Textbook Question
Determine the sign of ΔSsys for each process. b. water freezing
625
views
Ch.18 - Free Energy and Thermodynamics
Chapter 18, Problem 87
Ethene (C2H4) can be halogenated by the reaction: C2H4(g) + X2(g) → C2H4X2(g) where X2 can be Cl2, Br2, or I2. Use the thermodynamic data given to calculate ΔH°, ΔS°, ΔG°, and Kp for the halogenation reaction by each of the three halogens at 25 °C. Which reaction is most spontaneous? Least spontaneous? What is the main factor responsible for the difference in the spontaneity of the three reactions? Does higher temperature make the reactions more spontaneous or less spontaneous?
Compound ΔH°f (kJ/mol) S° (J/mol·K)
C2H4Cl2(g) -129.7 308.0
C2H4Br2(g) +38.3 330.6
C2H4I2(g) +66.5 347.8
Verified step by step guidance1
Identify the thermodynamic data needed for the reactants and products: ΔH°f and S° for C2H4, Cl2, Br2, I2, C2H4Cl2, C2H4Br2, and C2H4I2.
Calculate ΔH° for each reaction using the formula: ΔH° = ΣΔH°f(products) - ΣΔH°f(reactants).
Calculate ΔS° for each reaction using the formula: ΔS° = ΣS°(products) - ΣS°(reactants).
Calculate ΔG° for each reaction using the formula: ΔG° = ΔH° - TΔS°, where T is the temperature in Kelvin (298 K for 25 °C).
Determine Kp for each reaction using the relationship: ΔG° = -RTlnKp, where R is the gas constant (8.314 J/mol·K). Compare ΔG° values to assess spontaneity and discuss the effect of temperature on spontaneity.
Related Practice
Open Question
Our atmosphere is composed primarily of nitrogen and oxygen, which coexist at 25 °C without reacting to any significant extent. However, the two gases can react to form nitrogen monoxide according to the reaction: N2(g) + O2(g) → 2 NO(g). a. Calculate ΔG° and Kp for this reaction at 298 K. Is the reaction spontaneous? b. Estimate ΔG° at 2000 K. Does the reaction become more spontaneous as temperature increases?
Textbook Question
Nitrogen dioxide, a pollutant in the atmosphere, can combine with water to form nitric acid. One of the possible reactions is shown here. Calculate ΔG° and Kp for this reaction at 25 °C and comment on the spontaneity of the reaction. 3 NO2(g) + H2O(l)→ 2 HNO3(aq) + NO(g)
1274
views
Open Question
H2 reacts with the halogens (X2) according to the reaction: H2(g) + X2(g) → 2 HX(g) where X2 can be Cl2, Br2, or I2. Use the thermodynamic data in Appendix IIB to calculate ΔH°, ΔS°, ΔG°, and Kp for the reaction between hydrogen and each of the three halogens. Which reaction is most spontaneous? Least spontaneous? What is the main factor responsible for the difference in the spontaneity of the three reactions? Does higher temperature make the reactions more spontaneous or less spontaneous?
Textbook Question
Consider this reaction occurring at 298 K: N2O(g) + NO2(g) ⇌ 3 NO(g) a. Show that the reaction is not spontaneous under standard conditions by calculating ΔG°rxn.
1400
views
Textbook Question
Consider this reaction occurring at 298 K: N2O(g) + NO2(g) ⇌ 3 NO(g) b. If a reaction mixture contains only N2O and NO2 at partial pressures of 1.0 atm each, the reaction will be spontaneous until some NO forms in the mixture. What maximum partial pressure of NO builds up before the reaction ceases to be spontaneous?
1806
views