Calculate the standard Gibbs free energy change () for the displacement reaction: . The standard fre — Thermodynamics and Thermochemistry Chemistry Question
Question
Calculate the standard Gibbs free energy change ($\Delta_r G^\circ$) for the displacement reaction: $CH_4(g) + 2Cl_2(g) \rightarrow CCl_4(l) + 2H_2(g)$. The standard free energies of formation ($\Delta_f G^\circ$) for $CH_4(g)$ and $CCl_4(l)$ are -50.75 and -65.27 kJ/mol respectively.
Answer: A
💡 Solution & Explanation
The free energy of formation for elements in their standard reference states ($Cl_2(g)$, $H_2(g)$) is strictly zero. By Hess's Law: $\Delta_r G^\circ = \sum \Delta_f G^\circ(products) - \sum \Delta_f G^\circ(reactants) = [-65.27 + 2(0)] - [-50.75 + 2(0)] = -65.27 + 50.75 = -14.52$ kJ/mol.
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