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Gas-phase absolute entropy

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1. Which molecule below should have the highest gas-phase absolute entropy at 25°C?

a. CH4
b. H2
c. C2H6
d. C2H4
e. C2H2

2. Some standard entropies (at 25°C in J/mol K) are given:
Ca2+(aq) -55.2, F-(aq) -9.6, CaF2(s) +68.87. ΔS° for the reaction CaF2(s)  Ca2+(aq) + 2F-(aq) at 25°C in J/K is __________.

a. -5.5
b. -133.7
c. +133.7
d. -143.3
e. +143.3

3. Given the following table of thermodynamic data,
substance S°

C2H2 (g) 200.8 J/mol - K
C2H4 (g) 219.4
C2H6 (g) 229.5
H2 (g) 130.58

determine the ΔS° (in J/mol -K) for the reaction:

C2H2 (g) + H2 (g)  C2H4 (g)

a. -232.46
b. +111.98
c. +101.88
d. -101.88
e. -111.98

4. The standard free energy of formation of __________ is zero.

a. O (g)
b. H2O (l)
c. N2 (g) and O (g)
d. N2 (g)
e. Br2 (s)

5. Consider the following table of thermodynamic data. All values are tabulated for 25°C.
Substance ΔG°f (kJ/mol) S° (J/mol ? K)

C2H2 (g) 209 201
C2H4 (g) 68 219
C2H6 (g) -33 230
H2 (g) 0 131
H2O (g) -229 189
C2H5OH (l) -175 161

What is the value of ΔH° (in kJ) for the reaction described below? Assume the reaction is performed at 25°C.

C2H2 (g) + 2H2 (g)  C2H6 (g)

a. -173
b. -248
c. -311
d. 149
e. 236

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Solution Summary

Multiple choice questions and corresponding answers to general chemistry inquiries, regarding gas-phase entropies, thermodynamic data, and energy formation.

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Calculate delta G; temperature; pressure

Kp is 1.0x10-3 atm-1/2 at 2000K and delta S at standard temperature and pressure = 87.864 J/K mole (delta Cp = 0) for the reaction
CO2(g) yielding CO(g) + 1/2 O2(g) (this reaction is reversible)

(a) Calculate delta G at 2000K,
(b) Calculate delta G at standard temperature and pressure at 298K, and
(c) Calculate the degree of dissociation of CO2 if the equilibrium mixture is brought to 2000K and 2 atm total pressure (assume enthalpy and entropy are temperature independent)

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