A gas present in a cylinder fitted with a frictionless piston expands against a constant pressure of 1 atm from a volume of 2 litre to a volume of 6 litre. In doing so, it absorbs 800 J heat from surroundings. Determine increase in internal energy of process.

Question

A gas present in a cylinder fitted with a frictionless piston expands against a constant pressure of 1 atm from a volume of 2 litre to a volume of 6 litre. In doing so, it absorbs 800 J heat from surroundings. Determine increase in internal energy of process. (A)  (B)  (C)  (D)

Tardigrade Admin · Accepted Answer

Since, work is done against constant pressure and thus, irreversible.
Given,

Δ V = (6 - 2) = 4 L; P = 1

atm

∴ W = - 1 \times 4 L - a t m

= - \frac{1 \times 4 \times 1.987}{0.0821}

cal
(since

0.0821 L - a t m = 1.987

cal)

= - 96.81

cal

= - 96.81 \times 4.184 J (∵ 1 c a l = 4.184 J)

= - 405.05 J

Now from

I^{s t}

law of thermodynamics

q = Δ U - W

800 = Δ U + 405.05

∴ Δ U = 395 J

Q. A gas present in a cylinder fitted with a frictionless piston expands against a constant pressure of 1 atm from a volume of 2 litre to a volume of 6 litre. In doing so, it absorbs 800J heat from surroundings. Determine increase in internal energy of process.

Q. A gas present in a cylinder fitted with a frictionless piston expands against a constant pressure of $1$ atm from a volume of $2$ litre to a volume of 6 litre. In doing so, it absorbs $800 J$ heat from surroundings. Determine increase in internal energy of process.