Question

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

Answer 1

Hint: Positive catalysts increase the rate of reaction and decrease the activation energy, whereas negative catalysts slow down the reaction to complete.

Complete answer:
In order to answer our question, we need to know about catalysts. Every chemical reaction has a specific rate, some reactions occur fast, like the reaction of sodium with water, whereas some reactions occur very slowly, like the rusting of iron. Catalysts are these substances which when added in the reaction changes the rate of the reaction, it can either make it fast or slow. However, the catalyst itself does not get consumed as the reaction proceeds. Catalysts exist in solid, liquid as well as gaseous forms.
Now, let us come to the question.
Catalysts also change the activation energy of the reaction. Positive catalysts are those catalysts which increase the rate of the reaction This means that the activation energy of the reaction is lowered, and the speed of the reaction also increases. An example of positive catalysis is decomposition of potassium chlorate. Without a catalyst, decomposition takes place at ${{700}^{0}}C$, and with an MnO catalyst, decomposition takes place at ${{300}^{0}}C$.
\[KCl{{O}_{3}}\xrightarrow{MnO}KCl+{{O}_{2}}\]
Negative catalysts are opposite of the positive catalysts. They decrease the overall rate of the chemical reaction. An example of a negative catalyst is phosphoric acid, which can be used to decrease the rate of hydrogen peroxide decomposition.
\[{{H}_{2}}{{O}_{2}}\xrightarrow{{{H}_{3}}P{{O}_{4}}}{{H}_{2}}O+{{O}_{2}}\]
Catalysts create an alternative path for the reaction to occur, hence they are responsible for changing reaction rates.

Note:
Catalysis occurs in nature as well as in the human body. We have catalysts in the form of enzymes, which help us in the digestion of food.