Question

1. A chemical reaction at 304 K has an enthalpy change (delta-H) of -73.9 kJ/mol and an entropy change (delta-S) of 161.6 kJ/mol. What is its Gibbs energy change, delta-G, in kJ/mol? Give the answer to one decimal place.

2.Use the thermodynamic data in your textbook to determine the temperature below which the following reaction is spontaneous. (Give the temperature in K, to the nearest degree.)

2SO2 (g) + O2 (g) -- 2SO3 (g)

3.What is the delta-G for the dissolution of Na2CO3 in water?

Give the answer in kJ/mol, using the data in the book.

Answer 1

H = -73.9 kJ/mol = -73.9 x 10³ J/mol

S = 161.6 J/mol.K =

T = 304 K

G = -73.9 x 10³ - (161.6)(304) = -73900-18726.4 = -92626 J/mol = 92.6 kJ/mol

part 2

2 SO2(g) + O2 2SO3

standard thermodynamic values are

H = -197.8 kJ

S = -188 J

for a reaction to be spontaneous , gibbs free energy must be negative

when G < 0

T > - 197.8 x 1000 / 188 = 1052 K

for this reaction to be spontaneous, T must be greater than 1052 K

part 3