Question

A system absorbs 300 Cal of heat with the result of that, the volume of the system becomes double of the initial volume and temperature changes from 273K to 546K. The work done by the system on the surrounding is 200 cal. Calculate $\Delta E$.

Answer 1

Hint In order to calculate the change in internal energy of the system, we must first know about the First law of thermodynamics. The heat absorbed and the work done is already given, so by using the equation of First law of thermodynamics the change in the internal energy is calculated easily.

Complete step by step solution:
Let us first understand what a First law of thermodynamics is. According to the First law of thermodynamics, we can say that heat is a form of energy which can be neither created nor destroyed but can be transformed from one form to another form. The equation is given as
$\Delta E = q + w$
Where $\Delta E$is the internal energy change of the system.
q is the heat absorbed
w is the work done
In the question the value of q and w is given:
q = + 300cal
w = - 200cal as the work is done by the system
Therefore, the change in the internal energy is given as
$\Delta E = 300 + ( - 200) = 300 - 200 = 100cal$
The change in the internal energy of the system is found to be 100cal.

Note: First law of thermodynamics will only tell us about the conversion of energy from one form to another. It will not tell us about the direction in which the reaction is taking place. In order to know about the direction, we are using the second law of thermodynamics.