Week 27/28 Balanced Equations/Stoichiometry Lesson

Balancing Chemical Equations

As you fill in your notes sheet, look for the BOLD RED text.

2H₂ + O₂ ---> 2H₂O

This equation is BALANCED on both sides.

Notice that there are 4 Hydrogens and 2 Oxygens on each side.

The full-size numbers to the LEFT of the elements/compounds are called COEFFICIENTS and are the ONLY VALUES YOU CAN CHANGE.

The small numbers to the right of the elements are called SUBSCRIPTS and MUST STAY THE SAME in the equation.

In this example, we want the number of Mg (Magnesium) on the LEFT of the arrow to be the same on the RIGHT of the arrow.

We also want the number of O (Oxygen) to be the same number on both the LEFT and RIGHT of the arrow.

Once we count up the Mg and O on both sides, we can see what needs to change.

We CANNOT TAKE ANYTHING AWAY.

We can ONLY ADD using coefficients.

You'll see this done in the next slide...

REMEMBER

# of each element in reactants

MUST EQUAL

# of each element in products

2Al₂(CO₃)₃

• Al: 4 because 2 x 2 = 4

• C: 6 because 2 x 3 = 6

• O: 18 because 3 x 3 x 2 = 18

A few hints:

• Water can often be split into H + OH, but not always

• Save O for last in a reaction that produces CO2 + H₂O

• Polyatomics can be left as one thing if it appears on both sides of the yield

• Balance everything other than O and H first

• Try to get rid of odd numbers first

Balancing Chemical Equations

What is a molecule?

LET'S TAKE IT STEP BY STEP AND PRACTICE

Multiple Choice

LOOKING AT JUST THE SUBSCRIPTS, TELL ME HOW MANY CARBON ATOMS ARE LSITED

C12H22O11

• 11

• 22

• 12

• 1

Multiple Choice

LOOKING AT THE COEFFICIENT , TELL ME HOW MANY BROMINE ATOMS ARE LISTED: 12NaBr

• 1

• 0

• 12

• 24

Multiple Choice

LOOKING AT THE COEFFICIENTS AND THE SUBSCRIPTS, TELL ME HOW MANY OXYGEN ATOMS ARE LISTED:

3CO2

• 3

• 2

• 6

• 1

Multiple Choice

What coefficient should be used to make the following equation balanced?
N₂+O₂--> _NO 

• 1
• 2
• 3
• 4

Multiple Choice

How many HCl molecules do you need to balance this equation? 
Mg +  __HCl --->  MgCl₂ + H₂

• 1
• 2
• 3
• 4

Multiple Choice

Is the following equation balanced?
4Fe + 3O₂ --> 2Fe₂O₃

• yes
• no

Multiple Choice

Is this balanced?
Al + O₂ → 2Al₂O₃

• Yes
• No

Balancing Chemical Equations

​

What is a molecule?

LET'S TAKE IT STEP BY STEP AND PRACTICE

Multiple Choice

LOOKING AT JUST THE SUBSCRIPTS, TELL ME HOW MANY CARBON ATOMS ARE LSITED

C12H22O11

• 11

• 22

• 12

• 1

Multiple Choice

LOOKING AT THE COEFFICIENT , TELL ME HOW MANY BROMINE ATOMS ARE LISTED: 12NaBr

• 1

• 0

• 12

• 24

Multiple Choice

LOOKING AT THE COEFFICIENTS AND THE SUBSCRIPTS, TELL ME HOW MANY OXYGEN ATOMS ARE LISTED:

3CO2

• 3

• 2

• 6

• 1

Multiple Choice

What coefficient should be used to make the following equation balanced?
N₂+O₂--> _NO 

• 1

• 2

• 3

• 4

Multiple Choice

How many HCl molecules do you need to balance this equation? 
Mg +  __HCl --->  MgCl₂ + H₂

• 1

• 2

• 3

• 4

Multiple Choice

Is the following equation balanced?
4Fe + 3O₂ --> 2Fe₂O₃

• yes

• no

Multiple Choice

Is this balanced?
Al + O₂ → 2Al₂O₃

• Yes
• No

Open Ended

What does a chemical reaction tell you?

Multiple Choice

Can we use mole ratios to calculate how much product is produced from a known amount of reactant?

• Yes

• No