CHEMICAL BONDINGDOE-HDBK-1015/1-93Fundamentals of ChemistryCH-01Rev. 0Page 32FormingChemicalCompoundsChemistry and all other sciences are based on facts established through experimentation. Ascientific law is a condensed statement of facts which has been discovered by experiment. There are three basic laws that apply to chemical reactions. They are the Law of Conservationof Mass, the Law of Definite Proportions, and the Law of Multiple Proportions. These lawsare described here to help the reader in understanding the reasons elements and compoundsbehave as they do.1.The Law of Conservation of MassThis law states that in a chemical reaction the total mass of the products equalsthe total mass of the reactants. Antoine Lavoisier, a French chemist, discoveredthat when tin reacts with air in a closed vessel, the weight of the vessel and itscontents is the same after the reaction as it was before. Scientists laterdiscovered that whenever energy (heat, light, radiation) is liberated during areaction, a very small change in mass does occur, but this change is insignificantin ordinary chemical reactions.2.The Law of Definite ProportionsThis law states that no matter how a given chemical compound is prepared, italways contains the same elements in the same proportions by mass. JohnDalton, an English physicist, discovered that when various metals are burned oroxidized in air, they always combine in definite proportions by weight. For example, one part by weight of oxygen always combines with 1.52 parts byweight of magnesium or 37.1 parts by weight of tin. This law results from thefact that a compound is formed by the combination of a definite number ofatoms of one element with a definite number of atoms of another.3.The Law of Multiple ProportionsThis law states that if two elements combine to form more than one compound,the masses of one of the elements combining with a fixed mass of the other arein a simple ratio to one another. For example, carbon forms two commoncompounds with oxygen; carbon monoxide and carbon dioxide. With carbonmonoxide (CO), 1.33 grams of oxygen are combined with 1 gram of carbon.With carbon dioxide (CO ), 2.67 grams of oxygen are combined with 1 gram of2carbon. Therefore, the masses of oxygen combining with a fixed mass of carbonare in the ratio 2:1.
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