Thermodynamics ppt
- 1. THERMODYNAMICS AND KINETIC THEORY OF GASES MADE BY:- Naman Jain Roll No- A-36
- 2. KINETIC THEORY OF GASES The kinetic theory of gases describes a gas as a large number of small particles (atoms or molecules), all of which are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container. Kinetic theory explains macroscopic properties of gases, such as pressure, temperature, viscosity, thermal conductivity, and volume, by considering their molecular composition and motion. The theory posits that gas pressure is due to the impacts, on the walls of a container, of molecules or atoms moving at different velocities.
- 3. ASSUMPTIONS OF KINETIC THEORY OF GASES • Molecules are moving randomely in all directions. • Molecules exert no appreciable force on one another or on the walls of the container expect during collision. • All collisions between the molecules or with walls of the container are perfectly elastic. • The duration of a collision is negligible in comparison to the time spent between collision. • The average kinetic energy of the gas particles depends only on the absolute temperature of the system. The kinetic theory has its own definition of temperature, not identical with the thermodynamic definition. • The volume occupied by the gas molecules is negligible as compared to the total volume of a gas.
- 4. MAXWELL BOLTZMANN DISTRIBUTION • Maxwell Boltzmann showed that as a result of collision, some molecules are speeded up and some others are slowed down and hence the fraction of molecules possessing a particular speed remains constant . Therefore, the Maxwell-Boltzmann distribution is used to determine how many molecules are moving between velocities v and v + dv. Assuming that the one-dimensional distributions are independent of one another, that the velocity in the y and z directions does not affect the x velocity, for example, the Maxwell-Boltzmann distribution is given by- 𝑑𝑁 𝑁 = (𝑚/2Π𝑘𝑇)1/2 𝑒−𝑚𝑣2/2𝐾𝑇 dV. Where- • dN/N is the fraction of molecules moving at velocity v to v + dv, • m is the mass of the molecule, • kb is the Boltzmann constant, and • T is the absolute temperature.
- 5. MAXWELL BOLTZMANN DISTRIBUTION GRAPH
- 6. RELATED SPEED EXPRESSIONS. • From the Maxwell-Boltzmann distribution, three speed expressions can be derived: the most probable speed, the average speed, and the root- mean-square speed. The most probable speed is the maximum value on the distribution plot. The average speed is the sum of the speeds of all the molecules divided by the number of molecules. The root-mean-square speed is square root of the average speed-squared. • V(mp)= 2𝑅𝑇/√𝑀 • V(avg)= 8𝑅𝑇/√𝜋𝑀 • V(rms)= 3𝑅𝑇/√𝑀 Where- • R is the gas constant, • T is the absolute temperature and • M is the molar mass of the gas. • It always follows that for gases that follow the Maxwell-Boltzmann distribution Vmp<Vavg<Vrms
- 7. EQUIPARTITION THEORAM • The name "equipartition" means "equal division," as derived from the Latin equi from the antecedent, æquus ("equal or even"), and partition from the antecedent, partitionem ("division, portion"). The original concept of equipartition was that the total kinetic energy of a system is shared equally among all of its independent parts, on the average, once the system has reached thermal equilibrium. Equipartition also makes quantitative predictions for these energies. For example, it predicts that every atom of a noble gas, in thermal equilibrium at temperature T, has an average translational kinetic energy of (3/2)kBT, where kB is the Boltzmann constant. As a consequence, since kinetic energy is equal to 1/2(mass)(velocity)2, the heavier atoms of xenon have a lower average speed than do the lighter atoms of helium at the same temperature. U=I/2kT ( Where K is the Boltzmann constant).
- 8. THERMODYNAMICS • Thermodynamics is a branch of physics concerned with heat and temperature and their relation to energy and work. It defines macroscopic variables, such as internal energy, entropy, and pressure, that partly describe a body of matter or radiation. It states that the behaviour of those variables is subject to general constraints, that are common to all materials, not the peculiar properties of particular materials. These general constraints are expressed in the four laws of thermodynamics. Thermodynamics describes the bulk behaviour of the body, not the microscopic behaviours of the very large numbers of its microscopic constituents, such as molecules. Its laws are explained by statistical mechanics, in terms of the microscopic constituents.
- 9. ZEROTH LAW • If two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. • When two systems are put in contact with each other, there will be a net exchange of energy between them unless or until they are in thermal equilibrium. That is the state of having equal temperature. Although this concept of thermodynamics is fundamental, the need to state it explicitly was not widely perceived until the first third of the 20th century, long after the first three principles were already widely in use. Hence it was numbered zero -- before the subsequent three.
- 11. FIRST LAW Energy can neither be created nor destroyed. It can only change forms. • In any process in an isolated system, the total energy remains the same. • A definate amount of mechanical work is needed to produce definate amount of heat and vive versa. W/H= j. where j is called joules constant.
- 12. For a closed system, in any process, the change in the internal energy is considered due to a combination of heat added to the system and work done by the system. Taking as a change in internal energy, one writes- ∆ U= Q – W ( sign convention of clausius) Where Q and W are quantities of heat supplied to the system by its surroundings and of work done by the system on its surroundings, respectively. This sign convention is implicit in Clausius' statement . In modern style of teaching science, however, it is conventional to use the IUPAC convention by which the first law is formulated in terms of the work done on the system. With this alternate sign convention for work, the first law for a closed system may be written: U= Q + W ( sign convention of IUPAC). This convention follows physicists such as Max Planck, and considers all net energy transfers to the system as positive and all net energy transfers from the system as negative, irrespective of any use for the system as an engine or other device. When a system expands in a fictive quasistatic process, the work done by the system on the environment is the product, P dV, of pressure, P, and volume change, dV, whereas the work done on the system is -P dV. Using either sign convention for work, the change in internal energy of the system is: dU=dQ – PdV.
- 13. LIMITATIONS OF FIRST LAW OF THERMODYNAMICS. • No restriction on the direction of the flow of heat: the first law establishes definite relationship between the heat absorbed and the work performed by a system. The first law does not indicate whether heat can flow from a cold end to a hot end or not. • Does not specify the feasibility of the reaction: first law does not specify that process is feasible or not. • Practically it is not possible to convert the heat energy into an equivalent amount of work. • To overcome this limitations, another law is needed which is known as second law of thermodynamics.
- 14. SECOND LAW OF THERMODYNAMICS • In thermodynamics, entropy (usual symbol S) is a measure of the number of specific ways in which a thermodynamic system may be arranged, commonly understood as a measure of disorder. According to the second law of thermodynamics the entropy of an isolated system never decreases; such a system will spontaneously evolve toward thermodynamic equilibrium, the configuration with maximum entropy. Systems that are not isolated may decrease in entropy, provided they increase the entropy of their environment by at least that same amount. Since entropy is a state function, the change in the entropy of a system is the same for any process that goes from a given initial state to a given final state, whether the process is reversible or irreversible. However irreversible processes increase the combined entropy of the system and its environment. • The change in entropy of a system was originally defined for a thermodynamically reversible process as- ∆𝑆 = 𝑑𝑄 𝑟𝑒𝑣 𝑇 . Where T is an absolute temperature of a system.
- 15. CARNOT CYCLE • The Carnot cycle is a theoretical thermodynamic cycle proposed by Nicolas Léonard Sadi Carnot in 1824 and expanded by others in the 1830s and 1840s. It can be shown that it is the most efficient cycle for converting a given amount of thermal energy into work, or conversely, creating a temperature difference (e.g. refrigeration) by doing a given amount of work. • Every single thermodynamic system exists in a particular state. When a system is taken through a series of different states and finally returned to its initial state, a thermodynamic cycle is said to have occurred. In the process of going through this cycle, the system may perform work on its surroundings, thereby acting as a heat engine. A system undergoing a Carnot cycle is called a Carnot heat engine, although such a "perfect" engine is only a theoretical limit and cannot be built in practice.
- 16. EFFICIENCY OF CARNOT CYCLE W= 𝑃𝑑𝑣 = (𝑇 𝐻 - 𝑇𝑐)( 𝑆 𝐵- 𝑆𝐴 ) The total amount of thermal energy transferred from the hot reservoir to the system will be- 𝑄 𝐻 = 𝑇 𝐻 (𝑆 𝐵 - 𝑆𝐴 ) and the total amount of thermal energy transferred from the system to the cold reservoir will be- 𝑄 𝑐 = 𝑇𝑐 (𝑆 𝐵 - 𝑆𝐴 ) The efficiency is defined to be: n= 𝑊 𝑄 𝐻 = 1- 𝑇𝑐 𝑇 𝐻 .
- 17. APPLICATIONS OF THERMODYNAMOCS • All types of vehicles that we use, cars, motorcycles, trucks, ships, aeroplanes, and many other types work on the basis of second law of thermodynamics and Carnot Cycle. They may be using petrol engine or diesel engine, but the law remains the same. • All the refrigerators, deep freezers, industrial refrigeration systems, all types of air- conditioning systems, heat pumps, etc work on the basis of the second law of thermodynamics. • All types of air and gas compressors, blowers, fans, run on various thermodynamic cycles. • One of the important fields of thermodynamics is heat transfer, which relates to transfer of heat between two media. There are three modes of heat transfer: conduction, convection and radiation. The concept of heat transfer is used in wide range of devices like heat exchangers, evaporators, condensers, radiators, coolers, heaters, etc. • Thermodynamics also involves study of various types of power plants like thermal power plants, nuclear power plants, hydroelectric power plants, power plants based on renewable energy sources like solar, wind, geothermal, tides, water waves etc., • Renewable energy is an important subject area of thermodynamics that involves studying the feasibility of using different types of renewable energy sources for domestic and commercial use.
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