Thermodynamics

Card # 27 Thermodynamics Thermodynamics is the study of transfer of thermal energy into mechanical energy. Using this thermodynamic system is studied. A thermodynamics system may be an assembly of large number of particles having a certain value of Pressure (P), Volume (V) and Temperature (T). These are known as thermodynamic variables. Change of State of a thermodynamic system is due to the change in one or more of these variables. Thermodynamic System + Surrounding = Universe Zeroth Law of Thermodynamics Two bodies or systems that are in thermal equilibrium with a third body are in thermal equilibrium with each other. Heat will be exchanged between A and C also between B and C till they reach in thermal equilibrium i.e. If TA = TC and TB = TC then TA = TB First Law of Thermodynamics The First law of thermodynamics is based on the idea that energy is neither created nor destroyed in any thermodynamic system. The heat Q added to the system can cause two changes 1. Increased the internal energy by raising the temperature of the gas. 2. It can cause the gas to expand in means allowing the gas to work. Heat added to the System = Increase in internal Energy of the system Q = ΔU + W

+

External work done by the System

Heat added to the System will be equal to work done Q = W . Limitations of 1st Law of Thermodynamics 1st Law states that the energy remains conserved but it doesn’t indicate 1. The direction of heat transfer. 2. The conditions under which heat can be converted into work. 3. It doesn’t tell why the whole of heat energy cannot be converted into mechanical work. There are many irreversible process occur in nature. 1st law cannot explain the lack of reversibility. Example: Heat flows naturally from a hot body to cold body but heat will never of itself flow from a cold body to a hot body. Second Law of Thermodynamics Kelvin Planck Statement It is not possible to construct a heat engine which can absorb heat from a reservoir and convert the entire heat into work. Clausices Statement It is not possible to transfer heat from a cold body to hot body without the help of some external agency.