Question

The change in internal energy of a thermodynamical system which has absorbed 5000 cal of heat and does 5000 J of work is A) Zero B) 16000 J C) 21000 J D) 10000 J​

Answer 1

Given:

The thermodynamical system has absorbed 5000 cal of heat and does 5000 J of work.

To find:

Change in internal energy ?

Calculation:

First convert unit of calorie to joule:

• 5000 cal = 5000 × 4.2 = 20920 J.

Applying 1st Law of Thermodynamics :

$\sf \: \Delta Q = \Delta U + W$

• System has absorbed heat, so sign of ∆Q will be positive.

• System does work , so sign of W will also be positive.

$\sf \implies\: + 20920= \Delta U + ( + 5000)$

$\sf \implies\: 20920= \Delta U + 5000$

$\sf \implies\: \Delta U = 20920 - 5000$

$\sf \implies\: \Delta U = 15920 \: joule$

$\sf \implies\: \Delta U \approx 16000 \: joule$

So, change in internal energy is 16000 Joule