Reaction Feasibility (CIE A Level Chemistry)

• The Gibbs equation can be used to calculate whether a reaction is feasible or not

ΔG^ꝋ = ΔH_reaction^ꝋ - TΔS_system^ꝋ

• When ΔG^ꝋ is negative, the reaction is feasible and likely to occur
• When ΔG^ꝋis positive, the reaction is not feasible and unlikely to occur

Answer

• Step 1: Calculate ΔS_system^ꝋ

ΔS_system^ꝋ = ΣΔS_products^ꝋ - ΣΔS_reactants^ꝋ

ΔS_system^ꝋ = (2 x ΔS^ꝋ [CaO(s)]) -  (2 x ΔS^ꝋ [Ca(s)] + ΔS^ꝋ [O₂(g)])

= (2 x 40.00) - (2 x 41.00 + 205.0)

= -207.0 J K^-1 mol^-1

• Step 2: Convert ΔS^ꝋ to kJ K^-1 mol^-1

= -0.207

• Step 3: Calculate ΔG^ꝋ

ΔG^ꝋ = ΔH_reaction^ꝋ - TΔS_system^ꝋ

= -635.5 - (298 x -0.207)

= -573.8 kJ mol^-1

• Step 4: Determine whether the reaction is feasible

  Since the ΔG^ꝋ is negative the reaction is feasible and likely to occur