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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 25Â°C?

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

2. Some standard entropies (at 25Â°C in J/mol K) are given:
Ca2+(aq) -55.2, F-(aq) -9.6, CaF2(s) +68.87. &#916;SÂ° for the reaction CaF2(s) &#61614; Ca2+(aq) + 2F-(aq) at 25Â°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 SÂ°

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

determine the &#916;SÂ° (in J/mol -K) for the reaction:

C2H2 (g) + H2 (g) &#61614; 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 25Â°C.
Substance &#916;GÂ°f (kJ/mol) SÂ° (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 &#916;HÂ° (in kJ) for the reaction described below? Assume the reaction is performed at 25Â°C.

C2H2 (g) + 2H2 (g) &#61614; C2H6 (g)

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