Question

The conversion of atomic hydrogen into ordinary hydrogen is
A. Exothermic change
B. Endothermic change
C. Nuclear change
D. Photochemical change

Answer 1

Hint: Atomic hydrogen is transformed into common hydrogen through an exothermic process. Since hydrogen molecules are extremely stable and hydrogen atoms are relatively unstable, they join easily to produce hydrogen molecules, which are highly stable and release energy.

Complete Step by Step Answer:
The hydrogen that exists alone is active hydrogen. It is an atomic hydrogen that only exists as a single hydrogen atom, not as a hydrogen molecule. It has a strong tendency to react. Additionally, it is known as "active hydrogen" due to its high level of reactivity.
Ordinary hydrogen means the molecular hydrogen, it’s been called so because the hydrogen molecule exists in a diatomic state and it’s the most common state in which the hydrogen gas is present.

An exothermic process occurs when atomic hydrogen is transformed into regular hydrogen. Atomic hydrogens are extremely unstable and have surplus energy; as a result, when they unite to create a stable molecule with low energy, the extra energy is released as heat. This makes the reaction exothermic.
\[2H\to {{H}_{2}};\Delta H=104.5kcal\]
Hence, the correct option is A. Exothermic change

Additional information: Exothermic reactions are chemical in nature and are distinguished by the release of energy in the form of heat or light. One instance of this kind of reaction, when the release is in the form of both heat and light, is lighting a match. The exothermic reaction results in the release of energy as opposed to an endothermic reaction, which absorbs energy. This energy frequently exceeds the sum of the energies of the reactants. In the matchstick example from above, the flame that results from a match produces more energy than the matchstick's potential energy.

Note: When formulating the chemical equation for an endothermic reaction, the energy is written on the reactant side and the enthalpy change for the reaction is positive. The exothermic process has a negative change in enthalpy. For an exothermic process, the energy is recorded on the product side. The thermodynamic word for measuring energy is enthalpy.