Question

C. What predictions can you make about ΔH, ΔS, and ΔG for the general reaction A(s) + 2B(g) 3C(g) + D(g) + heat? What conclusions can you make about the spontaneity of the reaction? Explain your reasoning. (4 points)

d. The reaction 2NO2(g) N2(g) + 2O2(g) is spontaneous at all temperatures, yet it hardly happens under normal conditions. How can this be? (2 points)

Answer 1

C.

1) Entropy (∆S) is spontaneous

2) Enthalpy (∆H) is not spontaneous

3) Gibbs free energy (∆G) is spontaneous

Therefore the reaction will be spontaneous at high temperature.

D.

Because Nitrogen is favourable to be produced under high temperature, and oxygen under low temperature. Which favours the product side of the equation. But when at a room temperature, which means the temperature is neither low nor high, the product side won't be favoured, and the reaction will not be spontaneous.

EXPLANATION:

C.

1) Entropy is the measure of disorderliness in a system, which increase more in gaseous substances, because the molecules of gases are not stable

Because almost all the reacting substances are in their gaseous state, the entropy of the reaction will be high. Therefore entropy will be positive, which makes the entropy of the system spontaneous.

2) Enthalpy is the measure of heat change in the system. Since their is an intake of heat in the system, therefore the reaction is endothermic and ∆H will be positive. Enthalpy of a system can only be spontaneous in an Exothermic reaction, where ∆H is negative. Therefore Enthalpy is not spontaneous.

3) Gibbs free energy is equal to the change in enthalpy minus the product of temperature and change in entropy. Since entropy and enthalpy are positive, the Gibbs free energy will be negative, which shows that the reaction can be spontaneous if some conditions are met. ∆G will be spontaneous because it is negative.

Therefore in summary, the reaction will favour the product side more, if the temperature of the system is increased, which will make the reaction to become more spontaneous.

D.

2NO2(g) --> N2(g) + 2O2(g)

This reaction is not spontaneous under atmospheric pressure and room temperature (normal conditions) because, Nitrogen can only be produced very fast at a high temperature, while oxygen production is preferable in a low temperature. For the reaction to favour the product side, the temperature should be increased or decreased. Because an increase or a decrease in the temperature will favour either nitrogen or oxygen, which are the product side of equation. This means that the reaction should not be spontaneous if you wish to achieve an equal proportion of the products.