Question

A cylinder, which is in a horizontal position, contains an unknown noble gas at 48400 Pa and is sealed with a massless piston. The piston is slowly, isobarically moved inward 18.9 cm, which removes 18600 J of heat from the gas. If the piston has a radius of 27.2 cm, calculate the change in the internal energy of the system Δ U

Answer 1

Solution :

Given :

P = 48400 Pa

L = 18.9 cm = 0.189 m

Q = -18600 J

And, r = 27.2 cm = 0.272 m

Here, Work done by the gas in isobaric process (Because Pressure inside the cylinder remains constant)

W = P V = P( - A L) = - P (r²) L = -( 48400 Pa)()(0.272 m)²(0.189 m) = - 2126.15 J

Now According to the first law of thermodynamics :

  Q = W + U

  U = Q - W

  U = ( - 18600 J) - ( - 2126.15 J)

  U = -16473.845 J = - 16474 J