What Is The Formula For A Volume Of A Cylinder Chemistry and Thermodynamics

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Chemistry and Thermodynamics

Lost in the woods of science.

The study of science starts for everyone as a small trail in the woods of ignorance, but with effort and experience, that trail becomes our personal highway of knowledge and information, opening many possibilities. Albert Einstein, like everyone else, started out in the woods, and he showed that getting out is worth the effort, not just for him, but for all his knowledge did for Mankind. Science is not for everyone and few Einstein’s exist. Sadly many get lost, confused and frustrated, giving up before they can utter their first “Eureka”, as a gem of knowledge falls into place. Those “Eureka” moments can excite us to keep going down our particular path.

So the first step is to be motivated and want to know more.

The next important step is to pay attention to the definitions: something that is important in every area: in sports you must know the rules to play the game: it is same for science. Knowing the definitions clears up confusions, and applying them (solving problems) solidifies them. Eventually the scientific method and thinking become a way of life, and gives insight into many situations, even outside your particular area of expertise.

A structure emerges. For example, the life sciences and medicine rest upon biochemistry and pharmacology, which rests upon organic chemistry, and organic depends on physical chemistry. Physical chemistry rests upon physics, and mathematics is the logic that binds them all together.

Along the way there are many sidelines, too numerous to list here: new materials, nano-technology are two important and well known disciplines. Also various areas overlap into multi-discipline fields, like physical chemistry and organic (physical-organic chemistry); organic synthesis and chemical kinetics (organocatalysis), Inorganic and organic chemistry (organometallic chemistry): the list goes on and on.

Clearly no-one can become an expert in all of these areas. However a good foundation in the basic of physical science allows one to at least be in a position to appreciate the work of others in the many areas of scientific endeavor. You might end up as a lawyer, a social worker or in finance. A good background in science will help the lawyer argue his case of, say, patent violation; helps the social worker understand the side effects of medication a client might be taking, and allows the financier to make intelligent decisions about whether to invest in one mining company or another.

On the other hand, you might become a scientist which leads to many interesting careers.

Scientists and engineers

Science can be divided into two broad categories: fundamental science (research), and applying those ideas (engineering: also called Research and Development (R&D)). Today there are about ten times more engineers than there are scientists. It takes more effort and more people to take the fundamental ideas developed by a few, and turn them into technology that we use to improve our quality of life.

Think of the automobile industry. The internal combustion engine, based upon the Otto cycle was developed by a few (who showed it worked), and then many engineers took that basic idea and over the last hundred years developed the cars we have today.

To be a good engineer, you must start with the fundamentals and learn the basics before you can apply them.

The macroscopic and the microscopic

A broad division of science is into the macroscopic (big enough sample that we can measure and examine), and the microscopic (atoms, molecules and collections of these, too small to observe individually).

There are two big cornerstones of macroscopic science: Thermodynamics (the study of heat, work and efficiency), and Classical Mechanics (Newtonian physics that describes the motion of macroscopic objects).

The microscopic is governed by quantum mechanics.

Since microscopic particles have a lot of symmetry, the field of group theory (a mathematical subject) should be mentioned. This helps to visualize molecules and reactions, and has particular relevance in the most fundamental science, which is physics. You do not have to be a mathematician to use group theory. Mathematics is a tool of scientists: logic guides us.

The field of Statistical Mechanics relates macroscopic objects to its microscopic particles.

The example of chemistry

Chemistry is the study of the making and breaking of bonds-that is chemicals react to form different chemicals. A chemical reaction proceeds if the conditions are right: two important conditions are energy and entropy. Both are substances and entropy is as tangible as energy. How did this come about?

Engineers started to notice things a couple of hundred years ago: like horses that walked in a circle and drove the machinery to bore cannons. The horses walked at a constant rate, (constant energy) but a dull bit produced a lot of heat and not a lot of work (boring the cannon was slow), but a sharp bit produced a lot less heat and more boring. This is the First Law of Thermodynamics:

Energy (horse power) = heat (friction) + work (cannon bore).

Clearly energy is not cheap (the horses must be purchased, fed and cared for), so it would be better to reduce the heat loss and increase the work done. That is, the efficiency of the use of energy became an important consideration.

In the 19th century, thermodynamics further evolved motivated by the need to increase efficiency of the steam engine that drove the industrial revolution. The first steam engines were about 3% efficient and so improvements were definitely needed. Adding a second cylinder, for example, improved things lot but they could do more? Could the dream of 100% efficiency come true-i. e. perpetual motion?

This led Sadi Carnot in the 1830’s to define a cycle for the steam engine from which entropy was discovered, and the Second law of Thermodynamics was formulated-perpetual motion was shown to be impossible. The Otto cycle was developed for an internal combustion engine about forty years later.

Although alchemy is an old subject, it was only after the First and Second Laws of thermodynamics were developed that chemistry really took off. Many were involved in its development. Besides Sadi Carnot, a few notable names are James Maxwell, Rudolf Clausius, James Joule, Willard Gibbs and Ludwig Boltzmann.

The ideas they developed apply well to chemistry. When bonds are broken, energy must be added to the system; and when bonds are formed, energy is released to the surroundings. Some chemical reactions produce more randomness (higher entropy) and sometimes more order (lower entropy) as the atoms rearrange to form products. Both energy (heat and work) and entropy (randomness) play important roles in the spontaneity of a chemical reaction.

Here is an example. Trinitrotoluene (TNT) can explode (a rapid chemical reaction). From the chemical formula it has three nitrogen bonds. Most chemical explosives contain nitrogen by the way. The combustion of one mole of TNT releases 3,400 kJ mol-1 of energy,

C7H5N3O6(s) + 21/4 O2(g) à7 CO2(g) + 5/2 H2O(g) + 3/2 N2 (g) ∆H = -3,400 kJmol-1

Compare this, however, with the energy of combustion of sugar as sucrose (a slow chemical reaction),

C12H22O11(s) + 12 O2(g) à12 CO2(g) + 11 H2O(l) ∆H = -5,644 kJ mol-1

Sucrose produces a lot more energy per mole that TNT! So why is not sucrose an explosive too? Sucrose burns slowly relative to TNT, with a corresponding slow release of carbon dioxide. TNT burns so fast that a lot of energy is released in a short period of time. Furthermore, solid TNT occupies a small volume, but the final volume is equal to 11 moles of gas (about 250 liters at STP). The destruction is not caused so much by the heat released but the rapid expansion of the gases produced. Using the First Law, the energy released by one mole, (3,400 kJ) goes into some heat but a lot of work is done to the surroundings as the gas expands, and this can cause damage.

This is where entropy comes in. Notice that the right hand side of the TNT combustion has only 21/4=5.25 moles of gas, while the RHS has 11 moles of gas. This means there is more disorder on the RHS than the LHS. Clearly the rapid expansion in the explosive combustion of TNT can lead to destruction (it would knock Humpty Dumpty off his wall) and cause greater disorder and therefore the entropy increases. Both energy and entropy are favorable for this reaction to proceed. This is not always the case, especially biological processes, where entropy, not energy, is the main driving force.

Thermodynamics tells us which chemical reactions will proceed and which will not. Chemical Kinetics tells us how fast those reactions take place, and how much energy is needed to initiate a reaction. TNT is not very sensitive to shock because it has a high activation energy. On the other hand, Nitroglycerine, (NG), another chemical explosive (with lots of nitrogen bonds), explodes with a small shock and cannot be transported in liquid form at room temperature. It has a low activation energy. Alfred Nobel solved the nitroglycerine problem by inventing dynamite: reducing the sensitivity to shock by soaking NG in sawdust, paper or some absorptive material. The patent was so successful that he left us the legacy of the Nobel Prize.

Equilibrium thermodynamics is a closed field today with no new fundamental research being done. It is a beautiful, complete and compact theory that gives the relationship between the macroscopic quantities we can measure: energy, heat capacities, compressibility factors and many more, with wide application.

Thermodynamics is essential knowledge for all chemists. However thermodynamics fails to explain why these relationships exist. This is given by another elegant theory called Statistical Mechanics.

Physical Chemistry covers all these.

There is a lot more to say, but that is a summary. Actually many say that thermodynamics is not a good name because it describes equilibrium properties, not dynamical one. A better name would be thermostatics–but nobody calls it that.

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