Question

When nitrogen reacts with hydrogen under high temperature and pressure, ammonia, which is also a gas, is formed. this is an example of:
(A)- Chemical combination
(B)- Chemical decomposition
(C)- Physical change
(D)- None of these

Answer 1

In the given process, it is seen that a single product, that is, ammonia is formed by the reaction of two compounds under specific conditions of temperature and pressure.

Complete step by step answer:
The given reaction is commonly known as the Haber process, used for the production of ammonia gas. It takes place by the reaction of atmospheric nitrogen gas and the hydrogen gas obtained from naturally-occurring methane gas in presence of a catalyst, forming the ammonia gas.
${{N}_{2}}(g)+3{{H}_{2}}(g)\rightleftarrows 2N{{H}_{3}}(g)+\Delta \,(heat)$
The catalyst mainly used is the Fe metal along with the promoter (molybdenum) which enables the unreactive nitrogen gas by breaking its triple bond and accelerating the reaction.
It is an exothermic reaction, as heat is released on the formation of ammonia gas. It is a reversible reaction.
During the chemical process, a new compound is synthesised from the two reactant substances. Thus, it is a chemical combination or synthesis reaction.
Since, all the three substances are present in a gaseous state. So, there is no physical change during the reaction process.

Therefore, the given chemical process is an example of option (A)- Chemical combination.

Note: In this process, utmost care must be taken of the temperature and pressure condition, as it affects the yield of the ammonia, the rate of reaction and the overall cost of production.
- A temperature of ${{450}^{\circ }}C$is chosen because at temperature lower than this, the rate is slow and at higher temperature the equilibrium shifts towards the left (endothermic) of the reaction.
- A pressure of 200 atm is chosen because at high pressure it favours the right side of the reaction. But it is quite expensive to maintain apparatus for higher pressures.