Everything Science Grade 12

3.5 CHAPTER 3. REACTION RATES

DEFINITION: Catalyst

A catalyst speeds up a chemical reaction, without being altered in any

way. It increases the reaction rate by lowering the activation energy for

a reaction.

Energy diagrams are useful to illustrate the effect of a catalyst on reaction rates. Cat-
alysts decrease the activation energy required for a reaction to proceed(shown by the
smaller ’hump’ on the energy diagram in figure 3.5), and therefore increase the reaction
rate.

activated complex

products

reactants

activation

energy

activation energy

with a catalyst

Time

Potential energy

Figure 3.5: The effect ofa catalyst on the activation energy of a reaction

Activity: Catalysts and reaction rates

Aim:

To determine the effectof a catalyst on the rateof a reaction

Apparatus:

Zinc granules, 0.1 M hydrochloric acid, copperpieces, one test tube and a

glass beaker.

Method:

1. Place a few of the zinc granules in the test tube.


2. Measure the mass ofa few pieces of copper and keep them separate from
   the rest of the copper.


3. Add about 20 cm^3 of HCl to the test tube. You will see that a gas is
   released. Take note of how quickly or slowly this gas is released. Writea
   balanced equation for the chemical reaction thattakes place.