Balancing Equations

Chapter 13.2

Standards:

• GLE 0807.9.4– Distinguish among elements, compounds, and

mixtures.• GLE 0807.9.9– Explain the law of conservation of mass

• GLE 0807.9.8– Interpret the events represented by a chemical

equation

Key concepts:

• Interpret and write simple chemical formulas• Identify the reactants and products of a

chemical reaction.

Key Vocabulary:

• Reactant• Product• Law of conservation

of mass

What do you already know?

• Where do you find reactants? • Where do you find products?• Why do we use symbols instead of

writing out everything?• What does conservation mean?

Now imagine having to write out names!

Let’s talk compound vs. element:

• Is it a compound or element?

He

Let’s talk compound vs. element:

• Is it a compound or element?• How many atoms?

CO2

Let’s talk compound vs. element:

• Is it a compound or element?• How many atoms?

NaClO

Chemical Reaction:

• Chemical equation uses symbols and formulas to describe a chemical reaction.

• Parts:– Reactants—starting materials– Products—what you make– Yield—this is the arrow sign• This usually means that energy is going

in or out

Think of this a piece of sheet music...

Cheat sheet time!

Reactants point to products

R P

Balancing Equations:

• Conservation means the before is equal to the after…meaning whatever we do to the reactants, we must do to the products.

• All atoms must be equal• Law of conservation of mass states

that the mass is neither created nor destroyed in a chemical change. – Reactants = Products

How many atoms?-H20-C6H1206

-CH4

R P

Balancing the Parts:

• Important parts:– Coefficient: the number that is place

in the front of a symbol• This is what WE will use to balance the

equation

– Subscripts• Number written below and to the right

of the symbol

How many atoms?-H20-C6H1206

-CH4

Balancing the Parts:• How to balance:

1. Determine the number of atoms for each element

2. Pick an element that is not equal on both sides (start with metals)

3. Add a coefficient in front the formula with that element and adjust your counts

4. Continue to add coefficients to get the same number of atoms of each side

Remember to keep track of the atoms!

Practice times

Balancing Equations

• Hydrogen and oxygen are diatomic elements.

• Their subscripts cannot be changed.• The subscripts on water cannot be

changed.

Hydrogen + oxygen water

H2 + O2 H2O

Balancing Equation

• Count the atoms on each side.–Reactant side: 2 atoms H and 2

atoms O–Product side: 2 atoms H and 1

atom O

H2 + O2 H2O

Balancing Equations

•H2 + O2 H2O

• If the subscripts cannot be altered, how can the atoms be made equal?

• Adjust the number of molecules by changing the coefficients.

Balancing Equations

• Reactants: 2 atoms of H and 2 atoms of O

• Products: 4 atoms of H and 2 atoms of O

• H is no longer balanced!

H2 + O2 2H2O

Balancing Equations

• Reactant side: 4 atoms of H and 2 atoms of O

• Product side: 4 atoms of H and 2 atoms of O

• It’s Balanced!

2H2 + O2 2H2O

Balancing Equations

• Count atoms.–Reactants: 2 atoms N and 2 atoms

H–Products: 1 atom N and 3 atoms of

NH3

N2 + H2 NH3

Nitrogen + hydrogen ammonia

Balancing Equations• Nothing is balanced.• Balance the nitrogen first by

placing a coefficient of 2 in front of the NH3.

N2 + H2 2NH3

Balancing Equations• Hydrogen is not balanced.• Place a 3 in front of H2.

• Reactant side: 2 atoms N, 6 atoms H

• Product side: 2 atoms N, 6 atoms HN2 + 3H2 2NH3

We need practice!

• On the back of your notes, let’s practice.• Do not write on the hand-outs. I will take

these up when you leave.– Balancing Act

Pearls of Wisdom:

• How do you balance equations?• What are some important steps?

Homework:

• Finish your worksheet.