Question

Give an example of a reaction in which gas evolves.

Answer 1

Hint: These reactions are known as gas evolution reactions. There are different types of gases evolved in such reactions most commonly these gases are carbon dioxide, hydrogen gas and water. The simplest gas evolution reaction is a combustion reaction with the evolution of carbon dioxide gas.

Complete answer:
The chemical reaction in which one of the end products is a gas such as hydrogen, oxygen, or carbon dioxide is known as gas evolution reactions. In some cases the gas evolved may be poisonous; these reactions are carried out in a fume chamber to prevent any kind of physical damage by inhalation of the gas or even explosion.
Many reactions take place with the evolution of a gas. One of them is when nitric acid reacts with sodium carbonate to form sodium nitrate, carbon dioxide, cyanide, Sulphur dioxide, ammonia, hydrogen sulfide and water. So the gas evolved in this reaction is carbon dioxide. The reaction takes place in the following manner:
\[2HN{O_{3}}(aq) + N{a_{2}}C{O_{3}}(aq) \to 2NaN{O_{3}}(aq) + C{O_2}(g) + {H_2}O(l)\]
There are many examples of gas evolution reactions. When a metal undergoes oxidation in an acidic solution then salt is produced along with the evolution of hydrogen gas. When limestone reacts with hydrochloric acid then carbon dioxide gas is evolved, like this, there are many such reactions. These are some specific reactions in which every time the reaction occurs there is an evolution of gas. These reactions are- combustion reactions, single replacement reactions, decomposition reactions, acid-base reactions, and redox reactions.

Note:
It might become hard to identify which reactions are gas evolution reactions but with a couple of points it can become easy to identify these reactions. Carbonates and bicarbonate form compounds that break down into gases, sulfides tend to create gas products, ammonium compounds can form compounds that break down to give ammonia gas, and so on.