Thermodynamics is the branch of physics that deals with energy transformations involving heat and work. It is focused on understanding how energy moves and changes form in physical systems.

The First Law of Thermodynamics embodies the principle of conservation of energy by stating that energy cannot be created or destroyed, only transformed. It provides the foundation for energy balance calculations in thermodynamic processes.

Absolute zero is defined as 0 Kelvin, equivalent to −273.15°C, and represents the lowest possible temperature where particle motion nearly ceases. This concept is fundamental in understanding the limits of thermal energy in a system.

Conduction is the process in which heat is transferred through direct contact between molecules in a substance. This mode of heat transfer is especially significant in solids where molecules are closely packed.

A closed system is defined by its ability to exchange energy with its surroundings while preventing any mass flow. This is a key concept that differentiates it from open systems (exchanging both matter and energy) and isolated systems (exchanging neither).

In an isothermal process, the temperature remains constant, meaning the internal energy of an ideal gas, which depends only on temperature, does not change. Therefore, the change in internal energy is zero.

An adiabatic process is characterized by the absence of heat exchange between the system and its surroundings (Q = 0). Any energy change in the system is solely due to work done by or on the system.

The efficiency of a heat engine is largely determined by the temperature difference between its high-temperature source and low-temperature sink, as outlined by the Carnot principle. A larger temperature difference generally enables higher efficiency.

A Carnot engine is an idealized engine model that achieves maximum efficiency by operating reversibly between two heat reservoirs. Its efficiency is solely determined by the temperatures of these reservoirs, setting an upper limit for all real engines.

The First Law of Thermodynamics is expressed as ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added to the system, and W is the work done by the system. This formulation highlights energy conservation in thermodynamic processes.

At constant pressure, the work done by a gas is simply the product of the pressure and the change in volume. This relationship is a direct consequence of the definition of work in thermodynamics.

Entropy is a state function that quantifies the disorder or randomness of a system. It serves as a measure of energy dispersion and indicates the portion of energy in a system that is not available to perform work.

For a reversible process, the change in entropy (ΔS) is defined as the amount of reversible heat transferred (Q_rev) divided by the temperature (T) at which the transfer occurs. This relationship is fundamental to calculating entropy changes in thermodynamic systems.

Specific heat capacity defines how much heat energy is needed to raise the temperature of a unit mass of a substance by 1°C. It is an intrinsic property that helps determine how a substance responds to heat addition.

Friction converts mechanical energy into thermal energy, resulting in an increase in temperature. This process is commonly observed when surfaces rub together, causing energy dissipation as heat.

The efficiency of a Carnot engine is determined by the formula 1 - (T_cold/T_hot). Substituting the values 300 K and 600 K gives 1 - (300/600) = 0.5, or 50%. This represents the maximum possible efficiency between the two reservoirs.

For an adiabatic process, the relationship PV^γ = constant holds. Doubling the volume causes the pressure to drop by a factor of 2^γ. With γ = 1.4, 2^1.4 is approximately 2.64, meaning the pressure decreases to roughly 1/2.64 (about 38%) of its original value.

When the polytropic index n is equal to the specific heat ratio γ, the process becomes adiabatic. An adiabatic process is one in which no heat is exchanged with the surroundings, aligning with this condition.

According to the First Law of Thermodynamics, ΔU = Q - W. With Q = 500 J and W = 200 J, the change in internal energy is 500 J - 200 J = 300 J. This calculation demonstrates energy conservation within the system.

The Joule-Thomson effect is governed by the relationship between the gas's initial temperature and its inversion temperature. This determines whether the gas cools or heats during a throttling process, making it the most critical factor.