Short Answer:
1) (6 pnts) Explain (in english, not just equations) why the heat capacity at constant pressure is generally greater than the heat capacity at constant volume for a gas.
2) (6 pnts) Consider a system in an adiabatic, rigid container. Will the internal energy of the system increase, decrease or stay the same if an exothermic reaction occurs inside the container? Why?
3) (18 pnts)
(a)Is the work done by allowing an ideal gas to expand into a vacuum positive, negative or
zero? Why?
(b) In part a, if the system is adiabatic, will the temperature of the gas increase, decrease or stay the same upon expansion (assuming it is ideal). Why?
(c) What would have been your answer to the last problem if the Joule Thompson coefficient of the gas had been positive (not an ideal gas)? Explain.
Short Numerical Answer
4) (15 pnts) If we were to isothermally compress an ideal gas from 8.0 liters to 4.0 liters resulting in a final pressure of 3 atm, what was the original pressure?
5) (15 pnts) If one wanted to run a reaction between molecular hydrogen and molecular oxygen in a 10 liter flask to form one mole of water, what mole fractions and partial pressures of the two reacting gases would be required? (Assume all reactants and products are ideal gases at 25 C).
6) (15 pnts) 2 moles of an ideal gas is expanded isothermally from 1 liter to 2 liters at 25 C against an external pressure of 1 atm. Calculate w, q, the change in internal energy and the change in enthalpy for this process.
Applying the concepts and calculations
7) (25 pnts) It is usually suggested that one carry about four liters of water per day per person when hiking in the desert under moderate weather conditions. How many degrees can four liters of water cool a 65 kg person if it is consumed and then evaporates due to respiration and sweat? Assume that people are made entirely of water (a pretty good approximation) and that the heat capacity at constant pressure of a person is the same as that of water ( 75.3 J/(K mol) ). The molar enthalpy of fusion for water is 6.00 kJ and the molar enthalpy of vaporization is 40.66 kJ. The density of water is about 1.00 kg/liter at normal temperatures. The molecular weight of water is 18.