Chemistry help, please?

Question

Consider the reaction below.

2 POCl3(g) ---->2 PCl3(g) + O2(g)

(a) Calculate G° for this reaction. The Gf° values for POCl3(g) and PCl3(g) are -502 kJ/mol and -270. kJ/mol, respectively.
(b) Is this reaction spontaneous under standard conditions at 298 K?
(c) The value of S° for this reaction is 179 J/K. At what temperatures is this reaction spontaneous at standard conditions? Assume that H° and S° do not depend on temperature.

Okay, so i already got A and B--

a is 464
and b is no

however, i don't understand why b is no.

and c, i don't understand because how can you solve without the enthalpy value??

can someone please help me with B and C?

how do i find delta H?
my book doesn't have such specific values and i can't find it on the internet

Answer 1

B is "no" because the standard free energy change is greater than zero. If Delta G has a negative value, the reaction is spontaneous. If Delta G is greater than zero, the reaction is not spontaneous.

For C, you are going to have to calculate Delta H° for the reaction. You do this the same way you did for Delta Gzero, but using enthalpies of formation.

Once you get Delta H° for the reaction, use the equation:

DG=DH-TDS (D=delta).

Set DG equal to zero, use your values for DH and DS and solve for T. THat will be the temperature where the reaction will become spontaneous. If the value of T is greater than 298, then at any temperature above that, the reaction will be spontaneous. If T is less than 298, the reaction will be spontaneous at all temperatures below that.