Question

When an ideal gas in a cylinder was compressed isothermally by a piston, the work done on the gas was found to be $1.5 \times 10^{4}\mspace{6mu} joules$. During this process about

• A. $3.6 \times 10^{3}$ cal of heat flowed out from the gas
• B. $3.6 \times 10^{3}$ cal of heat flowed into the gas
• C. $1.5 \times 10^{4}$ cal of heat flowed into the gas
• D. $1.5 \times 10^{4}$ cal of heat flowed out from the gas

Answer 1

Answer: (A)

$3.6 \times 10^{3}$ cal of heat flowed out from the gas

Answer 2

In isothermal compression, there is always an increase of heat. which must flow out the gas.

$\Delta Q = \Delta U + \Delta W \Rightarrow \Delta Q = \Delta W\mspace{6mu}\mspace{6mu}(\because\mspace{6mu}\Delta U = 0)$

⇒ $\Delta Q = - 1.5 \times 10^{4}J = \frac{1.5 \times 10^{4}}{4.18}cal = - 3.6 \times 10^{3}cal$