Question

A gas absorbs $250J$ of heat and expands from $1$ litre to $10$ litre at constant temperature against external pressure of $0.5$ atm. The values of $q$, $w$ and $△U$ will be respectively:

• A. $-250J,455J,710J$
• B. $250J,-455J,-205J$
• C. $-250J,-455J,-205J$
• D. $-250J,455J,205J$

Answer 1

The correct option is B $250J,-455J,-205J$

$q=+250J(+ve$ because heat is supplied to the system$)$

$w=-P_{ext}△V$

$=-0.5\times 101325(10\times {10}^{-3}-{10}^{-3})[\because 1atm=101325P\&1l={10}^{-3}m]$

$w=-455J$

$△U=q+w$

$△U=-205J$