Chemical Reactions What is a chemical reaction? When substances go through a chemical change and form new substances with different properties. What are some examples of chemical reactions? Rusting of iron Souring of milk Burning of paper Cooking an egg

2 Parts of a chemical reaction: Na + Cl  NaCl ________: substances that enter into a reaction Answer: Reactants ________: substances produced by a reaction Answer: Products Example: What are the reactants and products in the rusting of iron? Reactants Iron, water and oxygen Products Rust

How does a chemical reaction occur? An atom will try to get 8 valence electrons by breaking existing bonds and rearranged to form new bonds. A convenient way to express a chemical reaction is by writing a chemical equation: reactants yields product 4Fe + 3O2  2Fe2O3 coefficients

Law of Conservation of Mass Video In a closed system, matter can not be created or destroyed during a chemical reaction (it can only be rearranged). The total mass of the reactants EQUALS the total mass of the products. Law of Conservation of Mass Video Example: 2H2 + O2  2H2O If the total of 5 grams of Hydrogen and Oxygen gases were combined, then ______ of water would be obtained. Answer: 5 grams

Balanced Chemical Reactions A chemical equation must show that atoms are not created or destroyed (Law of Conservation of Mass). Must have the same number of atoms on both sides of the arrow. Is this equation balanced? H2 + O2  H2O 2H2 + O2  2H2O

Balance the following equations by using coefficients (“numbers in front of substances”) a. Ag + S  Ag2S 2Ag + S  Ag2S b. Al + HCl  H2 + AlCl3 2Al + 6HCl  3H2 + 2AlCl3 c. KI  K + I2 2KI  2K + I2 d. K + O2  K2O 4K + O2  2K2O HI!