Question

A piston-cylinder device whose piston is resting on top of a set of stops initially contains 0.5 kg of helium gas at 100 kPa and 25∘C. The mass of the piston is such that 500 kPa of pressure is required to raise it.

How much heat must be transferred to the helium before the piston starts rising?

Answer 1

Answer:

Q = 1857 kJ

Explanation:

given data

mass helium gas = 0.5 kg

pressure P1 = 100 kPa

temperature T1  = 25°C = 298 K

pressure required P2 = 500 kPa

solution

first we get here final temperature at which piston start rising that is express as

T2 = T1 ×  $\frac{P2}{P1}$      ...........1

put here value we get

T2 = 298 × $\frac{500}{100}$    

T2 = 1490 K

and we know here that untill piston start to rising there is no work done

so as that heat transfer is change in the internal energy

Q = ΔU .........2

Q = m × $c_v$ × ( T2 - T1 )  

Q = 0.5 × 3.1156 × ( 1490 - 298 )  

so Q = 1857 kJ