COLLEGE OF SAINT MARY FALL 2008 PHYSICAL CHEMISTRY INSTRUCTOR: DR. PETER ILICH

HOMEWORK # 02

HEAT EXCHANGE

A mountain saga:

(1) A mountain climber runs into a sudden, cold rainstorm (t _rain = 6 °C) and unable to find a shelter, becomes completely soaked. The rain stops as fast as it started and a steady wind arises that dries her clothes completely within 40 minutes. Assuming , (a) Calculate how much heat she has lost within these 40 minutes. (b) Calculate how much her body temperature has dropped from 36.6 °C. (Assume that the climber and the clothes weigh 65.0 kg, that she (her clothes, actually) absorbed 1.2 kg of rainwater, and, for the lack of specific data, that the heat capacity of her body plus the clothes is equivalent to that of water.)

EXERCISE & WEIGHT

Wish it were so simple:

(2) After 40 minutes of steady pace running (~ 32 kJ/min; http://www.biofizyka.slam.katowice.pl/lab/lab5.prn.pdf) a jogger is offered these three meals: (A) burger king with cheese 1593 kJ [http://www.nal.usda.gov/fnic/foodcomp/cgi-bin/list_nut_edit.pl], (B) a bowl (250 g) of cooked lentils [find the energy] or (C) a Snickers (MARATHON Protein Performance) bar, 1346 kJ. Given that she chooses (C) and assuming that she burned only body fat (wishful thinking!) [3500 calories per pound of fat tissue, http://www.weightlossforall.com/calories-per-pound.htm], what is her gross energy balance ?

ENTROPY CHANGE

If only it were in the numbers:

(3) Predict the expected entropy change (positive or negative) without consulting thermodynamics data for the following processes:

Entropy change: positive OR negative

(a) Br₂(liq) → Br₂(gas) _____________

(b) Egg (raw) → egg (hard-boiled) _____________

(d) H₂O(salty) → H₂O(de-salinated) _____________

(e) C(soot) → C(diamond) _____________

(f) N₂(g) + 3 H₂(g) → 2 NH₃(g) (Haber-Bosch process) _____________

(g) CH₂OHCHOHCHOHCHOHCHOHCHO(glucose,s) + 6 O₂(g) → 6 CO₂(g) + 6 H₂O(l) _____________

(h) song (live performance) → song (recorded on CD) _____________