1. (20%)
One mole of N2 gas is contained at 273 K and a pressure of 1 atrn. The addition
of 3000 J of heat to the gas at constant pressure causes 832 J of work to be done
during the expansion.
Calculate:
(1) the final state of the gas,
(2) the values of AU and A H for the change of state,
(3) the values of c, and c, for NZ.Assume that nitrogen behaves as an ideal gas,
and that the above change of state is conducted reversibly.
(4) If the heat supplied was 1500 J, what was the final state if the expansion was
also conducted reversibly at constant pressure?
(5) How much work was it done during the expansion?
2.
(20%)
Calculate the change in enthalpy and the change in entropy when one mole of Sic
is heated from 25°C to 1000°C. The constant pressure molar heat capacity of Sic
varies with temperature as:
T - 4.92 x 106 T2 + 8.20 x lo8 T' (J1mole.K)
c, = 50.79 + 1.97 x
3. (20%)
Determine the maximum pressure of water vapor in wet hydrogen at 1 atm
pressure in which chromium can be heated without oxidation occurring at 1500 K. Is
the oxidation of Cr by water vapor exothermic or endothermic?
4. (20%)
n moles of an ideal gas A and (1-n) moles of an ideal gas B, each at 1 atm pressure,
are mixed at total constant pressure. What ratio of A to B in the mixture maximizes
the decrease in the Gibbs free energy of the system? If the decrease in the Gibbs free
energy is A G ~to, what value must the pressure be increased in order to increase the
Gibbs free energy of the gas mixture by % A G ~?
5. (20%)
A1203,which melts at 2324 K, and Cr203, which melts at 2538 K, form complete
ranges of solid and liquid solutions. The molar heat of melting of A1203 is 107,500 J,
and assuming that ASom,cao3= aS0m,A1203
and that the solid and liquid solutions in
the system A1203-Cr203 behave ideally. Calculate a few points on solidus and
liquidus lines (compositions versus temperatures) and draw the phase diagram of
A1203- Cr203 system.
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