Without doing any calculations, determine the signs of ΔS_sys and...

Question

Without doing any calculations, determine the signs of ΔS_sys and ΔS_surr for each chemical reaction. In addition, predict under what temperatures (all temperatures, low temperatures, or high temperatures), if any, the reaction is spontaneous. a. 2 CO(g) + O2(g) → 2 CO2(g) ΔH_rxn° = -566.0 kJ b. 2 NO2(g) → 2 NO(g) + O2(g) ΔH_rxn° = +113.1 kJ c. 2 H2(g) + O2(g) → 2 H2O(g) ΔH_rxn° = -483.6 kJ d. CO2(g) → C(s) + O2(g) ΔH_rxn° = +393.5 kJ

Accepted Answer

For each reaction, determine the sign of $$ \Delta S_{sys}  by $$considering the change in the number of moles of gas. If the number of moles of gas increases, $$ \Delta S_{sys}  is $$positive; if it decreases, $$ \Delta S_{sys}  is $$negative..  For each reaction, determine the sign of $$ \Delta S_{surr} $$ using the sign of $$ \Delta H_{rxn}^\circ . If$$ $$ \Delta H_{rxn}^\circ  is $$negative (exothermic), $$ \Delta S_{surr}  is $$positive; if $$ \Delta H_{rxn}^\circ  is $$positive (endothermic), $$ \Delta S_{surr}  is $$negative..  Use the Gibbs free energy equation $$ \Delta G = \Delta H - T \Delta S  to $$predict spontaneity. A reaction is spontaneous when $$ \Delta G  For exothermic reactions (negative \( \Delta H_{rxn}^\circ $$), if $$ \Delta S_{sys}  is $$negative, the reaction is spontaneous at low temperatures. If $$ \Delta S_{sys}  is $$positive, the reaction is spontaneous at all temperatures..  For endothermic reactions (positive $$ \Delta H_{rxn}^\circ $$), if $$ \Delta S_{sys}  is $$positive, the reaction is spontaneous at high temperatures. If $$ \Delta S_{sys}  is $$negative, the reaction is non-spontaneous at all temperatures.

Key Concepts

Entropy (ΔS)

Enthalpy (ΔH) and Spontaneity

Gibbs Free Energy (ΔG)