Which of the following reactions are spontaneous (favorable)?

A] 2Mg(s) + O2(g) -> 2MgO(s) Delta G = -1137 kJ/mol ..
B] NH3(g) + HCl(g) -> NH4Cl(s) Delta G = -91.1 kJ/mol ...
C] AgCl(s) -> Ag+(aq) + Cl-(aq) Delta G = 55.6 kJ/mol ..
D] 2H2(g) + O2(g) -> 2H2O(g) Delta G = 456 kJ/mol
E] C(s) + H2O(l) -> CO(g) + H2(g) Delta G = 90.8 kJ/mol
F] CH4(g) + 2O2 -> CO2(g) + 2H2O(l) Delta G = -820 kJ/mol

I said that reaction A, B, and F were spontaneous because my book said spontaneity occurs when Delta G < 0 ... but theres also an example of a dissociation equation being spontaneous.. does that mean that reaction C is also spontaneous?

No. dG for C is >0; therefore, it is not spontaneous. What dissociation equation is listed as spontaneous.

Hello Dr. Bob,

This was the equation: 2N2O(g) ---> 2N2(g) + O2

I'm not sure I would call that a dissociation reaction. When I think of a dissociation reaction the AgCl ==>? Ag^+ + Cl^- is one; another one is CH3COOH ==> H^+ +CH3COO^-, NaCl + H2O => Na^+(aq) + Cl^-(aq), etc.

What you have written I call a reaction( specifically a decomposition) and not a dissociation. We would guess, by the way, that the decomposition of NO2 to N2 and O2 is spontaneous because the reverse reaction is NOT spontaneous. If it were, there wouldn't be much O2 around in the atmosphere for us to breathe.

Ohhh.. my mistake I understand now. thanks!

Which of the following reactions are spontaneous (favorable)?

A. DHAP ---> glyceraldehyde - 3 - phosphate ΔG=3.8 kJ/mol
B. C2H4+H2 ----> C2H6 ΔG=-150.97kJ/mol
C. C4H4O5 ---> C4H2O4+H2O ΔG=3.1 kJ/mol
D. L-malata + NAD + ---> oxalocacetate + NADH+H^+ ΔG=29.7 kJ/mol
E. glutamate + NAD^+ H2O ---> NH4^+ a-ketoglutarate+NADH+H^+ ΔG=3.7 kcal/mol
F. C6H13O9P+ATP ---> C6H14O12P2+ADP ΔG=-14.2 kJ/mol

You are correct that for a reaction to be spontaneous, the standard Gibbs free energy change (ΔG) must be negative (ΔG < 0).

Let's analyze the given reactions:

A] 2Mg(s) + O2(g) -> 2MgO(s) ΔG = -1137 kJ/mol

Since ΔG is negative, this reaction is spontaneous.

B] NH3(g) + HCl(g) -> NH4Cl(s) ΔG = -91.1 kJ/mol

Again, ΔG is negative, so this reaction is also spontaneous.

C] AgCl(s) -> Ag+(aq) + Cl-(aq) ΔG = 55.6 kJ/mol

In this case, ΔG is positive (greater than 0), which means the reaction is non-spontaneous under standard conditions.

D] 2H2(g) + O2(g) -> 2H2O(g) ΔG = 456 kJ/mol

ΔG is positive, so this reaction is non-spontaneous.

E] C(s) + H2O(l) -> CO(g) + H2(g) ΔG = 90.8 kJ/mol

Again, ΔG is positive, indicating a non-spontaneous reaction.

F] CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l) ΔG = -820 kJ/mol

ΔG is negative, confirming that this reaction is spontaneous.

To summarize, reactions A, B, and F are spontaneous because their ΔG values are negative. On the other hand, reactions C, D, and E are non-spontaneous due to their positive ΔG values.

Regarding reaction C (AgCl dissociation), while ΔG is positive, it represents the standard free energy change under standard conditions. However, in certain situations, such as adding excess Cl- or increasing the temperature, the equilibrium can shift, making the reaction spontaneous.

its D, E,A