Thermodynamics Basics

Thermodynamic Processes

• A process is a change from one thermodynamic state to another, defined by parameters like pressure and temperature.
• A thermodynamic state is characterized by independent intensive properties, with two defining the state of a pure substance.

System Boundaries

• The boundary of a system separates it from the surroundings.

Control Volumes and Masses

• A closed system does not exchange mass with its surroundings, whereas a control volume can.
• A control surface can be permeable or impermeable.
• A closed system and control mass are synonymous.

Thermodynamic Properties

• For a pure substance, two independent intensive properties define the state.
• In a given state, all intensive properties have a definite value.
• Thermal energy involves molecular motion and flows from a hotter object to a cooler one.
• Thermal equilibrium means no net thermal energy flow.

Temperature and Energy

• Absolute zero is 0 K, equivalent to -273.15 °C.
• Thermal internal energy is an extensive property, while specific thermal energy is an intensive property.

Gas Laws

• Gas pressure is caused by molecules impacting the walls of their container.
• Charles's law applies to gases at constant temperature, while Boyle's law applies at constant pressure.

Processes and Properties

• An isobaric process occurs at constant pressure.
• A polytropic process includes several types of gas processes as special cases.
• Enthalpy includes internal energy and the product of pressure and volume, and can be greater than internal energy.
• Specific enthalpy is given by h = u + P v.

Thermodynamic Efficiency

• The efficiency of a Carnot engine depends only on the temperatures of the thermal reservoirs.
• Energy and entropy are different properties and are not numerically equal.

Entropy

• During any process, the total entropy of the universe increases (Second Law of Thermodynamics).
• Irreversibilities usually lead to an increase in entropy.
• A real process leads to an increase in the total entropy of the system and its surroundings.