7. Energy, Rate and Equilibrium

What are the signs of ∆H, ∆S and ∆G for the spontaneous conversion of a solid into gas?

Consider the combustion of butane gas and predict the signs of ΔS, ΔH and ∆G.

C₄H₁₀(g) + 13/2 O₂(g) ⟶ 4 CO₂(g) + 5 H₂O(g)      

A particular reaction has ΔG = –350 kJ and ΔS = –350 J/K at 24°C. How much heat will be released/absorbed?

For a reaction in which ΔH = 125 kJ and ΔS = 325 J/K, determine the temperature in Celsius above which the reaction is spontaneous.

The change of state from liquid H₂O to gaseous H₂O has ∆H = +9.72 kcal/mol(+40.7 kJ/mol) and ∆S = -26.1 cal/(mol • K) [-109 J/(mol •K)].

a. Is the change from liquid to gaseous H2O favored or unfavored by ∆H? By ∆S?

The change of state from liquid H₂O to gaseous H₂O has ∆H = +9.72 kcal/mol(+40.7 kJ/mol) and ∆S = -26.1 cal/(mol • K) [-109 J/(mol •K)].

b. What are the values of ∆H and ∆S (in kcal/mol and kJ/mol) for the change from gaseous to liquid H2O?

Two curves are shown in the following energy diagram:

b. Which curve represents the spontaneous reaction, and which the nonspontaneous?

The following diagram portrays a reaction of the type A(s) → B(g) + C(g), where the different-colored spheres represent different molecular structures. Assume that the reaction has ∆H = +9.1 kcal/mol (+38.1 kJ/mol).

b. Is the reaction likely to be spontaneous at all temperatures, nonspontaneous at all temperatures, or spontaneous at some but nonspontaneous at others?

The following diagram portrays a reaction of the type A(s) → B(g) + C(g), where the different-colored spheres represent different molecular structures. Assume that the reaction has ∆H = +9.1 kcal/mol (+38.1 kJ/mol).

a. What is the sign of ∆S for the reaction?

What two factors affect the spontaneity of a reaction?

What is the difference between an exothermic reaction and an exergonic reaction?

Under what conditions might a reaction be endothermic but exergonic? Explain.

For the reaction 2 Hg(l) + O₂(g) → 2 HgO(s), ∆H = –43 kcal/mol (–180 kJ/mol).

b. Under what conditions would you expect this process to be spontaneous?

The reaction between hydrogen gas and carbon to produce the gas known as ethylene is:

2 H₂(g) + 2 C(s) → H₂C=CH₂(g), ∆G = +16.3 kcal/mol (+68 kJ/mol) 25 °C.

a. Is this reaction spontaneous at 25 °C?

You calculate the value of ΔG for a chemical reaction and get a positive value. Which would be the most accurate way to interpret this result?