Thermodynamics PDF Notes, Important Questions And Synopsis
Thermodynamics PDF Notes, Important Questions and Synopsis
- Thermodynamics deals with the exchange of heat between a body and the surrounding along with other processes accompanying it.
- The nature of heat and its relationship to mechanical work was studied by Joule.
- Thermal equilibrium implies that systems are at the same temperature.
- Internal energy of a system is the sum of kinetic energies and potential energies of the molecular constituents of the system. It does not include the overall kinetic energy of the system.
- Equilibrium states of a thermodynamic system are described by state variables. The value of a state variable depends only on the particular state and not on the path used to arrive at that state.
- Examples of state variables are pressure (P), volume (V), temperature (T) and mass (m). Heat and work are not state variables.
- Zeroth law of thermodynamics: Two systems in thermal equilibrium with a third system are in thermal equilibrium with each other.
- The first law of thermodynamics is based on the principle of conservation of energy.
∆U = ∆Q − P∆V
- Efficiency of a heat engine is the ratio of work done by the engine to input heat.
- If all the input heat is converted entirely to heat, then the engine would have an efficiency of 1.
- In a reversible process, both the system and its environment can be returned to their initial states.
- Spontaneous processes of nature are irreversible. The idealised reversible process is a quasi-static process with no dissipative factors such as friction, viscosity etc.
- A quasi-static process is an infinitely slow process such that the system remains in thermal and mechanical equilibrium with the surroundings throughout. In a quasi-static process, the pressure and temperature of the environment can differ from those of the system only infinitesimally.
- A heat engine is a device in which a system undergoes a cyclic process resulting in conversion of heat to work.
- The Carnot engine is a reversible engine operating between two temperatures T1 (source) and T2 (sink). The Carnot cycle consists of two isothermal processes connected by two adiabatic processes.
- The efficiency of the Carnot engine is independent of the working substance of the engine. It only depends on the temperatures of the hot and cold reservoirs.
- Efficiency of the Carnot engine is 𝜂 = 1 − TC/TH = 1 − (Temperature of cold reservoir/Temperature of hot reservoir).
- The efficiency of an engine is never more than that of a Carnot engine.
- Heat lost by a hot body = heat gained by a cold body
- Heat can flow from cooler surroundings into a hotter body (e.g. coffee) to make it hotter.
No heat engine can convert heat to work with 100% efficiency.
When Q < 0, heat is removed from the system.
When W > 0, work is done by the system.
When W < 0, work is done on the system.
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