Thermodynamics

By: Yong Yu Wen (33)

303

What is it?

•is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency.”

Definition

•the concise definition of the subject was first given by a Scottish physicist, William Thomson in 1854

History

•thermodynamics concerns energy transfer to or from a thermodynamic system.

•a thermodynamic system is any collection of objects that is convenient to regard as a unit, and that may have the potential to exchange energy with its surroundings.

Thermodynamic system

Laws of Thermodynamics

system of laws that describe the transport of heat and work in thermodynamic

processesclaim that energy can be

exchanged between physical systems as heat or work.

claim the existence of a quantity named entropy

Laws of Thermodynamics have become some of the most important fundamental laws in physics and other sciences associated with thermodynamics

four laws

the zeroth law underlies the basic definition of temperature

Laws of Thermodynamics

the second law states that the entropy of an

isolated macroscopic system never decreases, or that perpetual

motion machines are

impossiblethe third law concerns

the entropy of a perfect crystal at absolute zero temperature, and which

implies that it is impossible to cool a

system all the way to exactly absolute zero

the first law mandates

conservation of energy, and

states in particular that

the flow of heat is a form

of energy transfer

there have been suggestions of additional laws, but none of them have anything like the generality of the accepted laws, and they are not mentioned in standard textbooks

Zeroth law

coined by Ralph H. Fowler in the 1920s

the most fundamental of the four numbered laws of thermodynamics

called the zeroth law because the need to state it explicitly was not understood until after the First, Second, and Third Laws had been named and become commonplace

coined by Ralph H. Fowler in the 1920s

the most fundamental of the four numbered laws of thermodynamics

called the zeroth law because the need to state it explicitly was not understood until after the First, Second, and Third Laws had been named and become commonplace

Zeroth law generalization principle of the thermal equilibrium among bodies, or thermodynamic systems, in contact

it results from the definition and properties of temperature

a system is said to be in thermal equilibrium when its temperature does not change over time

often claimed that we can define a temperature function or more informally, that we can "construct a thermometer."

in the space of thermodynamic parameters, zones of constant temperature will form a surface, which provides a natural order of nearby surfaces

Zeroth law

the temperature so defined may indeed not look like the Celsius temperature scale, but it is a temperature

function nonetheless

the dimensionality of a surface of constant temperature is one less than the number of

thermodynamic parameters

it is then simple to construct a global temperature function that provides a continuous ordering of states

First law

• an expression of the principle of conservation of energy

•states that energy can be transformed ,but cannot be created or destroyed

•in any process in an isolated system, the total energy remains the same

•for a thermodynamic cycle the net heat supplied to the system equals the net work done by the system

First law

formulated by saying that the change in the internal energy of a system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings

First law the first explicit statement of the first law of thermodynamics

was given by Rudolf Clausius in 1850

“There is a state function E, called ‘energy’, whose differential equals the work exchanged with the surroundings during an adiabatic process."

First law the First Law clarifies the nature of energy

it is a stored quantity which is independent of any particular process path

if a system undergoes a thermodynamic cycle, whether it becomes warmer, cooler, larger, or smaller, then it will have the same amount of energy each time it returns to a particular state

First law mathematically speaking, energy is a state function and

infinitesimal changes in the energy are exact differentials

the first law can be expressed as the fundamental thermodynamic relation

heat supplied to a system = increase in internal energy of the system + work done by the system

increase in internal energy of a system = heat supplied to the system - work done by the system

First law example:

Second law an expression of the universal principle of decay observable

in nature

measured and expressed in terms of a property called entropy

it stats that the entropy of an isolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium

Second law in short, heat can spontaneously flow from

a higher-temperature region to a lower-temperature region, but not the other way around

example: a cup of hot coffee left on a table eventually cools, but a cup of cool coffee in the same room never gets hot by itself

entropy change dS of a system undergoing any infinitesimal reversible process is given by δq / T

δq is the heat supplied to the system and T is the absolute temperature of the system

Second law

the origin of the second law can be traced to French physicist Sadi Carnot's 1824 paper Reflections on the Motive Power of Fire

which presented the view that motive power (work) is due to the flow of caloric (heat) from a hot to cold body (working substance)

Second law

in simple terms, the second law is an expression of the fact that over time, differences in temperature, pressure, and chemical potential tend to even out in a physical system that is isolated from the outside world

entropy is a measure of how much this evening-out process has progressed

Second law

there are many versions of the second law, but they all have the same effect, which is to explain the phenomenon of irreversibility in nature

Third law

a statistical law of nature regarding entropy and the impossibility of reaching absolute zero of temperature

most common statement: “As a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.”

in short, entropy is temperature dependent and results in the formulation of the idea of absolute zero

Third law developed by the chemist Walther Nernst, during the years 1906-

1912, and is thus sometimes referred to as Nernst's theorem or Nernst's postulate

an alternative version of the third law: “If the entropy of each element in some (perfect) crystalline state be taken as zero at the absolute zero of temperature, every substance has a finite positive entropy; but at the absolute zero of temperature the entropy may become zero, and does so become in the case of perfect crystalline substances. “

this law provides an absolute reference point for the determination of entropy

the entropy determined relative to this point is the absolute entropy

Third law

in simple terms, the Third Law states that the entropy of most pure substances approaches zero as the absolute temperature approaches zero

References

en.wikipedia.org/wiki/Thermodynamicsweb.mit.edu/16.unified/www/FALL/thermodynamics/index.htmlwww.taftan.com/thermodynamics/ www.shodor.org/unchem/advanced/thermo/