Question

When a solid directly turns into gaseous change, it is called:
(A) Sublimation
(B) Condensation
(C) Polymerization
(D) Melting

Answer 1

We know that a change of state usually takes place by heating or cooling. Like if a solid is changing into a liquid it is mainly because of heating while if we’ll cool the liquid it will again change into solid. There is a process which directly converts solid into gaseous change which happens due to heating.

Complete step-by-step answer:
The process in which a solid directly changes into a gaseous state is known as sublimation and the amount of heat energy required to convert a mole of solid directly into the gaseous state at constant pressure is known as the molar enthalpy of sublimation. The enthalpy of sublimation is usually expressed as $\Delta {H_{sub}}$ in joules per mole or kilogram of a substance.As we know that a solid cannot be directly converted into gaseous state without passing through an intermediate state i.e., liquid state.So, this process of sublimation takes place in two steps.
In the first step:$Solid \to liquid$
The process in which a solid is converted into the liquid state is known as melting or we can also say that the heat energy required to change one mole of a solid to liquid state without any change in temperature is known as the latent heat of fusion also known as the enthalpy of fusion.
In the second step:$liquid \to gaseous$
So, the process in which a liquid is converted into gaseous state is known as vaporization or the heat energy required to change one mole of liquid at its boiling point to gaseous state is known as latent heat of vaporization also known as enthalpy of vaporization.

Hence the correct answer is (A).

Note: Here we have used the term latent heat because latent heat is the energy which can be absorbed or released by a substance, the pressure and temperature remaining constant during the process. Also, the heat of vaporization is always greater than the heat of fusion because there is a large separation of particles in gaseous state so more energy will be required to change a liquid into a gas.