Entropy in Our Lives

Entropy

Indeed, entropy governs life. One can view entropy from two different perspectives. One, that it is essentially dispersive in nature. The second is that it is constructive in nature. Entropy is the measure of the spontaneous dispersal of energy within a system or between systems. Chemically, entropy is represented by the symbol, S.

The term entropy has often been misused. It has been misidentified solely as the measure of disorder or chaos. For example, a disorganized room or a pack of cards randomly arranged in a disordered manner is said to have higher entropy. But since there is no change in energy in those systems (through dispersal) it cannot be considered as entropy. (Lambert, 2003)

Entropy can be more explained using the basic laws of thermodynamics from physical chemistry and physics. Indeed, it is these laws that govern nature. The First Law of Thermodynamics states that the energy of the universe remains constant; or, that energy can neither be created nor destroyed. The Second Law of Thermodynamics states that energy dispersal is always spontaneous or that the entropy of natural processes if always positive. This means that in a chemical reaction the dispersed energy of products is greater than that of the reactants. Therefore, the change in entropy, ?S = Sproducts - Sreactants, and ?S > 0. (Atkins and De Paula, 2002)

Entropy effects are seen in almost every instance of life. At an atomic and molecular level, the energy of substances is associated with their motion. A more energetic compound has greater motion. This atomic and molecular motion can be translational, vibrational and/or rotational, in decreasing order of energy. Each of these motions is associated with energy levels that are discrete. Atoms and, in turn, molecules cannot have randomly assigned energies. This means that substances can possess only discrete quanta or packets of energy. Even at a standstill, i.e., at absolute zero of temperature, atoms possess a vibrational energy of 1/2 h?. This is the zero point energy. Here h is Planck's constant and ? is the frequency of vibration.

The entropic dispersal of molecules of perfume in a room of still air is due to the mixing of energy levels of the air molecules and that of perfume. A ball rolling down hill is an example of entropic behavior. The potential energy possessed by the ball is dispersed into heat energy due to friction between the ball and the sloped surface, the kinetic energy of motion and sound energy (among others). The same can be said for a glass of hot water in a colder environment. The dispersal of energy goes from the more energetic glass to the less energetic surroundings. Similarly, if a glass of cold water is placed in warmer surroundings, the heat travels from the warmer surroundings to the cold water.

Spontaneous entropy as defined by the Second Law of Motion is that it tends to disperse energy by increasing the motion of atoms and molecules. Left unchecked, no constituent substance would maintain its integrity. Every atom and molecule would tend to disperse. The word 'tends' is critical here. Systems of checks and balances do not allow unrestricted dispersal to occur. The restrictions are due to internal energies associated with chemical bonds that are fairly high (electrostatic or organic bonds). Water passing through a human body prevents it from spontaneously dispersing. The same is with the difficulty in the combustion of wet and dense wood as opposed to dried leaves and twigs.

In understanding this one must recognize the concept of activation energy. (Clymer, 2002) This is a barrier to spontaneous conversion of reactants to products. Temperature, concentration and the use of catalysts often lower the activation energy. For example, a mixture of hydrogen and oxygen, even in 2:1 molar proportions will not form water spontaneously. The activation barrier has to be overcome by means of a spark, which causes an explosive reaction, thus forming water. A barrier to spontaneous energy dispersal does not mean that the law of entropy is defeated. Both laws of nature are sacrosanct.

To prove this, one might consider the phenomenon of photosynthesis. The leaf captures a very minute percentage of the sun's energy. This energy is dispersed throughout the leaf where food is prepared using carbon dioxide releasing water and oxygen. Some of the energy is also used to build food molecules (chloroplasts). This reconstituting of energy is against the law of spontaneous dispersal. This does not however, defeat the entropy laws. Photosynthesis is a naturally occurring process. Which means the overall entropy change should be positive. In photosynthesis, the overall energy dispersed is more than twice that which is used in recreating food molecules.

Another similar example can be seen in the workings of the mammalian body. The energy supplied from the outside in the form of food combined with the air we breathe is then converted into energy. This concentrated form of energy is dispersed throughout the body, the circulatory system and governed by the central nervous system. This energy dispersal and the processes of metabolism allow our bodies to remain at a constant temperature. Entropy is therefore governed by an energy gradient and dispersed from a high-energy point to a low energy point. This is necessary as is the spontaneity. Consider if the flow of energy was reversed and energy flowed from a lower to higher gradient with negative entropy changes. The move towards equilibrium would be defeated and life would cease to exist.