The enthalpy change for sublimation (solid to gas) is what?

The enthalpy change for sublimation (solid to gas) is what?

• A. Negative
• B. Zero
• C. Indeterminate
• D. Positive

Answer: (D)

Sublimation is an endothermic process where a solid becomes a gas, so energy must be absorbed. The enthalpy change for sublimation is positive because you’re adding heat to overcome the forces holding the solid together and to form gas molecules. In terms of enthalpy, ΔH_sub is effectively the sum of the enthalpies of fusion and vaporization, both of which are positive, so their sum is positive. An example is dry ice subliming at room temperature as it absorbs heat. So, the enthalpy change for sublimation is positive.

Sublimation is an endothermic process where a solid becomes a gas, so energy must be absorbed. The enthalpy change for sublimation is positive because you’re adding heat to overcome the forces holding the solid together and to form gas molecules. In terms of enthalpy, ΔH_sub is effectively the sum of the enthalpies of fusion and vaporization, both of which are positive, so their sum is positive. An example is dry ice subliming at room temperature as it absorbs heat.

So, the enthalpy change for sublimation is positive.