Question

In a certain process, 500J of work is done on a system which gives off 200J of heat. what is the value of change in internal energy for the process?

Answer 1

Given :

Work done on the system (W) = 500 J

Heat (Q) = 200 J

To Find :

The value of change in internal energy

Solution :

According to the First law of thermodynamics,

Change in internal energy (ΔU) = Heat (Q) + Work Done (W)

As work is done 'on the system' hence (W) will be positive.

As Heat is 'evolved by the system' hence (Q) will be negative.

Thus, Change in internal energy (ΔU) =  -Q + W

                                                              = -200 + 500

                                                              = 300 J

Therefore, the change in the internal energy for the process is 300 J.

Answer 2

Answer:

The change in Internal Energy for the process is 300J.

Explanation:

Given that,

500J of work is done on the system and it releases 200J of heat.

The sign conventions followed in chemistry is as follows:

• positive if work is done on the system and negative if work is done by the system.
• Positive if heat is supplied to the system and negative if heat is released by the system.

And from the First Law of Thermodynamics we have,

ΔInternal Energy(U)=ΔHeat(Q)+ΔWork(W)

i.e., ΔU=ΔQ+ΔW

From the above data and following the sign conventions we can write,

Heat, ΔH=-200 and Work, ΔW=500

∴ ΔU= -200+500

⇒ ΔU=300J.