Textbook Question
A reaction has an equilibrium constant of 8.5⨉103 at 298 K. At 755 K, the equilibrium constant is 0.65. Find ΔH°rxn for the reaction.
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Ch.18 - Free Energy and Thermodynamics
Chapter 18, Problem 85
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?
Verified step by step guidance1
<insert step 1: Identify the standard Gibbs free energy change (ΔG°) equation: ΔG° = ΔH° - TΔS°. You will need the standard enthalpy change (ΔH°) and the standard entropy change (ΔS°) for the reaction.>
<insert step 2: Look up or calculate the standard enthalpy change (ΔH°) and the standard entropy change (ΔS°) for the reaction using standard thermodynamic tables.>
<insert step 3: Calculate ΔG° at 298 K using the equation from step 1.>
<insert step 4: Use the relationship between ΔG° and the equilibrium constant (Kp) at a given temperature: ΔG° = -RT ln(Kp), where R is the gas constant and T is the temperature in Kelvin. Solve for Kp.>
<insert step 5: To estimate ΔG° at 2000 K, use the same equation from step 1, assuming ΔH° and ΔS° are approximately constant over the temperature range. Compare the ΔG° values at 298 K and 2000 K to determine if the reaction becomes more spontaneous at higher temperatures.>
Related Practice
Textbook Question
Determine the sign of ΔSsys for each process. a. water boiling
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Textbook Question
Determine the sign of ΔSsys for each process. b. water freezing
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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)
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Open Question
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
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?