Download First Law Of Thermodynamics

Thermodynamics
Thermodynamics is the study of the
patterns of energy change.
Thermo means energy
Dynamics means Patterns of change
Thermodynamics deals with:
a) energy
b) The stability of molecules and direction
of change.
Example
Imagine a brick resting on window ledge 3
meters high. As the brick rests on the ledge it
has potential energy.
If you knock the brick out of the ledge, the
potential energy is converted to kinetic
energy( the brick accelerated towards the
ground).
When the brick hits the ground the kinetic
energy converted to light energy (sparks),
Sound energy and chemical energy (the
brick breaks).
To study thermodynamics we will
introduce two new terms which are
1-The system
2- The surroundings
Two types of exchange can occur between
the system and surroundings.
1- Energy exchange (heat, radiation….etc).
2-Matter exchange (movement of molecules
across the boundry between the system and
the surroundings).
Based on the types of exchange which
take place, three types of systems are
identified.
1- Isolated systems: no exchange of matter
or energy.
2-Open systems: Exchange of both matter
and energy.
3- Closed system: no exchange of matter
but exchange of energy.
The total energy of a system before the process
has taken place, called the initial state.
While the total energy of a system after the
process has taken place, called final state.
The equilibrium state is that condition in which
no further change is occuring within the system
or between the system and its surroundings.
Thermodynamic process are either:
-Reversible: happens slow enough to be
reversed
-irreversible: can not be reserved
The first law of thermodynamics
Energy can be exchanged between the
system and its surroundings but the total energy
of the system+ the surrounding is constant. i.e
The energy of the universe, remains constant.
i. e 1st law of thermodynamics stated that
“ energy is conserved”
or “ energy can neither created nor destroyed”
Heat and work changes
The energy of a system will change if heat is
transferred to or from the system or work is
done by the system.
1st law stated that, if some amount of heat (Q)
is added into the system, it must either do work
or increase the total energy of the system.
In biological system
If the capacity to do work is represented
by the symbol “W” and “H” stands for
enthalpy (or heat content), then the firat
law can be expressed as:
ΔH = Q - W
Isothermal nature of cellular
process
Although heat is the simplest and more
familiar medium by which energy may be
transferred or used in man-made
machines, it is not useful form of energy
for performing biological work.
Why?
“ because heat can do work if there is a
temperature differential through which it
can act”
Heat must either pass from one body to a
second one having lower temperature, or
the temperature of a given hot body is
lowered.
Since it is not possible that there are very
small temperature differentials in cells
which is the basis of doing cellular work
“ living organisms are isothermal”
here we must define another form of energy
called “free energy”.