Question

If the amount of heat given to a system be $35$ joules and the amount of work done by the system be $-50$ joules, then the changes in the internal energy of the system is:

• A. $-50$ joules
• B. $20$ joules
• C. $85$ joules
• D. $50$ joules

Answer 1

Answer: (C)

$85$ joules

Given: Heat given to system($△Q$)=35 J, Work don by the system($W$) = -50 J.

Solution:

From first law of thermodynamics, $△Q=△U+W$,

$\therefore △U=△Q-W$

$\therefore △U=35-(-50)=85J$

Hence correct option is C.