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General Chemistry Principles, Patterns, and Applications, 2011

General Chemistry Principles, Patterns, and Applications, 2011

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Ca 5(PO 4) 3(OH)(s) + 7H 3PO 4(aq) + 4H 2O(l) → 5Ca(H 2PO 4) 2·H 2O(s)<br />

The equation is now balanced. Even though we have not explicitly balanced the oxygen atoms, there are<br />

45 oxygen atoms on each side.<br />

2. Check your work. Both sides of the equation contain 5 calcium atoms, 7 phosphorus<br />

atoms, 30 hydrogen atoms, <strong>and</strong> 45 oxygen atoms.<br />

Exercise<br />

Fermentation is a biochemical process that enables yeast cells to live in the absence of oxygen. Humans have<br />

exploited it for centuries to produce wine <strong>and</strong> beer <strong>and</strong> make bread rise. In fermentation, sugars such as<br />

glucose are converted to ethanol <strong>and</strong> carbon dioxide. Write a balanced chemical reaction for the fermentation<br />

of glucose.<br />

Answer: C 6H 12O 6(s) → 2C 2H 5OH(l) + 2CO 2(g)<br />

Summary<br />

In a chemical reaction, one or more substances are transformed to new substances. A chemical reaction is<br />

described by a chemical equation, an expression that gives the identities <strong>and</strong> quantities of the<br />

substances involved in a reaction. A chemical equation shows the starting compound(s)—the reactants—<br />

on the left <strong>and</strong> the final compound(s)—the products—on the right, separated by an arrow. In a balanced<br />

chemical equation, the numbers of atoms of each element <strong>and</strong> the total charge are the same on both sides<br />

of the equation. The number of atoms, molecules, or formula units of a reactant or product in a balanced<br />

chemical equation is the coefficient of that species. The mole ratio of two substances in a chemical<br />

reaction is the ratio of their coefficients in the balanced chemical equation.<br />

K E Y T A K E A W A Y<br />

<br />

A chemical reaction is described by a chemical equation that gives the identities <strong>and</strong> quantities of the<br />

reactants <strong>and</strong> the products.<br />

C O N C E PTUAL P R OBLEMS<br />

1. How does a balanced chemical equation agree with the law of definite proportions?<br />

2. What is the difference between S 8 <strong>and</strong> 8S? Use this example to explain why subscripts in a formula must not<br />

be changed.<br />

3. What factors determine whether a chemical equation is balanced?<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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