Question

Consider the following reaction: 2A(g) + B(g) --> 2 C(s). ∆H = + 430 kcal/mol. Since this reaction is __, and ∆S is __ (because the number of gas molecules decreases), then ∆G must be__, and the reaction is NOT__ ?

Answer 1

• endothermic
• negative
• positive
• spontaneous

Explanation:

1. Reaction is endothermic because `Δ"H"` is positive.
2. `Δ"S"` is negative because gases (`"A"` and `"B"`) are reacting to form solid (`"C"`). Randomness is decreased
3. In this reaction `Δ"H"` is positive and `Δ"S"` is negative therefore `Δ"G"` must be positive, because it’s given by the equation `Δ"G" = Δ"H" - "T"Δ"S"`
4. As `"ΔG"` is positive, reaction is non-spontaneous

`Δ"G" < 0` - Reaction is spontaneous
`Δ"G" > 0` - Reaction is non-spontaneous
`Δ"G" = 0` - Reaction is at equilibrium