Thermodynamics Systems Overview

The branch of physics that studies heat, temperature, and their relationships to other forms of energy.

Two systems are in thermal equilibrium when they no longer exchange heat between each other. This means their temperatures are the same.

If two systems are in thermal equilibrium with a third system, they are also in thermal equilibrium with each other. This allows us to measure temperature using a thermometer.

The energy associated with the random, disordered motion of molecules within a system.

A group of objects that can exchange energy with its surroundings. It can be a single object or a collection of objects.

A system that allows both energy and matter to be exchanged with its surroundings.

A system that allows only energy transfer with its surroundings, but not matter.

A system that is completely isolated from its environment, preventing any exchange of energy or matter.

Any process that changes the thermodynamic state of a system.

The energy transferred between a system and its environment due to a temperature difference.

The energy associated with the random motion of molecules within a system.

The energy associated with the position or configuration of molecules within a system.

The change in a system's internal energy can happen through two ways: by adding heat or doing work on it.

The force per unit area exerted by a gas on the walls of its container.

Work done by the gas when it expands against an external pressure.

Work done on the gas when it is compressed by an external force.

The energy transferred between systems when a force causes displacement.

A system is in chemical equilibrium when its chemical composition is the same throughout and does not change with time.

The mathematical relation between the state variables is called the equation of state.

For an ideal gas, the equation of state is the ideal gas equation, PV = nRT, where P is pressure, V is volume, T is temperature, n is the number of moles, and R is the gas constant.

The graphical representation of the equation of state of a system, typically a gas, is called the P-V diagram, P-V curve, or indicator diagram.

The area under the curve in the P-V diagram represents the work done in changing the volume of the gas.

When the volume of the gas changes from V1 to V2 at a constant pressure, the curve in the P-V diagram is a line parallel to the volume axis, indicating the work done during the change.

A hypothetical thermodynamic cycle is shown in the figure.

The work done by a gas on a piston when the volume of the gas decreases. The energy is transferred from the gas to the piston, resulting in a negative value for work.

A measurable or observable characteristic of a system in equilibrium. Examples include pressure, temperature, volume, and density.

Variables that do not depend on the size of the system. Think of them as 'qualities' of the substance.

Variables whose values depend on the mass or size of the system. Think of them as 'amounts' of something.

A system where there's no net change in pressure, chemical composition, or temperature. It's in a stable 'balance'.

This state exists when there are no unbalanced forces within or outside the system, resulting in uniform pressure throughout.

A thermodynamic process is any change in the state of a system, involving energy transfer as heat or work.

Work done during a thermodynamic process depends on the specific path taken, not just the initial and final states.

A quasi-static process is a change in a system that occurs extremely slowly, allowing the system to remain in equilibrium at every step.

Heat is transferred into a system when its temperature increases, and transferred out when its temperature decreases.

The amount of heat required to change the volume of the system at constant temperature depends on the thermodynamic process. It's not always the same.

Work done by a system is positive; work done on a system is negative.

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