The Hydrogen Economy

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled Perpetual Motion.

The media often perpetuate the idea that the so-called hydrogen economy is the solution to all of our energy needs.  Hydrogen is abundant everywhere; in fact there are oceans full of hydrogen in the form of water, just waiting to be extracted, oxidized and used as an endless source of energy, right?

Perpetual Motion

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled The Definition of Entropy.

It is a consequence of conservation of energy and the second law of thermodynamics that it is impossible to build a perpetual motion machine. There are many types of proposed perpetual motion machines.

There is a post that goes into a lot of detail of the various sorts of perpetual motion machines by Kevin T. Kilty, entitled Perpetual Motion.   Rather than go into arcane detail about different types of perpetual motion machines, I think it suffices to refer the interested reader to Kilty's post.

No machine can generate more more energy than put in (first law of thermodyanics, conservation of energy, Noether's theorem).  The first law of thermodynamics states that work can be converted into heat, and heat can be converted into work, but that the sum, the so-called internal energy (E or U) is a conserved quantity.

The Definition of Entropy

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled: The Carnot Cycle.  This post is heavily dependent on the previous post; so I recommend reading it first. 

Let q represent the heat transferred in a process, and qrev represent the heat transferred in a reversible process. Let T be the absolute temperature (in Kelvin).

The sum of  qrev/T for all steps of the process over a full Carnot cycle is equal to zero.  In fact, it is true for any reversible cyclic process.

The Carnot Cycle

This post is part of a series, Nonsense and the Second Law of Thermodynamics.  The previous post is entitled:  Reversible Processes.

In 1824, Nicolas Léonard Sadi Carnot tried to explain how heat could be converted into useful work. He came up with a four-step cycle that is known as the Carnot cycle.

Reversible Processes

This post is part of a series, Nonsense and the Second Law of Thermodynamics.  The previous post is entitled:  Entropy is Not a Measure of Disorder.

To understand the macroscopic thermodynamic definition of entropy,  it is important to understand something called a reversible process.  A reversible process is just what it sounds like: a process that is reversible.

A reversible process should be thought of as an ideal case. In a reversible process, the system is in equilibrium for every infinitesimal step of the process.  Imagine a balloon filled with gas, and imagine that the balloon is perfect, i.e., we need not concern ourselves with the properties of the balloon itself: we care only about the gas inside the balloon and the gas outside the balloon.

At equilibrium, the pressure on each side of the balloon is equal.  If the pressure outside of the balloon is reduced, the balloon expands until the pressures are equal again.  In a reversible process, the balloon is allowed to expand continuously by infinitesimal steps.  The reversible process acts as a  limit to any real process.

Entropy Is Not a Measure of Disorder

This post is part of a series, Nonsense and the Second Law of Thermodynamics.  The previous post is entitled:  What the Second Law Does Say.

Entropy is not a measure of disorder.  Entropy is not a measure of disorder.

To paraphrase Stanford  Professor H.C. Anderson, there are a lot of sentences in the English language that contain the words "entropy" and "disorder," and most of them are wrong.  There are many reputable text books and sources that say that entropy is disorder; nevertheless, entropy is not a measure of disorder.

What the Second Law Does Say

This post is part of a series, Nonsense and the Second Law of Thermodynamics.  The previous post is entitled:  What the Second Law Does Not Say.

There are multiple valid ways to state the second law of thermodynamics.  Some ways of expressing the law do so in terms of macroscopic notions such as heat and temperature.

Other descriptions employ the concept of entropy, which is based upon a statistical approach to thermodynamics. Some alternative macroscopic statements include:

• There can be no process with the sole result of absorbing heat and completely converting it into work.
• It is impossible to convert heat completely into work in a cyclic process.
• It is impossible to carry out a cyclic process using an engine connected to two heat reservoirs that will have as its only effect the transfer of a quantity of heat from the low-temperature reservoir to the high-temperature reservoir.

What the Second Law Does Not Say

This post is part of a series, Nonsense and the Second Law of Thermodynamics.

The Second Law does not say it is impossible for heat to be transferred from a cold body to a hot body.  The second law does not say that "disorder" must increase on the earth or anywhere else.  Life is not a counter-example to the second law; life is an example of the second law in action.

One has to be very careful about applying statistical results to a single molecule or a few molecules and remembering that increasing entropy applies to irreversible changes, not reversible ones. The second law says nothing about disorder. The second law does not prevent evaporative coolers from operating.

The second law does not contradict radiative transfer theory or global warming. The second law does not contradict conservation of energy.  In applying the second law to  cosmology, one should tread cautiously.

Nonsense and the Second Law of Thermodynamics

Introduction

The Second Law of Thermodynamics is, perhaps, the most abused physical law of all time. It may be rivaled for that distinction by the Uncertainty Principle, Relativity, and Hawking Radiation, but I think the Second Law probably wins the contest.

There is a plethora of nonsense disseminated on the web and elsewhere that misrepresents what the law actually says. This series is an attempt to curb some of that nonsense.  Along the way, I hope to make some sense of what the second law of thermodynamics actually does say, as well as addressing some of the nonsense that people believe about it.

Radiative Transfer

If you are following this primer on infrared spectroscopy and global warming you already have some of the basics of radiative transfer.  The previous post in this series develops a simple multi-layer model of the carbon dioxide in the troposphere.  It leaves out many important features but shows conceptually how absorption and emission behave in layers of the troposphere.

The current post is intended to wrap up the topic and touch upon a few issues that were not discussed. It is possible to teach a year-long course in radiative transfer (or even multiple courses); so of course this post does not do the topic justice, but perhaps it provides some basic principles that give the reader a cursory understanding of the topic.

A Three-Layer Model

This post is part of a primer on infrared spectroscopy and global warming. The previous post introduces a two-layer model  and is a necessary prerequisite to understanding this post.  In this post I start with the following assumptions.  There is a source of infrared radiance that has emissivity of 1, i.e., it radiates as a perfect blackbody at a temperature of  288 K.  The radiance from that layer is I₀

There is a layer of air 1000 m thick with 380 ppm carbon dioxide at a temperature of 278 K.  There is another layer of air 1000 m thick with 380 ppm carbon dioxide at 268 K.  All layers are at a constant pressure of one atmosphere.

A Two-Layer Model

This post is part of a primer on infrared spectroscopy and global warming. The previous post discusses the issue of saturation in the 14-micron band of carbon dioxide in a single-layer model.   The post before that discusses Beer's Law, and is a necessary prerequisite to understanding this post.  This post starts to look beyond the single-layer model, by discussing a two-layer model, and beginning a discussion of radiative transfer.

Molecules and Radiation III: Vibration, Dipoles, and Ro-Vibrational Spectra

This post is part of a primer on infrared spectroscopy and global warming. The previous post looked at the vibrational modes of several molecules including HCl and several molecules of atmospheric interest. This post discusses how these modes relate to infrared absorption and uses HCl as an example.

Infrared Radiation, Black-bodies, and Temperature

This post is part of a primer on infrared spectroscopy and global warming. The previous post discusses the nature of  infrared radiation. This post starts the process of looking at the interaction between infrared radiation and matter and discusses black-bodies and the relationship between temperature and infrared radiation.

 

Figure source.

A Primer on Infrared Spectroscopy and Global Warming

Introduction

This post and the posts linked to it through section headers together form a primer on infrared spectroscopy and how it relates to global warming.  The purpose of the primer is not be to convince skeptics that global warming is real, but rather to explain some of the terms and issues being discussed in climate science.  My goal is not to write a super technical explanation of infrared spectroscopy.  That's been done so many times that it is hardly worth doing again.

Rather, my intent is to write something that clearly describes infrared spectroscopy and relates it to global warming that tries to explain some fairly technical concepts in reasonably plain language.  As such there is an inevitable loss of fidelity about some of the fine points of infrared spectroscopy.  Anyone interested in such detail can follow some of the sources that I will provide.  At some point one has to compromise between accessibility and technical accuracy.  I hope that the choices made in this primer are helpful to some people trying to understand this topic.  This post is an outline of the topics addressed in the linked entries.

What is Infrared Radiation (IR)?

Figure source

This first post starts with the basics.  It discusses the electromagnetic spectrum and where infrared radiation fits into it.  It discusses waves and their measures.  It introduces the idea of electric dipole radiation.  It discusses the units of radiation wavelength, frequency. It ends by discussing photons and energy quantization.