Question

28.Consider a reaction for which ?H =-30.91 kJ/mol, ?S =-93.2J/K-mol. Which of the following statements is true?

A)The reaction is spontaneous at all temperatures

B)The reaction is spontaneous at low temperatures?332 K

C)The reaction is spontaneous at high temperatures?332 K

D)The reaction is spontaneous at high temperatures?3.02 K

E)The reaction is never spontaneous

13.Calculate the pH of a buffer solution that is 0.250 M in HClO and 0.170 M KClO. The acid ionization constant for HClO at 298 K is 2.9×10-8

A)7.37

B)7.71

C)1.77

D) 6.98

E) 7.54

Answer 1

Ans 28

Enthalpy ?H = - 30.91 kJ/mol

Entropy ?S = - 93.2 J/mol·K

?H >> ?S

Gibbs free energy

?G = ?H - T?S

?H < 0

?S < 0

For given conditions, ?G < 0

The reaction becomes spontaneous at

T = ?H/?S = (-30.91*1000 J/mol) / (-93.2 J/mol·K)

T = 331.65 K

The reaction is spontaneous at low temperatures

Option B is the correct answer

The reaction is spontaneous at all temperatures if ?H < 0, ?S > 0 and ?G < 0

The reaction is spontaneous at high temperatures if ?H > 0, ?S > 0 and ?G < 0

The reaction is never spontaneous if ?G > 0