A) The internal energy of a system changes because the system gains 178 J of hea
ID: 1297162 • Letter: A
Question
A) The internal energy of a system changes because the system gains 178 J of heat and performs 348 J of work. In returning to its initial state, the system loses 113 J of heat. During this return process, what work is involved? If the work is done by the system, then give the work involved as a positive number. If the work is done on the system, then give the work involved as a negative number. (in Joules)
B) Six grams of helium (molecular mass = 4.0 u) expand isothermally at 350 K and does 8700 J of work. Assuming that the helium is an ideal gas, determine the ratio of the final volume of the gas to the initial volume. (no units)
Please give full answers to four significant figures without rounding.
Explanation / Answer
E --- change in internal energy
q --- heat gained or lost
w ---work done by the system
E = q + w
work done by the system w is negative
E= 178 + (-348) = -170
Increase in internal energy in the first process means decrease in the second process
170 = (-113) + w
w = -283 J
----------------------------------------------------
Helium = 1.5 moles
W= nRT ln V2/V1
8700 = 1.5 x 8.314 x 350 ln [ V2/V1 ]
ln [ V2/V1 ] = 1.99
V2/V1 = e1.99
= 7.33
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