Prepared
by Dr. A. Mekki

Summary of chapter
19

** **

1.
If
two bodies are in **thermal equilibrium**
with each other they must have **the same
temperature**.

*2.
**The Zeroth-law of thermodynamics states that if two bodies A and B are
separately in thermal equilibrium with a third body, C,*

* then A and B are in thermal equilibrium
with each other when placed in thermal contact.*

3.
Change
of temperature scale:

*T _{C}
= T_{K} 273 *

* *

*T _{F}
= 9/5 T_{C} + 32 *

* *

*T _{K}
= 5/9 T_{F} + 255*

**Important:** _{} and
_{}

4.
When
a substance is heated, it generally expands. The change in length, *D**L* is related to the change in
temperature *D**T*

and the
proportionality constant is called a (coefficient of linear expansion)

5.
Expansion and contraction of a __solids__

Ø In one dimension

The change in length is given
by _{} and

The final length is _{}

*L _{i}* is the

The change in the area is
given by _{} and

The final area is _{}

The change in
the volume is _{} and

The final volume
is

_{}** This equation is valid for
solids and liquids**.

Coefficient of
volume expansion _{}.

6.
The
heat gained or lost by a substance is given by:

(i)
If there is a change in temperature and there is no change in the phase

_{}

c is the
specific heat of the substance and *D**T = T _{f} - T_{i}*

(ii)
If there is
a change in phase and the temperature of the system remains the same

_{}

L is called the heat of transformation.

If there is fusion (solid liquid), then we use L_{f}, if there is vaporization
(liquid gas), then we use L_{v}.

7.
This
section is related to GASES ONLY

A gas may exchange energy with
the surroundings through work.

The work done ** on **or

_{}

* *

*The work can also be
calculated from a PV diagram.*

The work is the **area
under the curve** in a PV diagram as shown in the above
figure.

For a cyclic process the work ** is the area enclosed** by the cycle.

8.
The first law of thermodynamics is the law of ** conservation of energy **and given by

_{}

where
*DE*_{int} is the internal
energy of the gas.

* *

Ø *Q > 0 if the gas absorbs (gains) heat*

Ø *Q < 0 if the gas expels (lose) heat*

Ø
*W > 0 if the gas
does work*

Ø
*W < 0 if external
work is done on the gas*

* *

9.
Special cases of the first
law of thermodynamics

Ø ** Adiabatic process: **Q
= 0 and

* *

Ø ** Constant volume process: **W = 0 and

* *

* *

* *

* *

* *

* *

Ø *Cyclic process: **DE*_{int} = 0, *Q = W*

* *

* *

* *

* *

* *

* *

* *

Ø *Free expansion: **DE _{int}
= Q = W = 0*

* *

10.
Heat can be transferred
between a system and the environment in three ways; by **conduction, **by** convection, **and
by** radiation**.

Ø *In the case of transfer of heat by conduction, the rate of
heat flow is given by:*

_{} (Watts)

* *

*k is the thermal conductivity of the material through
which heat is conducted.*

* *

* *

Ø *Radiation is heat transfer through the emission of
electromagnetic energy. The power of the radiating heat source is given by:*

* *

**_{} **(Watts)

* *

* **s = 5.6703 ** 10 ^{-8}
W/m^{2}K is Stefan-Boltzman constant.*

* **e is the emissivity of the object and A is
its surface area of the heat source. *

* T
is the temperature in Kelvin.*

* *

* *