Lesson #5:Chemical Equations

A Chemical Reaction

• A process in which a substance (elements, molecules, ions etc.) reacts with another substance or energy to form a new substance

What are some signs that a chemical reaction is taking place?

• What reacted with what? How much reacted? What is the result of the reaction? How much did we get?

A Chemical Equation

Reactant

Product

The “Recipe” of a chemical reaction

• Describes how much of one substance reacts with one or more other substances to produce an amount of a new substance or substances

2H2 (g) + O2 (g) 2H20 (l)

• A substance (element, ion, molecule) that reacts or is changed during the chemical reaction

• the stuff before the arrow

• A substance that is produced by a chemical reaction

• the end result(s) of a chemical reaction

• the stuff after the arrow

ReactantsProducts

the arrow separates the reactants

from the products in the equation

and means “produces

Subscript

Coefficient

2H2 (g) + O2 (g) 2H20 (l)

• Number that indicates how many atoms of an element are in a compound

• the “little” numbers

• Number that indicates how many molecules of the compound are present in the reaction

• the “big: numbers

Subscripts

Coefficient

The Law of Conservation

of Mass

2H2 (g) + O2 (g) 2H20 (l)

• This equation means that 2 molecules of Hydrogen Gas and 1 molecule of Oxygen Gas react to produce 2 molecules of liquid Dihydrogen Monoxide (commonly known as water)

• Mass cannot be created or destroyed in a chemical reaction

• Every chemical reaction must have equal numbers of atoms of each element on each side of the equation

Why?

Balancing Chemical Equations

• Chemical Equations must obey the Law of Conservation of Mass. Atoms CANNOT be created or destroyed in a chemical reaction.

• This involves “Balancing” a chemical equation

• When Balancing a Chemical Equation we must follow these rules

1. You CANNOT change the formula of any reactant or product in order to balance an equation

- changing the formula means we have changed the substance and the reaction which is bad.

- DON’T TOUCH THE SUBSCRIPTS!

2. You can only change the coefficients in front of the reactants and products

YES 2H2O

NO H22O

Balancing Chemical Equations

• Here are some general steps to balancing a chemical equation

1. Create a Skeleton Equation

- A Skeleton Equation is an unbalanced chemical equation

- The purpose of the skeleton equation is to show the proper chemical formulas for each reactant(s) and product(s) involved in the reaction

2. Balance “unusual” elements and polyatomic ions first

3. Balance Oxygen and Hydrogen atoms last

4. Keep track of your balancing acts!