It is defined as force per unit area i.e., When heat flows into the system then it is taken as +ve and when heat flows out of the system then it is taken as –ve. If Q is the heat transfer, then the magnitude of heat transfer during the process 1-2 is given by, Like work, heat is a path function and we know that the differentials of path functions are imperfect differentials. At this stage the two bodies will be at the same temperature. When the two bodies, one hot and the other cold are kept in contact with each other, then the hot body loses heat and becomes colder and the cold body gains heat and becomes hotter and this process continues till the thermal equilibrium is reached. “Heat is a form of energy, which crosses the system boundary due to the temperature difference between the system and the surroundings”. Here the piston is assumed to move very slowly so that path 1-2 is Quasi-static (i.e., nearly static) and every state passed through is an equilibrium state. The work done W 1-2 will be equal to the area under the curve 1-2 on the PV-diagram. The initial and final states of the system can be represented on PV- diagram. If a is the cross sectional area in m 2, then the force acting on the piston is given by –Īnd the small amount of work done by the gas on the piston is causing the displacement Now, consider a small movement of the piston dl during which pressure P is assumed to be constant. Then the pressure falls to P 2 and volume will increase to V 2. Let the gas expands as the piston moves to position (2). During the initial condition of the piston i.e., when the piston is at position (1), the pressure inside the cylinder is P 1 and volume is V 1. PdV Work in Various Quasi-Static Processes :Ĭonsider a system consisting of a gas in a cylinder fitted with a piston. Equations for Work Done in Various Processes : Operator δ is used to denote inexact differentials, operator d is used to denote exact differentials.Ģ. The differentials of point functions are exact or perfect differentials and the integration is simply, e.g., During change of states, the values of the properties will change and this change in values of the properties does not depend on path, but it depends upon end states and hence all the properties are point functions. Thermodynamic properties are point functions, since for a given state, there is a definite value for each property. So, work is called Path function and δW is an inexact or imperfect differential. So, the work done during the process directly depends upon the path and not on the end states.
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