Rate of Reaction: Answers

Define the term ‘activation energy’.

The activation energy for a reaction is the minimum amount of energy needed for the molecules to react.

Why does an increase in temperature result in a faster reaction rate?

An increase in temperature gives the reacting molecules more kinetic energy. Since they are moving faster, they are more likely to collide. More frequent collisions means a faster rate of reaction.

Increasing the temperature also gives the reacting molecules more energy. The reactants are more likely to exceed the activation energy which means there will be more successful collisions.

How does a catalyst work to speed up the rate of a reaction?

A catalyst speeds up the rate of reaction by providing an alternative reaction pathway with a lower activation energy. This means that a higher proportion of reacting molecules will have more than the activation energy so there will be more successful collisions.

Magnesium reacts with water to form magnesium hydroxide and hydrogen gas. Describe two ways in which the rate of reaction can be investigated.

Since a gas is given off we can use one of two methods: the weighing balance method or the gas syringe method. The first method involves placing the reactants in a conical flask and placing the flask on top of a measuring balance. The gas that escapes from the flask will cause the mass of the flask to decrease. When the mass stops decreasing, the reaction is complete. The change in mass divided by the time taken will give you the reaction rate.

The other method involves connecting the conical flask to a gas syringe. The gas given off will be collected in the gas syringe. The volume of gas inside the syringe is divided by the time taken to calculate the reaction rate.