09-214 Physical Chemistry Name___(Corrected)_________

Quiz 1 January 26, 2000

Closed book. No equations in calculators. Show all work. Watch correct units, signs and significant figures.

1 L-atm = 101.3 joules

A breath of air has a volume of 0.50 L when inhaled and comes to thermal equilibrium with the body at 37^oC while the pressure remains constant at 1 atm. Assume air is an ideal gas for which . For air is 29 J/K-mol and is independent of T over a wide temperature range. R = 8.3 kJ/K mole = 0.082 L atm/K mole.

1. Calculate the increase in enthalpy of the air in the lungs if the initial temperature is -13^oC (9^oF).

n = PV/RT = 1 atm * 0.5 L/(0.082 L-atm /K mol)(260 K) = 0.023 mol

H = nC_P(T₂-T₁) = 0.023 mol * 29 J/K-mol * ( 50 K ) = 33.4 J

2. At a breathing rate of 12 breaths per minute, how much heat is lost in this fashion in 1 hour?

(33.4 J/breath)(12 breaths/min)(60 min/hr)(24 hr/day) = 200000 J/day = 289 kJ/day

3. How much work is done in one breath by the lungs exhaling 0.50 L against an opposing force of 1 atm?

w = -P_exV = -(1 atm)(.50 L) = -.50 L-atm (--> -.50 L-atm*101.3 J/L-atm = -50 J)

4. How much work would be done by the lungs in one breath if the incoming air were at 37^oC instead of -12^o?

same as above