A gas can be taken from A to B via two different processes ACB and ADB. When path ACB is used 60 J of heat flows into the system and 30 J of work is done by the system. If path ADB is used work done by the system is 10 J. The heat flow into the system in path ADB is:

A gas can be taken from A to B via two different processes ACB and ADB. When path ACB is used 60 J of heat flows into the system and 30 J of work is done by the system. If path ADB is used work done by the system is 10 J. The heat flow into the system in path ADB is: Correct Answer 40 J

Concept:

First Law of Thermodynamics:

The First Law of Thermodynamics states that heat is a form of energy, and thermodynamic processes are therefore subject to the principle of conservation of energy.

The formula is given by

ΔU = ΔQ – W

According to First law of Thermodynamics, the change in the internal energy used in path ACB,

ΔU = ΔQ_ACB – ΔW_ACB

Calculation:

Work done by the system in path ACB, ΔW_ACB = 30 J

Work done by the system in path ADB, ΔW_ADB = 10 J

Heat added to the system in path ACB, ΔQ_ACB = 60 J

Heat imported to a body is generally used to increase internal energy and work done against external pressure.

⇒ (U_B – U_A) = ΔQ_ACB – ΔW_ACB

= 60 – 30 = 30 J

Now, (U_B – U_A) = 30 J

To find the heat flow in the system in path ADB is

⇒ ΔQ_ADB = ΔU + ΔW_ADB

⇒ ΔQ_ADB = (U_B – U_A) + ΔW_ADB

By substituting the values in the above equation, we get

⇒ ΔQ_ADB = 30 + 10