Summary: Episode 21: This is a General Chemistry 101 overview for the MCAT. Get ready for more specific and detailed podcasts on a WEEKLY basis. Conservation of Mass The Law of Conservation of Mass state that there are no detectable changes in mass in any chemical reaction. This indicates that there are the same number of atoms of each types present after a chemical reaction as there were before the reaction. A balanced equation shows equal numbers of each type of atom on each side of the equation and is, thereby, consistent with the Law of Conservation of Mass. MCAT Equations (download complete list of MCAT equations) Equations are balanced by placing coefficients in front of the chemical formulas for the substances involved in the reactions. It is possible to predict the products of simple reactions by analogy to known reactions and by use of the periodic table. Among the reactions, there are the followings: One; combustion in oxygen in which an organic compound reacts with oxygen forming carbon dioxide, water and possibly other products depending on the composition of the compound. Two; neutralization reaction in which an acid plus a base react to form water or another neutral compound and a salt. There are precipitation reactions in which one of the products over reaction between two substances in solution is insoluble in the solution. The coefficient in a balanced equation can be interpreted as either the relative number of formula units involved in the reaction or the relative number of moles. Avagadro's Number A mole of any substance is Avogadro's number, which is 6.02 x 1023 of formula units of that substance. The mass of a mole of atoms, molecules or ions is the formula weight expressed in grams. For example, a single molecule of water, H2O, weighs 18 amu, which are atomic mass units. A mole of water weighs 18 grams. The empirical formula, or simplest formula, of a substance expresses the composition in terms of the smallest possible set of whole number subscripts denoting the relative number of atoms. The mole concept can be used to determine the empirical formula of a compound and calculate the quantities involved in chemical reactions. In dealing with reactions between substances and solutions, it is convenient to employ the concept of solution concentration. Molarity Molarity is defined as the number of moles of solute per liter of solution. Molarity serves as a conversion factor for interconverting solution volume and number of moles of solute. Chemical equations and energy We will look specifically at the energy and the first law of thermodynamics. Energy can be measured in terms of the ability to accomplish work or transfer heat. An object may possess potential energy because of its position relative to another object or because of its composition. Thus, chemical energy is potential energy which can be released when the object undergoes a chemical change. An object may possess kinetic energy because if it's relative motion to another object. The first law of thermodynamics also referred to as the law of conservation of energy states that in any change that occurs in nature, the total energy of the universe remains constant. It is often convenient to consider one portion of nature called the system as separate from all the rest called the surroundings. According to the first law of thermodynamics any energy gained by the system in a change must equal the energy lost from the surroundings. Any process in which heat energy is lost to the surroundings is termed "exothermic". On the other hand, when heat energy is absorbed by the system from the surroundings, the process is termed "endothermic". Heat changes occurring at constant pressure are of special interest. The heat gained or lost by the system in a process occurring at constant pressure is termed the enthalpy change, represented by the symbol delta H. This quantity is negative for an exothermic proc
