Factors Affecting Reaction Rates

Rates of chemical reactions do not all proceed at the same pace. Some are very slow and others are fast. For example,

• Burning methane is fast
• Rusting of iron is slow.

In fact, the same chemical reaction can proceed at vastly different rates based on the conditions in which it takes place. There are five factors that will influence the reaction rate.

• Temperature
• Concentration
• Pressure
• Surface Area
• Catalyst

Watch the following video!

https://youtu.be/OttRV5ykP7A

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Temperature

Increased temperature will increase the reaction rate.  This is because when temperature is increased, the speed of the molecules is increased, giving them more kinetic energy.  This means there will be more, and higher energy collisions, allowing more collisions to collide with energy above the activation energy threshold. For example,

• Glow sticks and other items, such as mood rings, change color based on temperature.
  
• Factors such as temperature speed up or slow down the chemical reactions involved in cooking. At high heat, you can cook an egg faster than at lower heats.

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Concentration

Reaction rates of systems change as the concentration of the reactants change. A higher concentration of reactants means there are more reactants in a given area and less spaces between the reactants, so more collisions will occur. If there are more collisions then the total number of effective collisions will increase which will result in more products (faster reactions).

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Pressure

According to Boyle's Law, as the pressure increases, the volume decreases. When the pressure increases, the particles are forced into a smaller, more confined space, and the number of collisions would increase. An increase in the number of collisions results in an increase in the number of effective collisions which increases the rate at which products form.

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Surface Area

Which dissolves faster in a cup of hot tea, a sugar cube or a teaspoon of granular sugar?

• Answer: Granular Sugar
  

Which burns faster, a lump of coal or several small pieces?

• Answer: several small pieces

The more surface area the reactant has, the more the reactant is exposed for the collisions to occur, and the frequency of particle collisions increases. Therefore, the change for effective collisions increase and the reaction rate increases.

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Catalyst

A catalyst will speed up the reaction rate significantly, but a catalyst is not a product or reactant. Catalyst's are used to lower the activation energy required for a reaction to occur.

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Let's Review

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Inhibitor

When you want to slow down a reaction, you can use an inhibitor. An inhibitor causes a chemical reaction to proceed more slowly. By adding an inhibitor, you are preventing a chemical reaction from occurring. For example, inhibitors are added to food to increase their shelf life by preventing or slowing reactions that cause foods to spoil.