Chemical Formulas

The chemical formula for Aspirin = C9H8O4

Formulas show two things:

1. The elements in a compound and

2. The ratio of the different atoms that make up that substance.

Chemical Formulas Are Convenient

The chemical formula for a molecule of Aspirin is C9H8O4

• It would take a lot of writing to express this in words. Nine carbon atoms combined with eight hydrogen atoms combined with four oxygen atoms.

• C9H8O4 is a much more convenient and short way to write the aspirin molecule.

Chemical Equations

• Scientists use a shortcut for showing chemical reactions. It is called a Chemical Equation

Chemical Equations• This is a chemical equation.

• 2H2 + O2 2H2O

Hydrogen Oxygen Yields Water

CoefficientSubscript

Reactants Products

• In the molecular compound H2O, the number two is called a ________________.subscript

• How many atoms does the molecule H2O have? 3

• What are the names for the substances before a chemical reaction? _________________reactants

• What are the names for the substances after a chemical reaction? The products

• During a chemical reaction matter is not created nor destroyed. This principal is called Conservation of Mass.

• This means there will be the same number of atoms at the end of a reaction as there were at the beginning of the reaction.

Conservation of Mass

Conservation of Mass Example

• Read about conservation of mass on pages 154 and 155.

• Go to the “Out” section of your notes to answer the questions below.

1. What example was used to explain conservation of mass?

2. How does this example demonstrate conservation of Mass?

• During a chemical reaction matter is not created nor destroyed. This principal is called _________________________.Conservation of mass

The number placed at the front of an element or compound as seen in red below is called a ___________________?

2 SO2

coefficient

Is This a Balanced Equation?

• H2 + O2 H2O

•No! There are 4 atoms on the reactant (left) side of the equation and 3 atoms on the product (right) side?

• Can you balance this equation by adding a subscript? Why or why not?

H2 + O2 H2O

No! Subscripts cannot be added to balance an equation. You can only add coefficients.

H2 + O2 H2O2 2

• The number of reactants and products can ______________.

• What is it called when the same number of atoms exist on both sides of a chemical equation? The equation is said to be ______________________.

1. Synthesis (When two or more reactants combine.)

Example:

Three Types of Reactions

2SO2 + O2 + 2H2O 2H2SO4

2. Decomposition (When reactants break down into simpler products)

Example: 2H2O2 2H2O + O2

3. Replacement (When one element replaces another in a compound, or when two elements in different compounds trade places.

Example: 2CuO + C 2Cu + CO2

• What type of reaction would this be?

2 SO2 + O2 + 2H20 2H2SO4

This is a Synthesis Reaction

• What type of reaction would this be?

2NH4NO3 2N2 + O2 +4H2O

This is a Decomposition Reaction

• What type of reaction would this be?

P4O10 + 6H2O 4H3PO4

This is a Replacement Reaction

• What type of reaction occurs when an airbag inflates?

A Decomposition reaction in which a lot of nitrogen gas is created to quickly fill the airbag.