Thermodynamics (basic terms).pdf for the learners
- 2. The branch of science that deals with the study of different forms of energy and the quantitative relationships between them.
- 3. Objectives By the end of the lecture, the students will be able to: • Define some basic terms in thermodynamics • State three laws of thermodynamics and its limitations • Explain the application of thermodynamic principles to chemical reactions • Solve thermodynamic calculations (isothermal, enthalpy, entropy changes) • State feasibility and prediction of chemical reactions • Derive Gibbs Helmholtz equation • Explain thermodynamics cycles – Diesel cycle, otto cycle, Rankine cycle
- 4. SOME BASIC TERMS 1. SYSTEM A specific portion of matter under study which is isolated from the rest of the universe with a bounding surface is called a system.
- 5. 2. SURROUNDINGS Anything outside the thermodynamic system is called the surroundings. The system is separated from the surroundings by the boundary. The boundary may be either fixed or moving. 3.BOUNDARY The region that separates the system from the surroundings.
- 6. TYPES OF SYSTEMS a. OPEN SYSTEM There may be both matter and energy transfer across the boundary of the system. b. CLOSED SYSTEM There is no mass transfer across the system boundary. Energy transfer may be there.
- 7. C. ISOLATED SYSTEM There is neither matter nor energy transfer across the boundary of the system. 4. HOMOGENOUS SYSTEM A single phase system is said to be homogenous system as it is uniform throughout. e,g: metallic solids, ice, solution of salt in water, miscible liquid mixtures.
- 8. 5. HETEROGENOUS SYSTEM A system which consists of two phases is said to be a heterogeneous system as it is not uniform throughout. e,g: mixture of two immiscible liquids, mixture of two solids.
- 9. 6. STATE OF THE SYSTEM AND STATE VARIABLE A set of variables such as pressure, volume, temperature, composition, etc. which describes the system is known as the ‘State of the system.’ Thus, when one or more variables under go change, then the system is said to have undergone a change of state.
- 10. 7. STATE FUNCTION The thermodynamic parameters which depend only upon the initial state and final state of the system and does not depend on the path by which the change has been brought about. e.g. internal energy(E), free energy(G), pressure (P), temperature(T) etc.
- 11. 8. PATH FUNCTION It is the sequence of steps starting from the initial to the final state of a system. 9. MACROSCOPIC SYSTEM AND ITS PROPERTIES If a system contains a large number of chemical species such as atoms, ions, and molecules, it is called a macroscopic system.
- 12. a. EXTENSIVE PROPERTIES These properties depend upon the quantity of matter contained in the system. e,g: mass, volume, heat capacity, internal energy, enthalpy, entropy, Gibb's free energy.
- 13. b. INTENSIVE PROPERTIES These properties depend only upon the nature of the substance present and are independent of the amount of the substance present in the system. e,g: temperature, refractive index, density, surface tension, specific heat, freezing point, electromotive force, chemical potential and boiling point.
- 14. 10. TYPES OF THERMODYNAMIC PROCESSES We say that a thermodynamic process has occurred when the system changes from one state (initial) to another state (final). i. IRREVERSIBLE PROCESS If a process is carried out rapidly so that the system does not get a chance to attain equilibrium is said to be an irreversible process.
- 15. ii. REVERSIBLE PROCESS A process which is carried out infinitesimally slowly so that all changes occurring in the direct process can be exactly reversed and the system remains almost in a state of equilibrium with the surroundings at every stage of the process.
- 16. a. Isothermal Process When the temperature of a system remains constant during a process, we call it isothermal. Heat may flow in or out of the system during an isothermal process. b. Adiabatic Process No heat can flow from the system to the surroundings or vice versa.
- 17. c. Isochoric Process It is a process during which the volume of the system is kept constant during each step of process. d. Isobaric Process It is a process during which the pressure of the system is kept constant during the period of change.
- 18. e. Cyclic Process A process during which system comes to its initial state through a number of different processes is called a cyclic or cycle process.
- 19. THERMODYNAMIC EQUILIBRIUM A system is said to be in thermodynamic equilibrium if the macroscopic properties of the system in various phases present in the system do not undergo any change with time. It can be of three types.
- 20. a. Chemical Equilibrium: If the composition of the various phases of the system does not change with time. b. Thermal Equilibrium: If there is no flow of heat from one portion of the system to another part of the system. c. Mechanical Equilibrium: If no mechanical work is done by one part of the system on another part of the system.
- 21. Energetics 1. An exergonic reaction is one in which there is a net energy yield i.e. energy is released (sometimes as chemical bond energy or sometimes as heat). 2. An endergonic reaction is one in which there is a net energy input i.e. energy is needed to drive the reaction (again, sometimes as chemical bond energy and sometimes as heat).
- 22. Both types of reaction, however, have a energy barrier which must be overcome to initiate the reaction - this is termed the activation energy of the reaction (abbreviated to Ea). It is the Ea (and not the overall energy change) which determines the rate of reaction.
- 23. To initiate a reaction between two molecules, they must collide and "stick" together. This "sticking" forms an activated intermediate which goes on to form products. This minimum collision energy which causes them to stick is the activation energy.
- 24. If the rate of molecules colliding and sticking is increased, the rate of reaction is increased. The rate of collision can be increased generally in three ways : i. increase the temperature so the molecules are moving at higher speed ii. increase the concentration of molecules so the chance of a collision is increased iii. use a catalyst