In a thermodynamic process the pressure of a fixed mass of a gas is changed in such a manner that the gas molecules give out $$30$$ J of heat and $$10$$ J of work done on the gas. If the initial internal energy of the gas was $$40$$ J. Then the final internal energy will be ?

Question

Infinity Learn · Accepted Answer

first law of thermodynamics is $$dQ=dU+dWdQ$$ is heat energy $$=-30J$$  $$(-ve$$ since heat given out by $$system)dW$$ is work done $$=$$ $$-10J$$ $$(-ve$$ since work is done on $$system)dU$$ is change in internal $$energy=Uf-Uii=Ufinal-Uinitial$$ here $$Ui=40J$$  substitute the values in first law of thermodynamics  $$dQ=$$[$$Uf-Ui$$]$$+dW$$ ⇒$$-30=$$[Uf−$$40$$]−$$10$$ ⇒$$-30+50=Uf$$ ⇒$$Uf=20$$ J

In a thermodynamic process the pressure of a fixed mass of a gas is changed in such a manner that the gas molecules give out 30 J of heat and 10 J of work done on the gas. If the initial internal energy of the gas was 40 J. Then the final internal energy will be ?

Remember concepts with our Masterclasses.

Ready to Test Your Skills?

free study material