Question

 What are (i) positive catalysts and (ii) negative catalysts? Support your answer with one example for each of them.

Answer 1

 (i) Positive catalyst: When a catalyst increases the rate of chemical reaction, it is called positive catalyst.
e.g. when potassium chlorate heated to 700°C decomposes to evolve oxygen gas, when MnO₂is added the decomposition takes place at 300°C
\[\ce{2KCIO3->[MnO2][300°C] 2KCl + 3O2}\]
(ii) Negative catalyst: When a catalyst decreases the rate of chemical reaction it is called negative catalyst.
Example. Phosphoric acid acts as a negative catalyst to decrease the rate of the decomposition of hydrogen peroxide. Alcohol too acts as a negative catalyst in certain chemical reactions.