Consider 0.8 grams of air (which may be assumed to be an ideal gas) at 295 K and

Question

Consider 0.8 grams of air (which may be assumed to be an ideal gas) at 295 K and 1.5 bar trapped in a rigid tank. An electrical heater is operated for 30 seconds. During this time the voltage across the heater is 12 V and 0.6 amps pass through the resistance element. During this process, 126 J of energy is lost via heat transfer through the tank walls.
a. Assuming the specific heats of air are constant (at the 300 K values) determine the final temperature of the air. ans. 317 K
b. Determine the final pressure in the tank.

Explanation / Answer

Net heat input = VIt = 12*0.6*30 = 216 J Heat lost= 126 J so net heat input = 90 J so this heat = mCv*change in temp. final temp=change in temp+ initial temp. also final pressure can be then calculated as T and V are known.

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