[raffster2]

1. "Predict the sign of the molar Gibbs free energy for the process H2O(s) >> H2O(l) at 1 atm for the following three temperatures: 1C, 0C, -1C"

Okay, I calculated the deltaH and deltaS and got -285.85 kJ/mol and 69.91 J/mol*K. Since G=H-TS, then wouldn't the sign be negative for all three temperatures?

2. Which of the following statements is true regarding the following reaction: Cl2(g) >> 2Cl(g)
A. Reaction os spontaneous at high temps
B. Reaction is spontaneous at low temps
C. Reaction is not spontaneous at any temps
D. Reaction is spontaneous at all temps

I know that it's either A or C, since Cl2 is the most stable form of chlorine gas, but would it become spontaneous at high temperatures?

3. Calculate the change in internal energy when 2.5 kJ of energy is transferred as heat to 1.5 mol BF3 at 298 K and 1 atm at constant volume.

Since it's at constant volume, w=0, so the internal energy change would just be +2.5kJ, right? Just want to make sure because this seems too simple.


Thanks a lot!

[Donaldson Tan]

1. "Predict the sign of the molar Gibbs free energy for the process H2O(s) >> H2O(l) at 1 atm for the following three temperatures: 1C, 0C, -1C"

Okay, I calculated the deltaH and deltaS and got -285.85 kJ/mol and 69.91 J/mol*K. Since G=H-TS, then wouldn't the sign be negative for all three temperatures?

Are you sure dH and dS would be these values at temperatures -1C, 0C and 1C? I prefer a simpler approach. I know the freezing point of water at 1atm is 0C. During phase change, water and ice would be at equilibrium with each other. Hence dG_1atm,0C = 0 kJ/mol. Negative dG suggests that the corresponding reaction would be spontaneous at the specified temperature and pressure. Ice melts above its freezing point, hence dG_1atm,1C < 0 and dG_1atm,-1C > 0

2. Which of the following statements is true regarding the following reaction: Cl2(g) >> 2Cl(g)
A. Reaction is spontaneous at high temps
B. Reaction is spontaneous at low temps
C. Reaction is not spontaneous at any temps
D. Reaction is spontaneous at all temps

I know that it's either A or C, since Cl2 is the most stable form of chlorine gas, but would it become spontaneous at high temperatures?

The answer is A. This reaction takes place at high temperature or in the presence of UV.

3. Calculate the change in internal energy when 2.5 kJ of energy is transferred as heat to 1.5 mol BF3 at 298 K and 1 atm at constant volume.

Since it's at constant volume, w=0, so the internal energy change would just be +2.5kJ, right? Just want to make sure because this seems too simple.

You are right about Q3.