Home Chapter 19: Chemical Thermodynamics Homework 5

# Homework 5

This activity contains 12 questions.

Calculate G° for the reaction below at 25°C.

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

SubstanceHf°(kJ/mol)S°(J/mol·K)
SO2(g)-297249
O2(g)0205
SO3(g)-395256

 -149 kJ -196 kJ -39.0 kJ -253 kJ -200 kJ

## Calculate G° in kJ for the following reaction at 25°C if the value of Keq is 6.1 x 10-58.3O2(g) --> 2O3(g)

 -1.51 x 10-54 3.22 27.4 326 -326

## For each of the following pairs, choose the substance with the higher entropy per mole at a given temperature: (i) O2(g) at 5 atm or O2(g) at 0.5 atm, (ii) Br2(l) or Br2(g)

 (i) O2(g) at 0.5 atm, (ii) Br2(g) (i) O2(g) at 0.5 atm, (ii) Br2(l) (i) O2(g) at 5 atm, (ii) Br2(l) (i) O2(g) at 5 atm, (ii) Br2(g)

## For which of the following processes will S° system be the most positive?

 2SO2(g) + O2(g) --> 2SO3(g) 4Fe(s) + 3O2(g) --> 2Fe2O3(s) C2H2(g) + H2(g) --> C2H4(g) Hg(l) --> Hg(s) 2NH3(g) --> N2(g) + 3H2(g)

## For which one of the following substances is Gf° zero?

 O(g) H2O(l) N2(g) Br2(s)

Given the following standard molar entropies, calculate S in J/K° for the reaction

 C(s) + O2(g) --> CO2(g) S° J/mol·K 5.74 205.0 213.6

 424.3 2.9 -2.9 -424.3 none of these

## The molar heat of vaporization for ethanol is 37.4 kJ/mol. If the boiling point of ethanol is 78.0°C, calculate S in J/K for the vaporization of 0.500 mol ethanol.

 240 0.24 107 0.0533 53.3

## Use data from Appendix C to calculate Kp at 298 K for the reactionH2(g) + I2(g) 2HI(g).

 1.47 x 103 8.70 x 102 0.350 1.01 1.15 x 10-3

Use the following data to calculate G° in kJ at 155°C for the reaction

 2O3(g) --> 3O2(g) Hf° kJ/mol 142.7 0 S° J/mol·K 238.8 205.0

 -344.2 -285.4 -128.2 137.4 none of these

Which of the following conditions are true for a reaction that is spontaneous at low temperatures and becomes nonspontaneous at a higher temperature? (Assume that H and S do not change with temperature.)

 H < 0, S > 0 H > 0, S > 0 H > 0, S < 0 No conditions allow for such a result. H < 0, S < 0

## Which one of the following has the greatest entropy?

 They all have the same entropy. HCl(g) HCl(l) HCl(s)

## Without consulting a table of values, predict the relative trend of entropy per mole for molecular oxygen, ozone, and monatomic oxygen gases under identical conditions.

 O2 < O < O3 O2 < O3 < O O2 < O3 < O O < O2 < O3 O3 < O2 < O