19. Chemical Thermodynamics

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)

If ∆G is small and positive which of the following statements is true?

Nitrogen gas combines with fluorine gas to form nitrogen trifluoride according to the reaction below at 25^oC:

N₂ (g)  +  3 F₂ (g)  →  2 NF₃ (g)               ΔH^o = -249.0 kJ                       ΔS^o = -278 J/K

Calculate ΔG^o and state if the reaction favors reactants or products at standard conditions.

3 C (s, graphite) + 4 H₂ (g) → C₃H₈ (g)

The chemical reaction 2 NO₂Br (g) → 2 NO₂ (g) + Br₂ (g) has a K_eq = 4.50 × 10⁵.

Does the reaction increase the entropy of the Universe? Explain.

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

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?

a) If a mixture of reactants and products is created and left to equilibrate, the equilibrium mixture will contain more reactant than product.

b) If a mixture of reactants and products is created, we cannot say anything about its composition at equilibrium but we can say it will reach equilibrium very rapidly.

c) The reaction will not occur under any circumstances.

d) If a mixture of reactants and products is created and left to equilibrate, the equilibrium mixture will contain more product than reactant.

Reactions in which there is a negative change in free energy (–ΔG) are: