19. Chemical Thermodynamics

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?

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)

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:

The accompanying diagram shows how Δ𝐻 (red line) and 𝑇Δ𝑆 (blue line) change with temperature for a hypothetical reaction. Which of the following statements about this diagram is or are true?

b. The system is at equilibrium at 𝑇 = 300 K.

The conversion of natural gas, which is mostly methane, into products that contain two or more carbon atoms, such as ethane (C₂H₆), is a very important industrial chemical process. In principle, methane can be converted into ethane and hydrogen: 2 CH₄(g) → C₂H₆(g) + H₂(g) In practice, this reaction is carried out in the presence of oxygen: 2 CH₄(g) + 1/2 O₂(g) → C₂H₆(g) + H₂O(g)

c. Will the equilibrium constant for the second reaction increase, decrease, or stay the same if the temperature is increased to 500 °C?