ThermodynamicsThermodynamics

Thermodynamics is the study of the Thermodynamics is the study of the patterns of energy change.patterns of energy change.

ThermoThermo means means energyenergy

DynamicsDynamics means means Patterns of changePatterns of change

Thermodynamics deals with:Thermodynamics deals with:

a)a) energyenergy

b) The stability of molecules and direction b) The stability of molecules and direction of change.of change.

ExampleExample

Imagine a brick resting on window ledge 3 Imagine a brick resting on window ledge 3 meters high. As the brick rests on the ledge it meters high. As the brick rests on the ledge it

has has potential energy.potential energy.If you knock the brick out of the ledge, the If you knock the brick out of the ledge, the

potential energy is converted to potential energy is converted to kinetic kinetic energyenergy( the brick accelerated towards the ( the brick accelerated towards the

ground).ground).When the brick hits the ground the kinetic When the brick hits the ground the kinetic energy converted to energy converted to light energylight energy (sparks), (sparks),

Sound energySound energy and and chemical energychemical energy (the (the brick breaks).brick breaks).

To study thermodynamics we will To study thermodynamics we will introduce two new terms which areintroduce two new terms which are

1-The system1-The system

2- The surroundings2- The surroundings

Two types of exchange can occur between Two types of exchange can occur between the system and surroundings.the system and surroundings.

1- Energy exchange1- Energy exchange (heat, radiation….etc). (heat, radiation….etc).

22--Matter exchangeMatter exchange (movement of molecules (movement of molecules across the boundry between the system and across the boundry between the system and the surroundings)the surroundings)..

Based on the types of exchange which Based on the types of exchange which take place, three types of systems are take place, three types of systems are identified.identified.

1- Isolated systems1- Isolated systems: no exchange of matter : no exchange of matter or energy.or energy.

2-Open systems2-Open systems: Exchange of both matter : Exchange of both matter and energy.and energy.

3- Closed system3- Closed system: no exchange of matter : no exchange of matter but exchange of energy. but exchange of energy.

The total energy of a system before the process The total energy of a system before the process has taken place, called the has taken place, called the initial state.initial state.

While the total energy of a system after the While the total energy of a system after the process has taken place, calledprocess has taken place, called final state. final state.

The The equilibrium stateequilibrium state is that condition in which is that condition in which no further change is occuring within the system no further change is occuring within the system or between the system and its surroundings.or between the system and its surroundings.

Thermodynamic process are either:Thermodynamic process are either:

--ReversibleReversible: happens slow enough to be : happens slow enough to be reversedreversed

--irreversibleirreversible: can not be reserved: can not be reserved

The first law of thermodynamicsThe first law of thermodynamics

Energy can be exchanged between theEnergy can be exchanged between the

system and its surroundings but the total energy system and its surroundings but the total energy of the system+ the surrounding is constant. i.e of the system+ the surrounding is constant. i.e The energy of the universe, remains constant.The energy of the universe, remains constant.

i. e 1i. e 1stst law of thermodynamics stated that law of thermodynamics stated that

“ “ energy is conserved”energy is conserved”

or “ energy can neither created nor destroyed”or “ energy can neither created nor destroyed”

Heat and work changesHeat and work changes The energy of a system will change if heat is The energy of a system will change if heat is transferred to or from the system or work is transferred to or from the system or work is done by the system.done by the system.

11stst law stated that, if some amount of heat (Q) is law stated that, if some amount of heat (Q) is added into the system, it must either do work or added into the system, it must either do work or increase the total energy of the system.increase the total energy of the system.

In biological systemIn biological system

If the capacity to do work is represented If the capacity to do work is represented by the symbol “W” and “H” stands for by the symbol “W” and “H” stands for enthalpy (or heat content), then the firat enthalpy (or heat content), then the firat law can be expressed as:law can be expressed as:

ΔΔH = Q - WH = Q - W

Isothermal nature of cellular Isothermal nature of cellular processprocess

Although heat is the simplest and more Although heat is the simplest and more familiar medium by which energy may be familiar medium by which energy may be

transferred or used in man-made transferred or used in man-made machines, it is not useful form of energy machines, it is not useful form of energy

for performing biological work.for performing biological work. Why?Why?

“ “ because heat can do work if there is a because heat can do work if there is a temperature differential through which it temperature differential through which it

can act”can act”

Heat must either pass from one body to a Heat must either pass from one body to a second one having lower temperature, or second one having lower temperature, or the temperature of a given hot body is the temperature of a given hot body is lowered.lowered.Since it is not possible that there are very Since it is not possible that there are very small temperature differentials in cells small temperature differentials in cells which is the basis of doing cellular workwhich is the basis of doing cellular work

“ “ living organisms are isothermal”living organisms are isothermal” here we must define another form of energy here we must define another form of energy

called “free energy”.called “free energy”.