Examkrackers Chemistry question (#58, pg140)

[robrobbberts]

A certain Carnot engine requires 18 Kg of water in the form of steam as its working substance. When 5 x 10^5 J of heat energy are added at a constant temperature of 400 K the gas expands to 4 m^3. What is the approximate pressure of the gas after the initial expansion? (The ideal gas constant is R = 8.314 J/K mol)

A. 8.3 x 10^5 Pa
B. 8.3 x 10^7 Pa
C. 1.3 x 10^8 Pa
D. 1.3 x 10^8 Pa


I understand to use PV = nRT, but my conversion from atm to Pa is not working. 1 atm = about 10^5 Pa . Right?

so why is the answer A? The answer in the back of the book doesnt convert anything. So if you use the 8.314 number to solve for P, you get the answer in Pa? But if you would use the .08206 number, you would get atm?

i'm confused.

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[BloodySurgeon]

So if you use the 8.314 number to solve for P, you get the answer in Pa? But if you would use the .08206 number, you would get atm?

Yep!

Gas Constant R = 8.3145 J·mol-1·K-1 = 0.0821 L·atm·mol-1·K-1

 

[robrobbberts]

Yep!

Gas Constant R = 8.3145 J·mol-1·K-1 = 0.0821 L·atm·mol-1·K-1

:lol Thanks! I never learned that in my Chemistry class, and the review books didn't mention this.