Predict with reason, whether the entropy change for this reaction will pe positive, neagtive or neglibly small

Question

Reaction is:

2NO(g) + O2 (g) --> 2NO2 (delta H = -114kJ)

Also it asked:

Using the relationship between free energy change, enthalpy change and entropy change for a reaction, explain why that reacttion is less energetically favoured at high temperatures.

Please help cause I neve gothang of these and this is summer HW so I can't ask my teacher. Thanks

Answer 1

3 moles of gas go to 2 moles - so it has a negative entropy change.

If the reaction is exothermic, and the entropy is also negative, raising the temperature (according to DG = DH - TDS) will make DG more positive, and the reaction less likely to be spontaneous.

Answer 2

The best way to predict the entropy of a reaction is to consider the moles (i.e. coefficients) of each compound on either side of the reaction. If the sum of all the coefficients on the reactant side is greater than the sum of all the coefficients on the product side, the products are not favored and Delta S is Negative. That is, the reaction has more randomness on the left side. On the other hand if the sum of the coefficients are greater than the sum on the reactant sides, the reaction favors progression to the products and Delta S will be positive. That is, there is more randomness on the right side.