Question

The number of moles of hydrogen molecules required to produce 20 moles of ammonia through Haber’s process is:
(A) 10
(B) 20
(C) 30
(D) 40

Answer 1

Hint: A convenient method of expressing the amount of substance is the mole concept. A pure element will contain a huge number of atoms when dealing with particles at the molecular level required for this mole concept. According to this mole concept, a mole is a count of a very large number of particles.

Complete step by step solution:
The amount of substance that contains exactly $6.023\times {{10}^{23}}$ elementary entities of a given substance is known as mole. The elementary entities which can be represented in moles of atoms, molecules, monatomic or polyatomic ions.
The number of moles in a sample of an element or compound can be calculated by the ratio of the total mass of the sample to the molar mass of the element or compound as described by the following formula,
Number of moles = (mass of the sample)/ (molar mass)
The given reaction is a Haber’s process,
${{N}_{2}}(g)+3{{H}_{2}}(g)\rightleftharpoons 2N{{H}_{3}}(g)$
From the above reaction, 3moles of hydrogen are required to produce 2moles of ammonia.
Therefore, $\dfrac{3}{2}$ moles of hydrogen required to produce 1 mole of ammonia
To produce 20 moles of ammonia, $\dfrac{3}{2}\times 20=30$ moles of hydrogen needed.
Hence, 30moles of hydrogen molecules are required to produce 20 moles of ammonia through Haber’s process.

The correct answer is option C.

Note: Sometimes the number of moles of its constituent elements may not always be equal to the number of moles of a molecule. The total number of molecules or atoms in a sample can be calculated by the number of moles multiplying with Avogadro number.