Question

What is change in internal energy of a system, if 20 J of heat is supplied to it and 25 J of work is done by it?​

Answer 1

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dU = dq + w

dU = -20 J + (-60 J) = -80 J

Internal energy of system is decreased by 80 Joules.

Answer 2

Given:

• Heat supplied = 20 Joules
• Work done = 25 Joules

To find:

• Change in internal energy?

Calculation:

In this type of questions, it is best to apply the first law of thermodynamics.

The general equation is :

$\boxed{\Delta Q = \Delta U + W}$

• Since heat is supplied to the system, the sign of ∆Q will be positive.

• Since work is done by the system, the sign of W will be positive.

Putting necessary values :

$\implies ( + 20)= \Delta U + ( + 25)$

$\implies \Delta U =20 - 25$

$\implies \Delta U = - 5 \: joule$

So, change in internal energy is -5 Joule.