IGCSE Chemistry: Rates of Reaction

What is rate of reaction?

How fast the reactants are changed into products in a chemical reaction.

How would you ​investigate​ ​the​ ​effects​ ​of​ ​changes​ ​in​ ​surface area​ ​of​ ​a​ ​solid,​ ​concentration​ ​of​ ​a​ ​solution,​ ​temperature​ ​and​ ​the​ ​use​ ​of​ ​a catalyst​ ​on​ ​the​ ​rate​ ​of​ ​a​ ​reaction?

You can use equations to find the rate of reaction to compare the effect of changes in surface area, concentration, temperature, use of a catalyst etc.

Rates of reactions can be measured using the amount of product used, or amount of product formed over time.

Describe the effects of changing the surface area of a solid on the rate of reaction.

Increasing the surface area of solid reactants increases the rate of reaction, as it increases the frequency of collisions.

Describe the effects of changing the concentration of a solution on the rate of reaction.

Increasing concentration of reacting solutions increases the rate of reaction, as it increases the frequency of collisions.

Describe the effects of changing the pressure of a gas on the rate of reaction.

Increasing pressure in reacting gases increases the rate of reaction, as it increases the frequency of collisions.

Describe the effects of changing the temperature on the rate of reaction.

Increasing the temperature increases the rate of reaction.

As increasing temperature increases the speed of the moving particles, they collide more frequently and energetically.

Describe the effects of the use of a catalyst on the rate of reaction.

Catalysts speed up chemical reactions.

What is a catalyst?

A substance that speed up chemical reactions without being changed or used up during the reaction.

How do catalysts work?

Catalysts provide an alternative pathway for a chemical reaction with a lower activation energy.

This increases the proportion of particles with energy to react.

On a reaction profile diagram, would the reactant line be higher or lower than the product line?

Higher

Would the activation energy on a reaction profile diagram be higher or lower when a catalyst is used?

Lower

​Describe the effect​​ of​​ changing​​ the​​ surface​​ area​​ of​​ marble chips​​ ​on​ the​ ​rate​ ​of reaction​ ​between​ ​marble​ ​chips​​ and​ ​dilute​ hydrochloric​​ acid.

Using smaller marble chips (larger surface area), you should see an increase in reaction rate.

​Describe the effect​​​​ of​ changing​ ​the​ ​concentration​ of​ ​hydrochloric​ ​acid​ ​on​ the​ ​rate​ ​of reaction​ ​between​ ​marble​ ​chips​​ and​ ​dilute​ hydrochloric​​ acid.

Increasing the concentration of hydrochloric acid should increase the reaction rate.