THERMODYNAMICS
Frequently Asked Questions
Thermodynamics is the branch of physics that deals with heat, work, energy, and the laws governing their interconversion in macroscopic systems.
A thermodynamic system is a specified quantity of matter or a region of space chosen for study, separated from its surroundings by a real or imaginary boundary.
The surroundings include everything outside the thermodynamic system that can interact with it by exchanging heat or work.
The thermodynamic state of a system is its condition described completely by state variables such as pressure, volume, and temperature.
State variables are physical quantities whose values depend only on the current state of the system and not on the path followed.
Pressure, volume, temperature, internal energy, entropy, and enthalpy are state variables.
Path variables are quantities whose values depend on the path taken during a process, such as heat and work.
A system is in thermodynamic equilibrium when it is simultaneously in thermal, mechanical, and chemical equilibrium.
An equation of state is a mathematical relation connecting state variables of a system in equilibrium, such as \(PV = nRT\).
An ideal gas is a hypothetical gas whose molecules do not interact except during elastic collisions and obey the ideal gas equation exactly.
The ideal gas equation is \(PV = nRT\), where symbols have their usual meanings.
Internal energy is the total microscopic energy of a system arising from molecular motion and interactions.
The internal energy of an ideal gas depends only on temperature.
The first law states that heat supplied to a system equals the increase in internal energy plus work done by the system.
\(\Delta Q = \Delta U + W\).
Work done is the energy transferred when a force acts through a distance, such as during expansion or compression of a gas.
Heat is energy transferred between a system and surroundings due to a temperature difference.
A quasi-static process proceeds infinitely slowly so that the system remains in equilibrium at every stage.
An isothermal process is one in which temperature remains constant throughout the process.
The system must be in thermal contact with a heat reservoir and the process must be slow.
An adiabatic process is one in which no heat is exchanged with the surroundings.
For an adiabatic process, \(\Delta Q = 0\).
An isochoric process is a thermodynamic process in which volume remains constant.
An isobaric process is a process carried out at constant pressure.
Because volume does not change, and work done\ (W = \int P,dV = 0\).
Specific heat capacity is the amount of heat required to raise the temperature of unit mass of a substance by one degree.
Molar heat capacity is the heat required to raise the temperature of one mole of a substance by one kelvin.
\(C_p\) is molar heat capacity at constant pressure and \(C_v\) is molar heat capacity at constant volume.
For an ideal gas, \(C_p - C_v = R\).
The second law states that natural processes have a preferred direction and heat cannot be completely converted into work.
It is impossible to convert all absorbed heat into work in a cyclic process using a single reservoir.
Heat cannot flow from a colder body to a hotter body without external work.
Yes, violation of one implies violation of the other.
A heat engine is a device that converts heat into work while operating in a cycle.
Efficiency is the ratio of work output to heat absorbed from the hot reservoir.
Because some heat must always be rejected to a cold reservoir, as required by the second law.
A refrigerator transfers heat from a colder region to a hotter region by consuming external work.
COP is the ratio of heat extracted from the cold reservoir to work done.
A reversible process can be reversed without leaving any net change in system and surroundings.
An irreversible process cannot be reversed without leaving permanent changes.
No, reversible processes are idealized and do not occur exactly in nature.
Entropy is a measure of disorder or randomness of a system.
Entropy of the universe increases in irreversible processes.
A Carnot engine is an ideal heat engine operating reversibly between two reservoirs.
Carnot efficiency is the maximum possible efficiency between two temperatures.
\(\eta = 1 - \frac{T_C}{T_H}\).
No, it depends only on reservoir temperatures.
It sets the upper limit of efficiency for all real engines.
No, absolute zero cannot be achieved.
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