8 th Grade Science Adapted by T. Trimpe sciencespot/

1. Chemical Reactions and Equations 8th Grade Science Adapted by T. Trimpe http://sciencespot.net/ http://www.unit5.org/chemistry/Equations.html

2. Remember: Chemical Changes • Chemical change: a change that occurs causing the identity of the substance to change • Burning paper • Digesting food • Electrolysis of water • A chemical change is called a chemical reaction

3. Remember: Chemical Reaction • Chemical reaction: occurs when the original substance changes form into a new substance. Some clues to a chemical reaction may include bubbles, smoke, a strong smell, color change, temperature change, or a sizzling sound

4. Chemical Changes Cont’d • Indicators of a chemical change: • Evolution of light • Evolution of heat • Evolution of a gas • Color change • Formation of a precipitate

5. Chemical Equations • Depict the kind of reactants and products • and their relative amounts in a reaction. • 4 Al(s) + 3 O2(g) 2 Al2O3(s) • The letters (s), (g), and (l) are the • physical states of compounds

6. Chemical Equations • Reactants – the substances that exist before a chemical change (or reaction) takes place. • Products – the new substance(s) that are formed during the chemical changes. • CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS  PRODUCTS

7. Chemical Equations The number in the front is called a coefficient. It tells you how many molecules in a reaction. • coefficient • 4 Al(s) + 3 O2(g) 2 Al2O3(s) • subscript • The number to the right of the symbols is called a subscript. It tells you how many of the same atom.

8. Chemical Equations • When a coefficient is in front of a molecule and a subscript for an atom, you will multiply both numbers in order to determine the number of atoms that will be involved in the chemical reaction. 2 Al2O3 Al = 4O = 6

9. Let’s Practice

10. Let’s Practice Balance Equations

11. Watch the movie and then complete the chart. Two or more elements or compounds combine to make a more complex substance A + B → AB AB → A + B Compounds break down into simpler substances Occurs when one element replaces another one in a compound AB + C → AC + B AB + CD → AC + BD Occurs when different atoms in two different compounds trade places A = Red B = Blue C = Green D = Yellow

12. Identifying Chemical Reactions 2. Use colored pencils to circle the common atoms or compounds in each equation to help you determine the type of reaction it illustrates. Use the code below to classify each reaction. S = Synthesis D = Decomposition SR = Single Replacement DR = Double Replacement ____ P + O2 → P4O10 ____ Mg + O2 → MgO ____ HgO → Hg + O2 ____ Al2O3 → Al + O2 ____ Cl2 + NaBr → NaCl + Br2 ____ H2 + N2 → NH3

13. ____ Na + Br2 → NaBr ____ CuCl2 + H2S → CuS + HCl ____ HgO + Cl2 → HgCl + O2 ____ C + H2 → CH4 ____ KClO3  →   KCl  +  O2  ____ S8 + F2 → SF6 ____ BaCl2   +   Na2 SO4 →     NaCl   +   BaSO4