5. Assume you have a 45°C 100g block of gold (cp=0.129J/g°C) and a 150°C , 150g block of silver (cp=0.240J/g°C)(1). You place these blocks into an adiabatic container in thermal contact.

Question

a. Calculate the final temperature
b. Calculate the heat transferred
c. Describe how this is consistent with the first law.
d. Would it be consistent with the 1st law if the gold block cooled and the silver block warmed?
6. Assume you have a 3 mole sample of ideal gas at 1.3atm and 45 °C. Calculate q, w, and ∆U if it is expanded:
a. Reversibly and isothermally to 0.8atm
b. Irreversibly and isothermally against an external pressure of 0.7atm until the volume is 98L
7. Taking the gas in question 6 repeat the process of expanding it isothermally against the external pressure of 0.7atm but do this is 4 steps. Calculate q, w, and ∆U. Comment on the different values you attain in 6a, b and 7.
a. Step 1 expand to 70L against an external P of 1.1atm
b. Step 2 expand to 80L against an external P of 0.9atm
c. Step 3 expand to 90L against an external P of 0.8atm
d. Step 4 expand to 98L against an external P of 0.9atm

Answer 1

a.
[mass Au x specific heat Au x (Tfinal-Tinitial)] + [mass Ag x specific heat Ag x (Tfinal-Tintitial)] = 0
Substitute and solve for Tfinal.

b.
q = [mass Au x specific heat Au x (Tfinal-Tinitial)]
OR
q = ([mass Ag x specific heat Ag x (Tfinal-Tinitial)]
q is the same for each the negative of each other.

c. If you plug in the numbers for part b, one will be + and the other will be the negative of the first. Heat lost = heat gained and that is consistent.

d.
Look at the numbers for c. You will know which cooled and which warmed.