Chemical Equations Vocabulary chemical equation reactant product Law of Conservation of Mass coefficient

What do you need to make water? You need hydrogen and oxygen! Are hydrogen and oxygen diatomic elements? Yes! This is a chemical equation H2 + O2  H2O products reactants

Question H2 + O2  H2O products reactants Do you see any problems with the equation below? Where did the oxygen go? H2 + O2  H2O products reactants

Question H2 + O2  H2O products reactants This violates the Law of Conservation of Mass (Matter): Matter cannot be created or destroyed, only rearranged. Where did the oxygen go? H2 + O2  H2O products reactants

What happens to this oxygen? Question Let’s do some accounting: H2 + O2  H2O H O H O H O What happens to this oxygen?

Question H2 + O2  H2O H O H O H O H H O H It reacts with another hydrogen molecule to make another water molecule! H2 + O2  H2O H O H O H O H H O H

Question H2 + O2  H2O H O H O H O H H O H Now how many hydrogen and oxygen atoms are on the left of the equation? On the right? H2 + O2  H2O H O H O H O H H O H

Question 2 H2 + 1 O2  2 H2O H O H O H O H H O H So how many hydrogen molecules do you need? How many oxygen molecules do you need? How many water molecules are created? 2 H2 + 1 O2  2 H2O H O H O coefficient H O H H O H

Question 2 H2 + O2  2 H2O This is called a balanced equation because the number of atoms in the reactants equals the number of atoms in the products.

K2S + F2  2 KF + S 2 K 2 x 1 K 1 S 1 S 2 F 2 F Practice 1 Balance the following K2S + F2  2 KF + S 2 K 2 x 1 K 1 S 1 S 2 F 2 F

2 Al + 3 Cl2  2 AlCl3 2x 1 Al 2x 1 Al 2x 3 Cl 3x 2 Cl Practice 2 Balance the following 2 Al + 3 Cl2  2 AlCl3 2x 1 Al 2x 1 Al 2x 3 Cl 3x 2 Cl

2x 1 Rb 2 Rb 2 NO3 2 NO3 1 Mg 1 Mg 1 S 1 S 2 Rb NO3 ( ) + MgS  Rb2S + Practice 2 Balance the following 2 Rb NO3 ( ) + MgS  Rb2S + Mg(NO3)2 2x 1 Rb 2 Rb 2 NO3 2 NO3 1 Mg 1 Mg 1 S 1 S

2 1 Sr 1 Sr 2x 1 BrO 2 BrO 2 Na 2 Na 1 O 1 O Sr(BrO)2 + Na2O  Na BrO Practice 3 Balance the following 2 Sr(BrO)2 + Na2O  Na BrO ( ) + SrO 1 Sr 1 Sr 2x 1 BrO 2 BrO 2 Na 2 Na 1 O 1 O

2 Al 2x 1 Al 3 C2O4 3x 1 C2O4 2x 3 Cs 6 Cs 2 PO4 2 PO4 ( ) Al2(C2O4)3 Practice 4 Balance the following ( ) Al2(C2O4)3 + 2 Cs3PO4  2 AlPO4 + 3 Cs2 C2O4 2 Al 2x 1 Al 3 C2O4 3x 1 C2O4 2x 3 Cs 6 Cs 2 PO4 2 PO4