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JAMB Chemistry 2014 Paper

Question : 24

Total: 45

Solution:

Concept:

The relationship between free energy change, enthalpy change, and entropy change is given by

\Delta G = \Delta H - T\Delta S

Explanation:

Convert the temperature from Celsius to Kelvin:

T = 25^\circ\mathrm{C} + 273 = 298\,\mathrm{K}

Given:

\Delta G = -899\,\mathrm{J\,mol^{-1}}

and

\Delta S = 10\,\mathrm{J\,mol^{-1}\,K^{-1}}

Calculate

T\Delta S

T\Delta S = 298 \times 10 = 2980\,\mathrm{J\,mol^{-1}}

Rearrange the equation to find

\Delta H

\Delta H = \Delta G + T\Delta S

Substitute the values:

\Delta H = -899 + 2980 = +2081\,\mathrm{J\,mol^{-1}}

Answer:

\Delta H = +2081\,\mathrm{J\,mol^{-1}}

, so the correct option is A. +2081 Jmol^-1.

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