Glossary
Adiabatic Process
A thermodynamic process where no heat is exchanged between the system and its surroundings ($Q=0$). For such a process, the change in internal energy is equal to the work done on the system ($\Delta U = W$).
Example:
The rapid expansion of gas from an aerosol can, which causes the can to feel cold, is an adiabatic process because there's insufficient time for heat exchange with the surroundings.
First Law of Thermodynamics
A statement of the conservation of energy, asserting that energy cannot be created or destroyed, only converted from one form to another. It is expressed as $\Delta U = Q + W$, where $\Delta U$ is the change in internal energy, Q is heat added, and W is work done on the system.
Example:
If a gas is compressed (work is done on it) and simultaneously releases heat, the change in its internal energy is precisely accounted for by the First Law of Thermodynamics.
Heat (Thermodynamics)
Energy transferred between systems or a system and its surroundings due to a temperature difference. Positive heat (Q) indicates energy added to the system.
Example:
Placing a hot cup of tea on a cold table causes heat to transfer from the tea to the table until they reach thermal equilibrium.
Internal Energy (ΔU)
The total energy contained within a thermodynamic system, representing the sum of the kinetic and potential energies of its constituent particles. A change in internal energy ($\Delta U$) is directly related to a change in the system's temperature.
Example:
When you rapidly pump up a bicycle tire, the air inside gets warmer because the work done on the gas increases its internal energy.
Isobaric Process
A thermodynamic process that occurs at a constant pressure. On a PV diagram, an isobaric process is represented by a horizontal line.
Example:
Boiling water in an open pot is an isobaric process because the pressure remains constant at atmospheric pressure while the volume of the steam increases.
Isochoric/Isovolumetric Process
A thermodynamic process that occurs at a constant volume. In an isochoric process, no work is done by or on the system, so $\Delta U = Q$. On a PV diagram, it's a vertical line.
Example:
Heating a gas inside a rigid, sealed container, like a pressure cooker, is an isochoric process because the volume of the gas cannot change.
Isothermal Process
A thermodynamic process that occurs at a constant temperature. For an ideal gas, this means the change in internal energy is zero ($\Delta U = 0$), so $Q = -W$.
Example:
A gas expanding very slowly while submerged in a large water bath can approximate an isothermal process, as heat can transfer to keep its temperature constant.
PV Diagram
A graphical representation that plots the pressure (P) of a system against its volume (V). The area under the curve on a PV diagram represents the work done during a thermodynamic process.
Example:
To calculate the net work done by a heat engine over a complete cycle, you would find the area enclosed by the loop on its PV diagram.
Thermal Equilibrium
A state where there is no net flow of heat between two objects or systems in contact, indicating they are at the same temperature. This is a fundamental concept for understanding heat transfer.
Example:
After a cold soda can sits on a counter for several hours, it will eventually reach thermal equilibrium with the room, and its temperature will no longer change.
Work (Thermodynamics)
Energy transferred by a force acting over a distance, specifically in thermodynamics, often related to changes in volume against pressure. In the context of the First Law, positive work is done *on* the system.
Example:
When a gas expands and pushes a piston, the gas is doing work on the piston, which is considered negative work on the system.
Zeroth Law of Thermodynamics
States that if two objects are each in thermal equilibrium with a third object, then they are in thermal equilibrium with each other. It establishes the concept of temperature measurement.
Example:
If a thermometer (object A) reads the same temperature when placed in a beaker of water (object B) and then in a cup of coffee (object C), then the water and coffee are in thermal equilibrium with each other.