Explain it with Atoms and Molecules In a chemical equation, like the one below, you will notice that there are regular-sized numbers in front of some of the molecules and small numbers after certain atoms within a molecule. The little number is called the subscript and tells how many of a certain type of atom are in a molecule. The bigger number is called the coefficient and tells how many of a particular type of molecule there are. If there is a coefficient in front of the molecule and a subscript after an atom, multiply the coefficient and the subscript to get the number of atoms. For example, in the products of the chemical reaction there are two water molecules, or 2H 2 O. The coefficient means that there are two molecules of water. The subscript means that each water molecule has two hydrogen atoms. Since each water molecule has 2 hydrogen atoms and there are two water molecules, there must be 4 (2 × 2) hydrogen atoms. If there is no coefficient, then there is one of that molecule. For example, the methane on the reactant side has 1 methane molecule, with 1 carbon atom, and 4 hydrogen atoms.

The next 4 slides are not in your packet. You have the terms in your Cornell notes.

Vocabulary  Physical Change – A change in size, shape, or state of an object, yet does not change the actual object.  Chemical Change – A change from one substance into another with different properties. Evidence includes: changes in color, odor, or energy either received or given off.

Vocabulary  Chemical Reaction – A process of chemical change occurring when compounds change bonds and creating new different substances.  Chemical Equation – the explanation of a chemical reaction using symbols and numbers to show the atoms involved.  Reactants – Substances that exist before a reaction.  Products – Substances that are formed from a reaction.

Understanding Chemical Equations The point of a formula is to sum up and quickly explain a reaction CH 4 + O 2 + O 2  CO 2 + H 2 O + H 2 O Reactants Products

Understanding Chemical Equations CH 4 + O 2 + O 2  CO 2 + H 2 O + H 2 O Reactants Products is the same equation as 1 CH O 2  1 CO H 2 O is the same equation as CH 4 + 2O 2  CO 2 + 2H 2 O

CH 4 + 2O 2  CO 2 + 2H 2 0 Reactant SideAtomProduct Side Carbon Hydrogen Oxygen # =

6) Are atoms created or destroyed in a chemical reaction? How do you know? What does the picture on the right represent? The products “balance” the reactants. # Reactant atoms = # product atoms. They are just arranged differently! Atoms are not created or destroyed. Same number of each type of atom in the products as in the reactants.

7) In a physical change, like changing state from a solid to a liquid, the substance itself doesn’t really change. Explain how is a chemical change different from a physical change? In a chemical change a new substance with different properties is formed, but in a physical change it only changes size, shape, or state.

C 3 H 8 + 5O 2  3 CO H 2 O Reactant SideAtomProduct Side Carbon Hydrogen Oxygen 8) =

# no

 Do Counting Atoms #1-30 (front side only)  Check and correct with a key at the kiosk