(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

1. A large closed bag of plastic contains 0.10 m3 of an unknown gas at an initial temperature of 10°C and at the same pressure as the surrounding atmosphere, 1.0 atm. You place this bag in the sun and let the gas warm up to 38°C and expand to 0.11 m3. During this process, the gas absorbs 840 cal of heat. Assume the bag is large enough so the gas never strains against it, and therefore remains at a constant pressure of 1.0 atm.

(a) How many moles of gas are in the bag?

(b) What is the work done by the gas in the bag against the atmosphere during the expansion?

(c) What is the change in the internal energy of the gas in the bag?

(d) Is the gas a monoatomic gas? A diatomic gas?

2. Relevant equations

3. The attempt at a solution

a.)

PV=nRT --> 1 atm * .10 m^3= n * 0.0821 * (10+273)K

n=.1/23.2343--->0.004304 moles

b.)

W=P*deltaV--->1 atm*.01m^3 = .01 Joule

c.) delta U= Delta Q - delta W --> (840 cal*4.186J)-0.01 J

delta U=3516.24 J-0.01J=3516.23J

d.)

delta Q = nc_{p}*delta T --> 3516.23J=0.004304 mol * c_{p}*28K

c_{p}=29177.4 Joules

I think part D is where my problem lies. The bold number I think is especially off. Am I approaching this problem the right way? My book doesn't give any good examples....Thanks.

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# How many moles of gas are in the bag?

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