Some of the most important Physics Topics include energy, motion, and force.
What are the 4 Thermodynamic Processes?
Thermodynamic equilibrium: The macroscopic properties that are used to describe a system may change spontaneously or due to an external influence. During such a change, the system and its surroundings interact with each other.
i) Absence of unbalanced force or torque in the interior of a system or between a system and its surroundings implies mechanical equilibrium has been established.
ii) For a system in mechanical equilibrium, when there is no spontaneous change of internal structure (by means of chemical reaction) or transfer of matter from one part of the system to another (by means of diffusion) chemical equilibrium is said to be established.
iii) For a system in mechanical and chemical equilibrium, thermal equilibrium is set to be attained if no exchange of heat occurs between the system and its surroundings. Hence it is obvious that in thermal equilibrium, the temperature remains the same throughout the system and is identical with that of the surroundings.
When all the three types of equilibrium stated above are attained by a system, it is said to be in a thermodynamic equilibrium or in an equilibrium state or simply, in a state.
A closed thermodynamic system, i.e., a system having a fixed mass, can be described completely by three of its properties—volume (V), pressure (p) and temperature (T). All other properties of the system depend on these properties and therefore are functions of, V, p and T. In thermodynamic equilibrium none of the three properties ola system— volume, pressure or temperature—changes with time. In our study, we shall deal with equilibrium states and V, p and T will not be treated as functions of time. So, the quantity time will never appear in our formulation of thermodynamic relations.
Moreover, volume, pressure and temperature are related among themselves by an equation of state. Thus, if two of them are known, the third can be calculated using that equation of state. Hence, there are only two independent properties for a closed thermodynamic system. For example, let a fixed mass of 1 mol of a gas be taken at STP. Then,
p = 1 atm = 76 cm of mercury
= 76 × 13.6 × 980 dyn ᐧ cm-2;
T = 0°C = 273K
If the gas is assumed to be ideal, then from the equation of state pV = RT, we have
V = \(\frac{R T}{p}\) = \(\frac{8.31 \times 10^7 \mathrm{erg} \cdot \mathrm{mol}^{-1} \cdot \mathrm{K}^{-1} \times 273 \mathrm{~K}}{76 \times 13.6 \times 980 \mathrm{dyn} \cdot \mathrm{cm}^{-2}}\)
= 22400 cm3 ᐧ mol-1 = 22.4 l ᐧ mol-1
Here p and T played the role of independent properties and V could be calculated from them.
Thermodynamic process: Let a system be initially at an equilibrium state A. Now, if the system exchanges energy, in the form of work or heat, with its surroundings, then the values of V, p and T would change, in general. So, the system would deviate from the state A. But eventually, when the energy exchange stops, the system would attain a new equilibrium state, say B.
The transition of a system from an initial state A to a final state B is known as thermodynamic process and is usually denoted as A → B [Fig.]. It should be noted that, the transition between two states may occur along different paths 1, 2, …… Each of these paths corresponds to a seperate process.
A process, in general, involves simultaneous changes of all the three properties-volume (V), pressure (p) and temperature (T). However, for simplicity of analysis, some special processes are often considered :
- Isochoric process: The volume of a system remains constant in this process. But, both pressure and temperature undergo some changes.
- Isobaric process: Here, p remains constant and V and T change their values.
- Isothermal process : T is a constant, whereas there are changes in V and p.
- Adiabatic process: The heat exchange between the system and its surroundings remains zero; there are changes in all of V, p and T.