Question

The work done by a system is 8 J when 40 J heat is supplied to it. The change in internal energy of the system during the process:
A. 32 J
B. 40 J
C. 48 J
D. -32 J

Answer 1

Hint: In this question we have been asked to calculate the change in internal energy of the system, when the work done by a system when 40 J heat is supplied is 8 J. Therefore, we know that work done by the system is 8 J and the heat supplied to the system is 40 J. We also know that change in internal energy is given as the sum of work done by the system and heat supplied. Therefore, using this concept we shall calculate the change in internal energy of the given system.

Formula used:
\[\Delta U=Q+W\]
Where,
U is the internal energy
Q is the heat supplied
W is the work done by the system.

Complete step by step solution:
It is given that the work done by a system is 8 J. It is also given that the heat supplied to the system is 40 J. now, since the heat is supplied to the instead, using sign and conventions the heat supplied to the system say Q is given as,
\[Q=-40J\]
And work done \[W=8J\]
We know that the change in internal energy is given as the sum of work done by the system and the heat supplied.
\[\Delta U=Q+W\]
After substituting the given values
We get,
\[\Delta U=-40J+8J\]
On solving,
\[\Delta U=-32J\]

Therefore, the correct answer is option D.

Note:
The energy associated with disordered and random motion of molecules is known as internal energy. It is mostly the sum of kinetic and potential energy due to motion of molecules. It is an extensive property. The internal energy depends on the size of the system. The potential and kinetic energy are always converted into one another at temperature greater than absolute zero, however the sum is always constant.