Leader: Ryan Gale
Course: Chem 178
Instructor: Burnett
Supplemental Instruction
Date: 4/10/13
Iowa State University
1.) Make a diagram with Gibbs Free Energy on the y-axis and reaction progress on the x-axis.
The reaction being analyzed is exothermic and has a decrease in entropy of reaction. How
can you draw a curve and qualitatively see if the system is spontaneous with temperature?
∆𝐺 = ∆𝐻 − 𝑇∆𝑆
Thermodynamics Quiz
Review
2.) For a certain chemical reaction, it is exothermic and decreasing in entropy. What will the
sign of Gibbs Free Energy be for this? What about endothermic and increasing entropy?
Be sure to specify ranges of T if needed.
3.) The following diagram has TΔS on the y-axis and ΔH on the x-axis. What is the
significance of the x-intercept = 400 K. At what temperature range is this reaction
spontaneous?
Supplemental Instruction
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4.) Acetylene gas, C2H2(g) is used in wielding, and combusts with oxygen in the air.
a. Write the balanced chemical equation for this reaction.
b. How much heat is produced when burning 1 mol of acetylene under standard
conditions?
ΔH°C2H2(g) = 226.77 kJ/mol, ΔH°CO2(g) = -393.5 kJ/mol, ΔH°H2O(l) = -285.83 kJ/mol
ΔS°C2H2(g) = 200.8 J/molK, ΔS°O2(g) = 205.0 J/molK, ΔS°CO2(g) = 213.6 J/molK,
ΔS°H2O(l) = 69.91 J/molK
c. What is the maximum amount of useful work that can be accomplished under
standard conditions by this reaction? (Hint: What is Gibbs Free Energy in reality?)
5.) Calculate the equilibrium constant at 298 K for the following reaction ΔG = ΔG°+RTln(Q):
2HBr(g) + Cl2(g) → 2HCl(g) + Br2(g)
HHBr(g) = -36.23 kJ/mol HHCl(g) = -92.30 kJ/mol
SHBr(g) = 198.49 J/molK SCl2(g) = 222.96 J/molK SHCl(g) = 186.69 J/molK
SBr2(g) = 245.3 J/molK