In an adiabatic process, there is no heat exchange between the system and its surroundings (Q = 0). For such a process, the first law gives ΔE = W. This means that the internal energy increases if work is done on the system, and this usually leads to a temperature rise. If work is done by the system, the internal …

## UY1: Isothermal Process

In an isothermal process, the temperature of the system is unchanged. (ΔT = 0). For this process, the first law gives ΔE = 0, thus Q = -W. This means that the net heat input into the system equals to the net work output by the system. From the ideal gas equation, P1V1 = P2V2 = nRT (isotherm). Isothermal work done …

## UY1: Concept of heat engines and heat pumps

A heat engine is a device that converts heat into mechanical energy. Conceptualising the heat engine: The heat engine must carry a working substance (usually a gas) through a cyclic process in which the system passes through a series of states. During the cycle:  the working substance absorbs heat (Qh) from a hot reservoir converts part of that heat into …

## UY1: More about internal energy

The internal energy of a system of a system is the microscopic energy associated with the particles in the system. This includes the translational, rotational, vibrational energy of these particles, the inter-particle potential energy, as well as the energy of their electrons and their nuclei. – It does not include the macroscopic kinetic energy associated with the translation or rotation …

## UY1: Definition of first law of thermodynamics

The increase in internal energy of the system is the sum of heat and work input into the system. Differential form of first law of thermodynamics: $$dE = \delta Q + \delta W$$ Integral form of first law of thermodynamics: $$\Delta E = Q + W$$ ,where Q is the net heat input, W is the net work output (mechanical, …

## UY1: Cyclic processes

Although both heat and work involved in the transformation of a system from one state to another is path-dependent, the quantity “Q + W” is experimentally found to be path-independent. In other words, Q + W depends only on the initial and final states of the system! For a cyclic process (i.e., a process that starts and returns to the …

## UY1: Reversible & Irreversible Thermodynamic Processes

Reversible Thermodynamic Processes A reversible transformation is an idealised transformation in which the system is in (very nearly) thermodynamic equilibrium throughout the transformation. – Therefore the system has well-defined values for all its state variables throughout the transformation. – The transformation can be plotted and thus followed on a diagram of state variables. – The system can return to its …