First Law of Thermodynamics – NEET

First Law of Thermodynamics

The amount heat absorbed by the system is equal to the change in it’s interval energy and work done by the system.
It is the consequence of conservation of energy for gaseous system.

Heat supplied to the gas = Increase in internal energy + work done by the gas.

Q=ΔU+W   Q=+ve ⇒ heat is supplied to the gas
in differential form dQ=dU+dW  Q=-ve⇒heat is taken out from the gas
and dQ=nCdT   = molar specific heat

C=C_P (constant pressure);  C=C_v =(constant volume)
and  dU=d[(f/2)nRT]  f = degree of freedom

dU=(f/2)nRdT  dU=+ve for increase in temperature

dU=–ve for decrease in temperature

dW=∫_(V_1)^(V_2)▒PdV (P = pressure of the gas of which work is to be calculated)

W=+ve for work done by gas  (in expansion of gas)

W=–ve for work done by gas  (in contraction of gas)

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