Thermodynamics : The branch of science which deals with conversion of heat into other forms of energy or vice-versa .
Thermodynamic Process : If the state of a system changes in such a way that any of P , V , T etc . changes , the process is called Thermodynamic Process .
Zeroth Law of Thermodynamics:
If two bodies A and B are in thermal equilibrium and A and C are also in thermal equilibrium, then B and C are also in thermal equilibrium.
Prevost Theory of Exchanges:
According to this theory, every body is continuously emitting radiant energy in all directions at a rate depending only on the nature of its surface and its temperature and it is absorbing radiant energy from all surrounding bodies at a rate depending on its surface and the temperature of the surrounding bodies.
Mechanical Equivalent of Heat:
Whenever mechanical work is transformed into heat or heat into mechanical work, there is a constant ratio between the work and the amount of heat. This ratio is called “mechanical equivalent of heat” and is denoted by J .
Thus, if W be the amount of work done and Q the amount of heat produced, we have
W/Q = J ,
⇒ W = JQ
If Q = 1 unit then J = W . Therefore , J is numerically equal to the mechanical work required to produce one unit of heat.
Work done by the Gas :
Small amount of work done dW in moving a piston by small distance dx is
dW = F dx
dW = P. A . dx
dW = P. dV
$\displaystyle W = \int_{V_1}^{V_2}P .dV $
First law of Thermodynamics :
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
In differential form dQ = dU + dW
Q = + ve ⇒ Heat is supplied to the gas
Q = – ve ⇒ Heat is taken out from the gas
dQ = n C dT ; Where C = molar specific heat
C = Cp (constant pressure); C = Cv =(constant volume)