Chemistry 2300
Assignment 2Professor: C. E. Loader
1.In a calorimeter 23.0 g of He(g) gas initially at 298 K is heated by passing a
current of 3.15 amps through a heater having a resistance of 4.75 ohms for 2.00
min. Calculate the final temperature ( = 12.5 J K–1 mol–1 of He) of the gas and
Cv
∆U gas if the calorimeter is
(a)at constant volume
(b)at constant pressure
2.3 moles of ideal gas ( = 12.5 J K–1 mol–1) is taken from an initial state (P =
Cv
1.5 atm, V = 9.3 L) to a final state (P = 1 atm, V = 6 L) by either of two reversible
paths: 1
(a)Path A a decrease in volume at constant pressure followed by a decrease in
pressure at constant volume.
(b)Path B a decrease in pressure at constant volume followed by a decrease in
volume at constant pressure.
For each path calculate ∆U, q and w for the gas.
3.2 moles of an ideal gas are placed in an melting ice bath. Calculate ∆U, Q and W
of the gas when it is slowly (reversibly) compressed to 1/3 its original volume.
How much ice is melted during this process? ∆Hfusion, ice = 6010 J mol–1.
4.During an expansion against a pressure of 1.00 atm, an ideal gas absorbs 209 J
as the volume is increased from 1 L to 10 L. Calculate the change in the internal
energy of the gas.
5.Calculate the final temperature when 100 g of ice at –20.8 ºC is added to 500 g of
liquid water initially at 83.9 ºC in an insulated container having negligible heat
capacity.
6.100 g of N2(g) is reversibly expanded from a pressure of 0.900 atm to 0.120 atm at
25 ºC. Calculate wgas, ∆Ugas, qgas.
7.Calculate ∆H for the processes:
(a)H2O(l, –10 ºC) H2O (s, –10 ºC)
(b)H2O(s, –10 ºC) H2O (g, –0 ºC)
∆H(fus, 0 º C) = 608 J mol–1 ∆H(vap, 100 º C) = 40.55 kJ mol–1
Cp (H2O, l) = 75.3 J K–1 mol–1 Cp (H2O, s) = 36.4 J K–1 mol–1
Cp (H2O, g) = 33.5 J K–1 mol–1
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