Heat flow and the first law of thermodynamics. Lecture 6

Lecture 6

Heat flow and the first law of thermodynamics.
Kind of

Heat

When the temperature of a thermal system in contact with a

Mechanical equivalent of heat

Mechanical energy is not conserserved in the presence

Specific heat capacity

The heat capacity C of a particular sample of

Energy transfer and specific heat capacity

From this definition, we can relate

Dependence of specific heat capacity on temperature

Specific heat varies with temperature.

Dependence of specific heat capacity on volume and pressure

Measured values of

Phase transition

It can be that transfer of energy does not result

Latent heat

Quantitative measure of phase transition is latent heat L:
Q=±mL
Latent heat

State variables - Thermodynamic process - Thermal equilibrium

We describe the

Work and heat in thermodynamic process

The total work done by the

Work depends on the path:

(a): Wa= Pi(Vf-Vi)
(b): Wb= Pf(Vf-Vi)
1) Wa< Wb

Two ways of energy transfer

There exist two ways in which energy

The First Law of Thermodynamics

The change in internal energy ΔU of

The first law of thermodynamics is a special case of the

Ideal Gas Processes

Here W is work done by the system,
ΔQ

Adiabatic (no heat flow, Q=0):
ΔW = -ΔU
The curve of adiabatic process

Polytropic processes

PVγ = const, γ=const.
Isobaric γ=0
Isotermic γ=1
Adiabatic γ= CP/CV
Isochoric γ=∞

Cyclic Processes

If a nonisolated system is performing a cyclic process, the