Notes Key Points About All Chemical Reactions:  A new substance is formed NN o atoms are lost or gained during chemical reactions  atomic bonds are broken and new bonds are formed  all chemical reactions produce compounds SPI Law of Conservation of Mass  You start with reactants…you end up with products So no mass is ever lost or gained This is called the Law of Conservation of Mass Press the Right Arrow Button to Advance through the Presentation!

2 parts of chemical equations Reactants: chemicals you start with in a reaction Products: chemicals you end up with in a reaction Example: 2H 2 + O 2 2H 2 O SPI Law of Conservation of Mass Notes Reactants (Hydrogen & Oxygen) Product (water) (1) reactants (2) products

3 key symbols in chemical equations Subscript: small number below & to the right of a chemical symbol  reveals the number of atoms Coefficient: big number in front of a chemical symbol or formula  (tells you to multiply) Yields Arrow: points towards the products Example: 2H 2 + O 2 2H 2 O Notes (1) Subscript (2) Coefficient (3) Yields Arrow SPI Law of Conservation of Mass

Chemical Equations must obey the… … LAW OF CONSERVATION OF MASS!  Atoms are never lost or gained in a chemical reaction … they are just rearranged. Example: Look at the unbalanced equation shown below. It DOES NOT obey the law of conservation of mass. (count the atoms on each side) H 2 + O 2 H 2 O Notes 2 & 1 2 & 2 Four is not equal to three! SPI Law of Conservation of Mass

Balancing Equations: Make the amount of reactants equal the amount of products.  Use coefficients to do this Example: Here is the same equation used on the previous slide, but now I have balanced it by placing coefficients (count the atoms on each side) 2H 2 + O 2 2H 2 O Notes SPI Law of Conservation of Mass 4 & 2 Six is equal to Six! This demonstrates the law of conservation of mass.

Na + Cl 2 2NaCl How many sodium (Na) reactants? How many sodium (Na) products? How many chlorine (Cl) reactants? How many chlorine (Cl) products? Does this demonstrate the law of conservation of mass? Two Quick Review Two No it does not! SPI Law of Conservation of Mass (count the atoms on each side) One Why? Look at the sodium atoms on each side

2N 2 + O 2 2N 2 O How many nitrogen (N) reactants? How many nitrogen (N) products? How many oxygen (O) reactants? How many oxygen (O) products? Does this demonstrate the law of conservation of mass? Four Quick Review Two Yes it does! SPI Law of Conservation of Mass (count the atoms on each side) Four Why? Same number of atoms on each side