Biochemical and Biophysical Phenomena 751 



stant). Usually we think of energy as the ability to produce a change 

 or motion in matter (ability to perform work) and matter as anything 

 which occupies space and has weight. Energy may take the form of 

 heat, light, electricity, or motion. Potential energy is the ability to per- 

 form work because of the position (of atoms, molecules, or larger bodies), 

 while kinetic energy is the energy of movement. A stationary ball at 

 the top of an inclined plane has potential energy, but it displays kinetic 

 energy as it rolls (motion) down the incline. Stored energy in foods is 

 potential energy because of the position of atoms in the food molecules, 

 but chemical digestion of the food results in changing the potential 

 energy into heat, light, electricity, or energy of movement. According 

 to the law of the conservation of energy, it cannot be created or destroyed 

 but only transformed into another form. There are many examples of 

 this law in the living and nonliving world. 



All matter, whether it be solid, liquid, or gas, is composed of atoms. 

 The properties of atoms and molecules are considered elsewhere and 

 should be reviewed. 



Electrolytic Dissociation 



Electrolytes (e -lek' tro lite) (Gr. elektron, amber or electricity; lutos., 

 soluble) are substances which in solution are able to conduct electric cur- 

 rents, while those which do not are known as nonelectrolytes. For in- 

 stance, sodium hydroxide (NaOH) in solution has positively charged 

 Na ions and negatively charged OH ions. The Na atom acquires this 

 positive charge because it loses an electron, while the OH atom acquires 

 a negative charge because it gains an electron. Atoms charged in this 

 way are called ions. Compounds which dissociate or ionize in such a 

 manner are electrolytes. In general, inorganic compounds exhibit ioni- 

 zation to a greater extent than organic compounds. Acids, bases, and 

 salts are good electrolytes, while alcohols and sugars are not. Ordinary 

 salt (NaCl) dissociates or ionizes into a positively charged sodium ion 

 (Na+) and a negatively charged chlorine ion (C1-). The base, sodium 

 hydroxide (NaOH), dissociates in water into a positive sodium ion 

 (Na+) and the negative hydroxyl ion (OH-). The hydroxyl ions give 

 the alkaline or basic properties to the solution. In water, hydrochloric 

 acid (HCl) dissociates into positive hydrogen ions (H+) and negative 

 chlorine ions (CI—). The hydrogen ions give the acid properties to an 

 acid. The numbers of hydrogen ions in a solution are an index of its 

 acidity, and the hydrogen-ion concentration is expressed by the symbol 



