particles means that there will be a greater proportion of successful collisions – that is, collisions will more likely involve sufficient energy to break bonds.
  • These two factors will consequently increase the rate of reaction.

 

Examples

  • Magnesium reacts more vigorously with water when heated over a Bunsen burner.
  • The industrial production of nitric acid is performed at high temperature to increase the rate of reaction and therefore the efficiency of production.
  • The cold temperatures of fridges and freezers reduces the rate of food spoilage.

 

 temperature test tube bunsen flame increased rate of reaction  food fridge freezer decreased rate of reaction

Heating test tubes over a Bunsen burner increases the rate of chemical reactions.
By decreasing temperature, fridges and freezers slow down the spoilage of food.

(Images: Tim, Adobe Stock; 27707, Pixabay)

 


Effect of Concentration and Pressure on Reaction Rate

 

Effect

  • An increase in concentration of solutions will lead to an increase in reaction rate.

 
concentration reaction rate

An increase in concentration leads to an increase in reaction rate.

 

  • An increase in pressure of gases will lead to an increase in reaction rate.

 
pressure reaction rate

An increase in pressure leads to an increase in reaction rate.

 

Reason

  • An increase in concentration of solutions or pressure of gases means there are more reactant particles in a given space.
  • More particles in a given space will result in more frequent collisions.
  • This will consequently increase the rate of reaction.

 

Examples

  • Acids that have a higher concentration react more vigorously with other substances.
  • Gases stored under high pressure are more explosive when ignited.
  • The industrial production of ammonia is performed at high pressure to increase the rate of reaction and therefore the efficiency of production.

 

 concentration acid solution reaction rate  pressure gas reaction rate

Concentrated acids react more vigorously than dilute acids.
Industrial reactions involving gases are performed at high pressure.

(Images: Forance, Adobe Stock; Sharon Loxton, Wikimedia Commons)

 


Effect of Surface Area on Reaction Rate

 

Effect

  • An increase in surface area of solids or liquids will lead to an increase in reaction rate.

 
surface area reaction rate

An increase in surface area leads to an increase in reaction rate.

 

Reason

  • An increase in surface area of solids or liquids in heterogeneous reaction mixtures means that more reactant particles are exposed.
  • Greater exposure of reactant particles will result in more frequent collisions.
  • This will consequently increase the rate of reaction.

 

Examples

  • A steel bar will not burn when placed in a flame but steel wool will burn readily.
  • Dust in flour mills and coal mines can be a serious safety issue as it is highly flammable, whereas grain and coal do not ignite readily.
  • Fuel injectors create a fine mist from liquid fuels, enabling efficient combustion in car engines.

 

 surface area flour dust explosion  surface area fire breathing

Increasing the surface area of solids (left) and liquids (right) allows them to burn much more easily.

(Images: Hans-Peter Scholz, Wikimedia Commons; TVR, Wikimedia Commons)

 


Effect of Stirring on Reaction Rate

 

Effect

  • Stirring heterogeneous reaction mixtures will lead to an increase in reaction rate.

 
stirring reaction rate

Stirring heterogeneous reaction mixtures leads to an increase in reaction rate.

 

Reason

  • Stirring or agitating a heterogeneous reaction mixture means that more reactant particles are exposed.
  • Greater exposure of reactant particles will result in more frequent collisions.
  • This will consequently increase the rate of reaction.

 

Examples

  • Many industrial food and chemical processes, such as fermentation reactions, are carried out in large batch reactors that use stirrers to continually agitate the reaction mixture.

 
stirring industrial agitator reaction rate

Large industrial agitators are commonly used for stirring heterogeneous reaction mixtures.

(Image: Yuri Raysper, Wikimedia Commons)

 


Effect of Catalysts on Reaction Rate

 

Effect

  • The presence of catalysts will lead to an increase in reaction rate.

 
catalyst reaction rate

The presence of a catalyst leads to an increase in reaction rate.

 

Reason

  • Catalysts are substances that lower the energy required to break bonds (activation energy), by orienting reactant molecules in a way that makes bonds easier to break.
  • Lower activation energy means a greater proportion of successful collisions between reactant particles.
  • This will consequently increase the rate of reaction.
  • Some reactions do not proceed at all without a catalyst.
  • Catalysts increase the rate of a chemical reaction, but are not themselves changed during the reaction.
  • A catalysed reaction is written as:

catalysed chemical reaction

  • This shows that the reaction takes place in the presence of a catalyst, and that the catalyst is neither a reactant nor a product.

 

Examples

  • Hydrogen peroxide breaks down slowly if left on the shelf, but in the presence of manganese dioxide catalyst, it breaks down rapidly.
  • A platinum catalyst enables the rapid reaction between hydrogen and oxygen in fuel cells.
  • Most chemical reactions that take place in living things require specialised biological catalysts called enzymes, otherwise they would not proceed.

 
catalyst hydrogen fuel cell

Platinum catalysts are used to increase the efficiency of hydrogen fuel cells.

(Image: Luigi Bertello, Adobe Stock)

 


Summary

  • The rate of a chemical reaction is largely determined by the chemical properties of the reactants, but is also affected by factors that influence either of the following:
  • The frequency of particle collisions.
  • The proportion of particle collisions that are successful.
  • An increase in temperature will lead to an increase in reaction rate.
  • Reactant particles move around more, resulting in a greater frequency of collisions.
  • Reactant particles have more energy, resulting in a greater proportion of collisions with sufficient energy to break bonds.
  • An increase in the concentration of solutions or pressure of gases will lead to an increase in reaction rate.
  • More reactant particles are in a given space, resulting in a greater frequency of collisions.
  • An increase in the surface area of solids or liquids in heterogeneous reaction mixtures will lead to an increase in reaction rate.
  • More reactant particles are exposed to collisions, resulting in a greater frequency of collisions.
  • Stirring of heterogeneous reaction mixtures will lead to an increase in reaction rate.
  • More reactant particles are exposed to collisions, resulting in a greater frequency of collisions.
  • The presence of catalysts will lead to an increase in reaction rate.
  • The energy required to break bonds is lowered, resulting in a greater proportion of collisions with sufficient energy to break bonds.

 
thermite chemical reaction rate

(Image: CaesiumFluoride, Wikimedia Commons)

(Header image: NASA, Wikimedia Commons)

 


 

 factors that affect rate of reaction worksheet  year 10 chemistry pdf workbook  Year 10 Chemistry Print Workbook Australian Curriculum

Click images to preview the worksheet for this lesson and the Year 10 Chemistry Workbook (PDF and print versions)