Thermodynamics Basics

12 Questions

What is the unit of temperature at which absolute zero is defined?

Kelvin (K)

Which of the following statements is true about Charles's law?

It applies to gases at constant pressure

What is the characteristic of specific thermal energy?

It is an intensive property

Which of the following processes involves no heat transfer?

Adiabatic process

What is the expression for specific enthalpy?

h = u + Pv

Which of the following statements is true about a Carnot engine?

Its efficiency depends on the temperatures of the thermal reservoirs

What separates a system from its surroundings?

A boundary

What is the minimum number of independent intensive properties required to define the state of a pure substance?

Two

Which of the following statements about thermal energy is true?

Thermal energy involves molecular motion

What is the temperature of absolute zero in degrees Celsius?

-273.15 °C

What is the characteristic of a closed system?

It cannot exchange mass with its surroundings

What is the nature of all real processes?

Irreversible

Study Notes

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.