Transcript Welcome to Chem 1A CLAS with Eric Engel

Thermodynamics (Ch 10)
1. One mole of helium in a volume of 1.0 L at
5.0 atm pressure is allowed to expand isothermally
into a volume of 2.0 L. Calculate the work done if:
a. the gas expands into an evacuated container
b. the gas expands, in one step, against a constant
external pressure of 2.5 atm
c. the gas expands reversibly
Thermodynamics (Ch 10)
2. For the following, state whether there will be
an increase or decrease in entropy.
a. freezing water
b. dissolving calcium chloride
c. formation of NH3(g)
Thermodynamics (Ch 10)
3. Circle the one with the greatest entropy.
a. 1 mol of He at STP or
1 mol of He at 50 ˚C and 1 atm
b. 1 mol of N2 at STP or
1 mol of SF6 at STP
c. 1 mol of Ne at 25 ˚C, 1 atm or
1 mol of Ne at 25 ˚C, 0.01 atm
Thermodynamics (Ch 10)
4. A sample of ice weighing 36.0 g, initially at
-20.0 ˚C, is heated to 150. ˚C at a constant
pressure of 1.00 atm. Calculate q, w, ΔE, ΔH
and ΔS for this process.
(Cp(ice) = 37.5 J/Kmol, Cp(liquid) = 75.3 J/Kmol
Cp(gas) = 36.4 J/K mol,
ΔHfusion = 6.01 kJ/mol, ΔHvaporization= 40.7 kJ/mol)
Thermodynamics (Ch 10)
5. Calculate the change in entropy that occurs
when 3.00 mol of liquid water at 0.0 ˚C is
mixed with 1.00 mol of water at 90. ˚C in a
perfectly insulated container.
(Cp = 75.3 J/K mol)
Thermodynamics (Ch 10)
6. Consider the freezing of water.
a. Use the following to calculate ΔH˚ and ΔS˚ for this
process.
ΔH˚f
S˚
H2O (l)
-286 kJ/mol
70 J/K mol
H2O (s)
-292 kJ/mol
48 J/K mol
b. Calculate a value for ΔG˚ for this process at three
different temperatures: 25 ˚C, -15 ˚C and 0 ˚C.
Thermodynamics (Ch 10)
ΔH
ΔS
Spontaneous?
-
+
Always
-
-
At low T only
+
+
At high T only
+
-
Never
Thermodynamics (Ch 10)
7. The melting point of tungsten is 3680 K.
The enthalpy of fusion is 35.2 kJ/mol.
What is the entropy of fusion for tungsten?
Thermodynamics (Ch 10)
8. Consider the reaction
2 POCl3(g)  2 PCl3(g) + O2(g)
a. Calculate ΔG˚ for this reaction, given that the ΔG˚f
values for POCl3(g) and PCl3(g) are -502 kJ/mol and
-270 kJ/mol, respectively.
b. Is the reaction spontaneous under standard conditions
at 298 K?
c. The value of ΔS˚ for the reaction is 179 J/K mol. At
what temperatures is this reaction spontaneous?
Thermodynamics (Ch 10)
9. Given the following reaction at 800 K:
N2(g) + 3 F2(g)  2 NF3(g)
a. An equilibrium mixture contains the following
partial pressures: 0.021 atm N2, 0.063 atm F2
and 0.48 atm NF3. Calculate ΔG˚ for the
reaction at 800 K.
b. What is ΔG if the pressures of the gases are 0.1
atm F2, 0.1 atm N2 and 5 atm NF3 at 800 K.
Thermodynamics (Ch 10)
10. The equilibrium constant for a certain
reaction decreases from 8.84 to 0.0325 when the
temperature increases from 25 to 75 ˚C. Is the
reaction endo- or exothermic? Calculate ΔH˚ for
the reaction.