Ncert Exercises & Solutions

The enthalpy of sublimation of a substance is equal to-

1. Enthalpy of fusion + Enthalpy of vaporisation

2. Enthalpy of fusion

3. Enthalpy of vaporisation

4. Twice the enthalpy of vaporisation

Hint: Sublimation reaction in which solid substsnce directly convert into gas formed.

Step 1:

Sublimation process is a direct conversion of solid to vapour; solid

\to

vapour

Standard enthalpy of sublimation is the change in enthalpy when one mole of a solid substance sublimes at a
constant temperature and under standard pressure (1bar).

Step 2:

The sublimation process occurs in two steps, we have solid

\to

liquid

\to

vapour

solid

\to

liquid requires enthalpy of fusion and liquid

\to

vapour requires enthalpy of vaporisation.

Hence, Enthalpy of sublimation of a substance is equal to Enthalpy of fusion + Enthalpy of vaporisation

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