What Is Thermo-dynamics - Research Paper Example

 William Thomson, a Scottish expert in physics explained thermodynamics in the year 1854 in the these words, “Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, and the relation of heat to electrical agency.” Thermodynamics is the aspect of physics which explains the relationship of the changes in heat energy with relation to the work done and the changes observed in other properties of a substance such as the temperature, volume and pressure. It deals with the factors of shift of energy from one point to another as well as the change in the forms of energy. This aspect of physics works towards increasing the efficacy of systems which use heat. A steam turbine can be used as an example to explain the principles of thermodynamics. The steam turbine is driven mainly by steam and it is the heat energy from the steam which is converted into work and is utilized by the turbine. The application of thermodynamics is vast and it can be applied to simple systems for example the bicycle pump as well as to very complex systems like a nuclear reactor. The concept of thermodynamics is based on the laws of thermodynamics which explain the principles of the energy changes. The relationship between different physical systems is also understood by the concept of thermodynamics. System and surroundings are also two important notions of thermodynamics. There are different types of thermodynamic processes that occur which include adiabatic process, isochoric process, isobaric process and isothermal process. Each of these processes has one factor constant which does not change throughout the course of the thermodynamic process and these factors include heat, volume, pressure and temperature respectively. (Potter 2009, Kondepudi 2008, Arora 1998 & Enrico 1956) BASIC CONCEPTS OF THERMODYNAMICS Internal Energy: A system or a body which has the capability of performing work is considered to have energy. Different forms of energy exist with potential and kinetic energy being examples. Examples of systems that utilize energy include a nuclear plant where electrical energy is yielded by means of nuclear energy and a turbine which has the capability of utilizing heat energy and converting it into mechanical energy. In a thermodynamic system, the total energy possessed by the system is referred to as its internal energy. The main types of energy in this system are the potential energy and the kinetic energy. The kinetic energy is due to the movement of the molecules in the system and the potential energy occurs due to the changing positions of the molecules in the system. The internal energy of the entire thermodynamic system is found rather than of particular substances. Thus this serves to be a measure of the thermodynamic system. Also this energy is calculated assuming a reference point which is assumed to be zero. Enthalpy: Enthalpy is defined as the product of pressure and volume added in the amount of internal energy. In a thermodynamic system, the enthalpy is equivalent to the internal energy if the volume and pressure remain constant. Specific enthalpy on the other hand is the enthalpy of one kilogram of any substance. (Infelta 2004 & Heat and thermodynamics 2003) Work: The force applied multiplied by the distance provides for the amount of work done. In a thermodynamic system work done is equivalent to the product of pressure and the change in volume that occurs in the system. It is expressed as W = p ⋅ ΔV Heat: In a thermodynamic system, the change in the internal energy of the system when work is not performed is referred to as heat. In this system, if work is being done, then the internal energy change is calculated by adding the heat as well as the work. Temperature: The extent to which a body is hot or cold is known as the temperature of that body. In a thermodynamic system, when two substances alter each other’s temperature, they actually posses a thermal contact which leads to the heat transfer. Heat moves from the hot body towards the colder one. This process of heat transfer goes on until a state is reached when both the substances have the same temperature and it is referred to as a state of thermal equilibrium. Entropy: When a reversible ideal process, with a steady temperature exchanges heat with the surroundings, this heat change is referred to as entropy. The entropy of 1 kilogram of a substance is referred to as specific entropy. With increased entropy, the amount of work that is done decreases for a fixed amount of enthalpy. (Kondepudi 2008, Infelta 2004 & Heat and thermodynamics 2003) PROPERTIES OF PURE SUBSTANCES Pure Substance: “A pure substance is one that is homogenous and invariable in chemical aggregate. It may exist in one or more phases, but, the chemical composition remains the same in all phases.” (Arora 1998) Thus a substance which has a constant chemical composition is referred to as a pure substance. Water is a pure substance which can also exist as a pure substance in all three states because its chemical composition remains the same. A mixture of water and ice will also remain a pure substance. On the other hand air is a pure substance when it is in the gaseous state because the air is a homogenous mixture. On the other hand liquefied air is not a pure substance because at a constant pressure, the condensation of the constituent elements of liquefied air occurs at different temperatures (Properties of pure substances 2005, Naraghi 1998 & Arora 1998) Phases of pure substances: A phase is the state of the substance in which it exists. It defines the state of matter in which there is homogeneity in the molecular organization which can be differentiated from other phases. The three main phases are solid, liquid and gases. Solid: it is the phase in which the molecules are found at fixed positions and provide a three dimensional view. The molecules can only move at their fixed positions. This indicates the fact that the bonding in this phase is strong as compared to the other phases. Liquid: it is the state of matter in which the molecules are not found at fixed positions and can move about. Also the bonding is relatively weaker as compared to solids but the space between the molecules is not much greater than that of the solid phase. Gas: the molecules are found very far from each other and the bonds between the molecules are very weak. They possess greater energy than the solid or liquid molecules and are in continuous motion. They strike against each other as well as the walls of the system in which they lie (Properties of pure substances 2005, Naraghi 1998 & Arora 1998). Phase transformations of pure substances: Temperature and Volume Graph: This diagram above shows the changes observed in the phase of a pure substance when it is heated. it is a temperature versus volume graph. S=solid, L=liquid, G=gas, Po= zero pressure (Properties of pure substances 2005) A system which is kept at pressure 0 and a solid is heated in it till it turns into a gas assists in understanding the different changes in phase that are seen. The diagram above with the piston represents one such system. It shows the phases in sequence which include solid, mixed phase of solid and liquid, compressed liquid which is still not in the state of vaporizing, wet vaporizing phase in which the temperature of the system remains constant until and unless the vaporization of all the liquid is done and the last phase which is the superheated vapor. The graph on the other hand shows certain important properties of the pure substance. The temperature at which the pure substance boils is referred to as the saturation temperature (Tsat) at a fixed pressure. In a similar way at a fixed temperature, the pressure required to bring a pure substance to boil is referred to as the saturation pressure Psat. In the phase transformations, the pressure and the temperature become dependent variables and are hence denoted as Tsat = f (Psat). Another important point that is seen during the phase changes is the point at which the liquid and the vapors’ cannot be distinguished from each other. This point is referred to as the critical point. Another important point which is known as the triple point is defined as the point at which all three states that is solid, liquid and vapor co exist. On the pressure-volumes and temperature-volume graphs, this triple point is indicated by a line which is referred to as the triple line. The table below indicates the critical and the triple point for oxygen as well as water. (Potter 2009 & Properties of pure substances 2005) Critical Point Triple Point P(atm) T (K/◦C) P(atm) T (K/◦C) H2O 218 647.30/(374.14) 0.006 273.17 (0.01) O2 50.136 154.80/(−118.36) 0.0015 54.16/(−219) (Properties of pure substances 2005) Pressure and volume Graph: (Properties of pure substances 2005) The pressure and volume graph shows a very similar appearance as the temperature and volume graph. The only difference that can be seen is that the lines which denote the constant temperature in this graph show a downward trend. On the other hand the lines on the temperature volume graph, the constant pressure moves upwards. Pressure and temperature graph This graph is also referred to as the phase diagram. This is because it shows a clear demarcation between the three phases that is solid liquid and gas. Pure substances follow this trend with water exhibiting a slightly different nature. This is because unlike other pure substances when water is frozen it increases in size and expands. The processes which are required for the transition of state from solid to gas may be either sublimation which directly converts a solid into a gas. The second process involves the conversion of solid into liquid by melting and then the formation of a gas by the process of evaporation (Properties of pure substances 2005, Naraghi 1998 & Arora 1998) (Properties of pure substances 2005) This diagram which is known as a phase diagram shows the existence of all three phases at the point which is known as the triple point. The line of sublimation demarcates the solid state from the vapor form. In a similar way the vaporization line distinguishes the liquid from the vapor and the melting line the solid and the liquid state. If the pressure applied on the pure substance is lower than the pressure at triple point, the solid does not melt into a liquid but rather changes straight into a gas. On the other hand if the pressure applied is higher than the triple point pressure, the longer process ensues with melting of the pure substance to form a liquid first and then the process of evaporation to give gas (Potter 2009, Properties of pure substances 2005 & Naraghi 1998) PHASE EQUILIBRIUM Phase equilibrium is defined as the state in which equilibrium is attained between two or more different phases and the forces acting in opposite directions possess the same rate so that there is no net change in the phases observed. Equilibrium of two phases of a pure substance can be attained at few pressures and temperatures. When equilibrium is attained no changes in pressure and the temperature are noted. This does not mean that there are no processes taking place in the system but rather the rates of the phase changing processes equal each other and hence it can be said that the rate of condensation is equal to the rate of evaporation if the equilibrium occurs between the liquid and the gaseous phase. This rule is also implied only at a fixed volume. That is phase equilibrium is attained if the volume of the system is not altered. (Potter 2009, Kondepudi 2008 & Arora 1998) ENERGY TRANSFER In thermodynamics the main source of energy transfer is heat but changes in mass and phases are also seen. For heat to be transferred from system to another it is necessary for both the systems to have a ‘thermal contact’. There should be differing temperatures of the two systems as well. Radiation: Certain substances possess the capacity of transferring energy in the form of electromagnetic radiation. This transfer involves the movement of heat from this substance to another one and is done mainly via the electromagnetic waves. The process of radiation mainly occurs in gases or in vacuum but is not very effective in solids and liquids. Radiation leads to the transfer of heat which can then be converted to other forms of energy. Conduction: Conduction is a process of heat transfer which occurs with the assistance of molecules. There is no shift of mass in this process and it predominates mainly in solids. It is basically transferred from one molecule to another and occurs in the same body or it can be transmitted from one to another if the two bodies bear contact with each other. The transfer of heat occurs due to the kinetic energy generated by the movement of molecules in fixed positions. Different substances possess different capacities of conducting heat which is known as the thermal conductivity. The table below shows the thermal conductivity of different substances and assists in analyzing the fact that metals possess a higher capacity of heat conduction as compared to other phases (Arora 2008 & Heat and thermodynamics 2003) (Heat and thermodynamics2003) Convection: The process of convection is different from the other two processes because it involves the movement of the transferring substance. It mainly occurs through flowing fluid which carries with itself heat. Hence there is a transfer of mass as well. Convection mainly occurs in fluids and involves the movement of molecules as well as their displacement. Convection can also be further divided into forced convection as well as natural convection. In natural convection as the name implies the movement of the fluid occurs naturally as a result of heat transfer, which leads to the production of a pressure and a density gradient development. In forced convection equipment is used to drive the fluid by creating a pressure gradient (Arora 2008 & Heat and thermodynamics 2003). Heat transfer can hence be deduced by multiplying the rate of the flow of mass by the changes in the energy which take place in the system. This change either is a change of temperature as well as the phase of the substance. In the case when the phase remains unaltered, this rate of the transfer of heat is calculated by multiplying the rate of mass flow with the specific heat capacity and temperature gradient that exists between the point of entry and exit (Arora 2008 & Heat and thermodynamics 2003). LAWS OF THERMODYNAMICS There are two main laws of thermodynamics which underlie the principles of it study. Two important people can be associated with the discovery of these two laws. James Watt basically introduced a machine which was capable of utilizing fuel and generating heat energy which eventually made the machine work. This formed the basis for the first law of thermodynamics. Sadi Carnot on the other hand, explained a major factor that not all heat can be utilized efficient without any losses and in practical machines while work is performed, a certain amount of the heat is always lost to the environment. This formed the principle of the second law of thermodynamics (Vuille et al 2009, Heat and thermodynamics 2003&Enrico 1956). First Law of Thermodynamics: The first law of thermodynamics states the basic principle of energy that is “energy can neither be created nor destroyed it can only be transformed from one form into another.” But in nuclear processes where the energy is equal to the product of mass and the square of the speed of light, it is seen that mass is changed into energy as well. A thermodynamic system operates on the basis of certain factors which include pressure, temperature and volume. When differences and alterations occur in these factors, they lead to the transfer of heat as well as work with the surroundings. The law implies the fact that the energy of a system remains consistent until and unless an external source or way of transfer of energy to the system is present. If the pressure, volume and other parameters of the system remain unaltered there will be no change in energy and hence no net work will be done. Thus this law is basically a form of the law of conservation of energy. Second Law of Thermodynamics: The second law of thermodynamics explains two factors regarding the thermodynamic system and processes. It explains the fact that all the heat used to produce work in a thermodynamic system is not used completely and that some of the heat is lost. It also explains that the transfer of heat occurs from a hot body towards a cold one and cannot occur vice versa through natural means. (Vuille et al 2009,Heat and thermodynamics 2003 & Enrico 1956). CONCLUSION: Thermodynamics is hence a very important concept of physics which is central to improving the work and efficiency of machines. Certain ideas which are important to the understanding of thermodynamics include internal energy, enthalpy, work, heat, temperature and entropy. In a thermodynamic system, the total energy possessed by the system is referred to as its internal energy and enthalpy is defined as the product of pressure and volume added in the amount of internal energy. The force applied multiplied by the distance provides for the amount of work done and the change in the internal energy of the system when work is not performed is referred to as heat. The extent to which a body is hot or cold is known as the temperature of that body. On the other hand, when a reversible ideal process, with a steady temperature exchanges heat with the surroundings, this heat change is referred to as entropy. Pure substances are those substances which have a constant chemical position and they are also important in thermodynamics. There are three phases of matter which include solid, liquid and gas. A point at which two phases exist in equilibrium with no net change is referred to as phase equilibrium. Thermodynamics is based on two major laws which are known as the first and the second law of thermodynamics. The first law upholds the law of conservation of energy and explains that energy can also change forms but it cannot be made or destructed. The second law explains the fact that heat always moves from a body of higher temperature to a one with lower temperature and does not move in the opposite direction through natural means. Also all the heat energy is not converted into effective work and some of the heat is lost to the atmosphere. The transfer of heat occurs by three important methods which include radiation, conduction and convection. Radiation is most important for gases whereas conduction and convection for solids and liquids respectively. The process of radiation involves the heat transfer by means of electromagnetic radiation whereas conduction occurs via thermal contact and generation of heat from one molecule to another. Convection occurs by means of the motion of the fluid. Works Cited Top of Form Arora, C P. Thermodynamics. New Delhi: Tata McGraw-Hill Pub, 1998. Print. Bottom of Form Fermi, Enrico. Thermodynamics. New York: Dover Publications, 1956. Print. Heat and thermodynamics. (2003) Retrieved from http://canteach.candu.org/library/20030901.pdf Top of Form Infelta, Pierre. Introductory Thermodynamics. Parkland, Fla: Brown Walker Press, 2004. Print. Top of Form Kondepudi, D K. Introduction to Modern Thermodynamics. Chichester, England: Wiley, 2008. Print. Bottom of Form Naraghi, M. Chapter 2: Pure Substances.(1998) Retrieved from http://home.manhattan.edu/~mohammad.naraghi//engs205/chap2.pdf Top of Form Potter, Merle C. Thermodynamics Demystified. New York: McGraw-Hill, 2009. Print. Bottom of Form Bottom of Form Properties of pure substances. University of Waterloo.2005 Retrieved from http://www.mhtlab.uwaterloo.ca/courses/ece309/lectures/pdffiles/summary_ch2.pdf Top of Form Vuille, Chris, Raymond A. Serway, and Jerry S. Faughn.College Physics. Pacific Grove, Calif: Brooks/Cole, 2009. Print. Bottom of Form Read More