Question

If the work done by a system on its sorrounding
is 100J and the increase in the internal energy
of the system is 100 cal what must be the
heat supplied to the systema
(Given if 4.186J/cal)​

Answer 1

Answer:

Correct option is

D

120 J

Solution:- (D) 120J

As the work is done by the system and heat is supplied to the system.

Therefore,

q=100 cal=420J

w=−300J

Now from first law of thermodynamics,

ΔU=q+W

∴ΔU=420+(−300)

⇒ΔU=120J

Hence the change in internal energy during the process is 120J.

Answer 2

Given:

• Work done by system = 100 J
• Increase in internal energy = 100 cal

To find:

• Heat supplied ?

Calculation:

In this type of questions, it is best to apply first law of thermodynamics as follows :

$\Delta H = \Delta U + W$

• Now, work is done by system, so sign of W will be positive.

• Internal energy is increased, so ∆U sign is positive.

• 100 cal = 100/4.18 = 23.88 J

$\implies\Delta H = 23.88 + 100$

$\implies\Delta H = 123.88 \: joule$

So, the heat supplied to system is 123.88 Joule.