1. Chemical Reactions - Describing Chemical Reactions Describing Chemical Reactions Cellular phone messages make use of symbols and abbreviations to express ideas in shorter form. Similarly, chemists often use chemical equations in place of words.

2. Chemical Reactions - Describing Chemical Reactions What Are Chemical Equations? Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

3. Chemical Reactions - Describing Chemical Reactions Chemical Formulas The formula of a compound identifies the elements in the compound and the ratios in which their atoms are present.

4. Chemical Reactions - Describing Chemical Reactions Conservation of Mass The principle of conservation of mass states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products.

5. Chemical Reactions - Describing Chemical Reactions Balancing Chemical Equations To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation.

6. Chemical Reactions Balancing Equations Activity Click the Active Art button to open a browser window and access Active Art about balancing equations. - Describing Chemical Reactions

7. Chemical Reactions Balancing Chemical Equations Magnesium metal (Mg) reacts with oxygen gas (O 2 ), forming magnesium oxide (MgO). To write a balanced equation for this reaction, first write the equation using the formulas of the reactants and products, then count the number of atoms of each element. - Describing Chemical Reactions

8. Chemical Reactions Balancing Chemical Equations Balancing Chemical Equations: Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O 2 ), forming sodium oxide (Na 2 O). - Describing Chemical Reactions

9. Chemical Reactions Balancing Chemical Equations Balancing Chemical Equations: Balance the equation for the reaction of tin (Sn) with chlorine gas (Cl 2 ), forming tin chloride (SnCl 2 ). - Describing Chemical Reactions

10. Chemical Reactions Remember These? - Describing Chemical Reactions Key Terms:Examples: Chemical Equation A chemical equation is a short, easy way to show a chemical reaction. reactant A substance you have at the beginning of a reaction is a reactant. product A new substance produced in a reaction is a product. conservation of mass Conservation of mass means that during a chemical reaction, matter is not created or destroyed. A coefficient is a number in a chemical equation telling you how many atoms or molecules of a reactant or product take part in the reaction. Coefficient arrow Chemical Formula subscript