Internal Energy Formula

Internal Energy Formula is the heat energy stocked in gas. If a certain amount of heat is applied to gas, the result is that the temperature of the gas may increase or else the volume of gas might increase. In this manner doing some work externally or volume and temperature may both intensify, but it will be made definite by the situations under which the gas is provided heat.

When the structure is left in a situation which differs from its condition before the process, after the process, it can be articulated as

ΔU  = Q – W

(U2 – U1) = Q – W


Q = (U2 – U1) + W


Q = Total amount of heat the device receives from its surroundings.

W = Total work done by the system.

U1 is termed as the internal energy of the system at the commencement of the procedure, and the internal energy at the culmination of the procedure is U2.

The first law thermodynamics for a closed system can be written as

ΔU  = Q + W

Solved Examples

Problem 1: Calculate the difference in the internal energy of the working fluid stating whether it is a loss or gain in an internal combustion engine, the heat rejected to the cooling water during the compression stroke is 80 KJ/kg and the work input is 200 KJ/kg.


Heat rejected to the cooling water

Work input W = – 200 KJ/kg

Q = – 80 KJ/kg

Using the formula,

Q =  ΔU – W

– 80 =  ΔU – 100

ΔU = – 80 + 200

ΔU = 120 KJ/kg

Therefore, the increases in internal energy ΔU = 120 KJ/kg.

To know more examples and practice questions on Internal Energy Formula, please visit Byju’


Leave a Comment

Your Mobile number and Email id will not be published.