Question

The formation of water from ${{H}_{2}}(g)$ and ${{O}_{2}}(g)$ is an exothermic process because:
[A] The chemical energy of ${{H}_{2}}(g)$ and ${{O}_{2}}(g)$ is more than that of water.
[B] The chemical energy of ${{H}_{2}}(g)$ and ${{O}_{2}}(g)$ is less than that of water.
[C] The temperature of ${{H}_{2}}(g)$ and ${{O}_{2}}(g)$ is higher than that of water.
[D] The temperature of ${{H}_{2}}(g)$ and ${{O}_{2}}(g)$ is lower than that of water.

Answer 1

Hint: A chemical reaction which releases heat on moving in the forward direction is called an exothermic reaction. A reaction is exothermic if the total energy of the product is less than that of the reactants.

Complete answer:
We know that a process which increases the temperature of the surroundings by releasing heat in the form of energy is known as an exothermic reaction.
When we add two reactants to get a particular product out of it, there is a reaction taking place between the reactants. This reaction is either endothermic i.e. to move forward and give us the product it will require some sort of energy which is generally in the form of heat or sometimes light if not endothermic, the reaction is exothermic which means it proceeds forward by releasing energy in the surrounding. This energy is released in the form of heat.
In thermodynamics, we describe this energy by the term enthalpy. Enthalpy is the change in internal energy of the reaction. Enthalpy is written in terms of internal energy, pressure and volume but considering only the internal energy part, we can write enthalpy as-
     \[\Delta H=U(product)-U(reactant)\]
Where, U stands for internal energy.
If the total internal energy of the product is higher, enthalpy is positive which means the reaction is endothermic and if the internal energy of the reactant is higher than the product, enthalpy is negative and the reaction is exothermic.
It is given to us that formation of water from hydrogen and oxygen gas is exothermic, which means the energy of the reactant is higher than that of the products.

Therefore, the correct answer is option [A] the chemical energy of ${{H}_{2}}(g)$ and ${{O}_{2}}(g)$ is more than that of water.

Note: We cannot form water by combining hydrogen and oxygen directly. Water is prepared from hydrogen and oxygen through electrolysis. Mixing hydrogen and oxygen as a chemical and not an electrochemical reaction will give us hydrogen peroxide.