Do Now:

1. What is a chemical formula? Give an example.

2. What is a chemical equation?

3. What does the law of conservation of mass/matter say?

AGENDA Title: Balancing Equations Standard___1) Do Now2) Chemical Formula Practice Homework: Chemical

Formulas Practice 3) Intro to Balancing Equations

Chemical Formulas• We KNOW, a chemical formula is the combination of

elemental symbols that are in a substance, • … but what are those numbers?

Subscript• A subscript is the number written below and to the RIGHT of the chemical symbol.

• It means there are that many of those atoms.• If there is no subscript, that means only one atom of the element is there. Ex. NaCl

• “Sub” means “under”. The subscript is UNDER the chemical symbol!

CO2

H2OMgCl2

Subscript

Coefficient• A coefficient is the number placed in FRONT of a chemical symbol or formula.

• You MULTIPLY the number (subscript) of each element in the formula by this number.

2CO3H2O

Coefficient

Subscript

Label the subscript and coefficient:

1. C6H12O6

2. 2HCl

3. 3NaO2

4. NaHO5

5. CuS2

6. N2CO3

7. CaSO4

8. Fe2O3

9. 4NaOCl

10. Al2SO4

Chemical Formulas and Counting Atoms Practice!

• Work with your table partner to finish the worksheet front and back.

• This activity is…• 12 inch voices• Stay seated!

• Well go through the front side together…

Creating Chemical Formulas

Once we understand formulas…

•We can look at equations!

Review of Formulas•3HCl2

•CH(NaO3)2

•4NOH2O

•2Mg2(Cl2O)3

Steps:1.ID the elements2.Count up the

subscripts3.Get rid of the

parentheses4.Distribute the

coefficient

Chemical Equations• Chemical equations are used to describe reactions.

• A chemical equation uses chemical formulas and symbols as a short way to describe a chemical reaction. • Ex. C + O2 CO2

• H + O H2O

• Finish this chemical equation: Na + Cl ______

Balancing equations• The Law of Conservation of Matter (Mass tells us that

the mass of the reactants that we start with, HAS TO BE the same as the products that we end with.)

• When we write a CHEMICAL EQUATION, we want to make sure that it follows this law. We call it a “balanced equation”.

• This means that there is the same number of atoms of each element on EACH side of the equation (before and after)

The STEPS of Balancing Chemical

Equations

Conservation of Matter• Matter is NEVER created, nor destroyed

• Chemical Reaction

- elements and total # of atoms in the reactants must be the same for products

# of atoms before the reaction

= # of atoms after the reaction

reactant product

Knowing this, lets look back at that anticipation guide from last week…

H2 + O2 H2O

Reactant ProductBefore the reaction = after the reaction

What are the reactants?What are the products? What elements are present on both sides?Is the equation balanced (equal)? Why? How can the number of atoms on both sides of the equation be balanced?

1. Identify all the elements involved in the reaction:

H2 + O2 --> H2O

H

O

2. Count the number of atoms (use subscripts) of EACH element on BOTH sides:H2 + O2 --> H2O

- H -

- O -

2

2

2

1

reactants

product

3. Identify which side needs more atoms. Put COEFFICIENTS, MULTIPLY and RECOUNT the atoms. Do not change the formula.

H2 + O2 --> H2O2

- H -

- O -

2

2

2

1

4

2

BALANCED!!

H2 + O2 --> H2O

- H -

- O -

2

2

2

1

2

4

2

2

4

4. Do the same (C,M,R) on the other side until ALL the atoms on both sides are EQUAL.

EXERCISE: BALANCE THE EQUATION. FOLLOW THE STEPS.

H2 + Cl2 ---> HCl2

2. KClO3 --> KCl + O2

Practice together:

1. CaO Ca + O

2. N2 + H2 NH3

3. Fe + H2O Fe2O2 +

H2

3. Al2(SO4)3+ NaF→ Al F3 + Na2SO4

- Al -

- S -

- O -

- Na -

- F -

Now try it on your own!•This activity is:

• Independent•You are:

• In your seat•Working with your partner if you need help

•Using 12 inch voices

Homework

Finish the worksheet on balancing equations!