2H2O22H2O?Fundamentals of ChemistryDOE-HDBK-1015/1-93CHEMICAL EQUATIONSRev. 0CH-01Page 43Example 3:Na CO + Ca(OH) NaOH + CaCO2 3 2 3Solution 3:There are two Na atoms on the left so start with the Na by writing Na CO + Ca(OH) 2NaOH + CaCO (guideline b).2 3 2 3By adding the 2, the equation is now completely balanced. This equation illustrates thatnot all equations are that hard to balance.Most chemical equations do not indicate a number of important facts about the chemicalreactions they represent. Chemical equations do not necessarily describe the path by which thesubstances reacting are converted to products. The equation would seem to imply that two molecules of hydrogen collide with one moleculeof oxygen, and two molecules of water are produced. The actual mechanism by which thisreaction takes place is much more complicated and involves a series of processes. Chemicalequations do not indicate the rate at which the reaction proceeds, or even whether the reactionwill occur in a finite time. In many cases, reactions will occur only under a particular set ofcircumstances and then only at a definite rate. Chemical equations do not show whether thereaction proceeds to completion or, if incomplete, the extent of reaction. In most cases, thesubstances that react never completely disappear; however, their concentration may beexceedingly small. Reactions that do not go to completion are usually represented in chemicalequations by using double horizontal arrows . In general, a reaction will go to completion onlyif one or more of the products is removed from the field of the reaction. This is oftenaccomplished if one of the products is a gas or is insoluble in the reaction mixture.In the discussion of chemical equations, emphasis is normally placed on the number of atoms ormolecules involved in the reaction. However, chemical equations are very effective inrepresenting chemical reactions on a macroscopic scale. Practical chemical calculations involvevery large numbers of atoms and molecules.
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business