Are We Toast?

Or, Do We Have The Time And Wisdom To Protect Our Planet's Climate?

Energy - Biology, Chemistry and Physics

The biological process of photosynthesis is usually taught as the combination of water (H2O) and carbon dioxide (CO2) to produce a simple sugar, or carbohydrate, called glucose (C6H12O6) and oxygen gas (O2); with the process being driven by sunlight. At this point, the biologist borrows from the science of physics and the first law of thermodynamics - the law of "conservation of matter/energy", which simply states that matter (and energy) cannot be created or destroyed, merely altered in form. The biologist can then borrow from the science of chemistry and represent photosynthesis as a chemical equation:

Solar energy + 6CO2 + 6H2O = C6H12O6 + 6O2

Or, stated in words - in the presence of sunlight we add 6 molecules of carbon dioxide (one atom of carbon and 2 atoms of oxygen) and 6 molecules of water (two atoms of hydrogen and one atom of oxygen) to get one molecule of glucose and 6 molecules of oxygen. Note that the equation is "balanced" that is we have exactly the same number of atoms of each of our chemical elements (carbon, hydrogen, and oxygen) on each side of our equation (each side of the"=" sign), and thus we are in accord with the law of conservation of matter.

We can reverse our equation to represent the process of oxidation (the chemical breakdown of carbohydrate in the presence of oxygen), which is precisely the process that takes place when we burn fossil fuels:

C6H12O6 + 6O2 = 6CO2 + 6H2O + Energy

Once again, the law of conservation of matter has not been violated and we have exactly the same number of atoms of each element on both sides of our equation, and in fact the same number of atoms of Carbon, Hydrogen and Oxygen as we started with in the first equation describing photosynthesis. This point is absolutely fundamental to an understanding of our climate crises, the complete oxidation of fossil fuels releases just as much carbon, as carbon dioxide, as was contained in the oxidized fuel (wood, coal, petroleum, or ethanol). So where does the energy come from? Energy from sunlight is required to combine the simple compounds, water and carbon dioxide into a more complicated, or complex, carbohydrate molecule. The energy is contained in the electron "bonds" that hold the glucose molecule together. The breakdown of the bonds between the atoms of the complex carbohydrate into simpler molecules results in the release of energy. Glucose is one of the simplest sugars; sucrose (table sugar) which is derived from sugar cane and sugar beets has 12 carbon atoms in each molecule, while both corn syrup (fructose) and wood/paper (cellulose) are composed of molecules containing 6 carbon atoms. In general, the more complex the chemical structure of the carbohydrate, the more energy the molecule will release during oxidation.

In addition to oxidation, carbohydrate molecules are also broken down in environments where oxygen is lacking (anaerobic). In such environments, microorganisms play a critical role in the production of such end products as methane (CH4) and alcohols such as ethanol (C2H5OH). Methane, from such sources as rotting vegetation in swamps and bogs, rotting garbage in landfills, and manure digesters is a major greenhouse gas and contributor to global climate change.

Fermentation occurs in the presence of yeast, and the process can be generalized as:

Yeast + C6H12O6 = 2C2H5OH + 2CO2 + Energy.

Again we see that energy is released as the sugar (glucose) is reduced to simpler molecules, in this case one molecule of glucose is reduced into two molecules of ethanol and two molecules of carbon dioxide, and that both sides of the equation contain the same number of carbon, hydrogen and oxygen molecules. It is important to note that the process of conversion of sugar to ethanol releases energy, in the form of heat, resulting in a product, ethanol, with less energy than we started with. The amount of energy that a substance contains is called its "energy density" and is another important concept in the understanding of the climate crises.

In the preceding example of fermentation, we have the same number of atoms of carbon, hydrogen and oxygen on both sides of our equation, but the 2 molecules of ethanol plus the 2 molecules of carbon dioxide (C02) contain less energy than the single, more complex molecule that we started with. Thus the process of fermentation illustrates the second law of thermodynamics, a rather difficult concept, which is usually stated as: "The total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value." Entropy is essentially a state of disorder, so the law basically says that if left alone, systems tend to become less organized. Another way of expressing the law is that without an external influence, energy flows from hot to cold - an example being the cooling of a hot cup of coffee, or melting ice cream. "Energy flows down hill" and "there is no such thing as a free lunch" also express the 2nd law of thermodynamics. The third law of thermodynamics is even more difficult to understand, but it basically means that there is no avoiding the first and second laws.

The laws of thermodynamics define the framework, or limits, of mankind's ability to manage our utilization of energy. We cannot make new energy, but merely alter the form of existing energy and matter; secondly, without the input of new energy, and we cannot make new energy, our systems will eventually run down, reaching a state of maximum disorder, and thirdly there is nothing that we can do about it except to develop the wisdom to understand and accommodate the natural laws, political will to do so, and the individual willingness to compromise.


You are here: Home Background Articles Energy - Biology, Chemistry and Physics