Balancing Chemical Equations

​Remember that sometimes a Catalyst can be used to cause a reaction but it does not enter into the reaction.

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 coefficients, which we will then multiply the quantity following.

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

Counting the TOTAL number of atoms in a molecule

Counting the TOTAL number of atoms in a molecule

Multiple Choice

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

• 1
• 2
• 3
• 4

Multiple Choice

What is the total number of atoms present in 5Na₃PO₄?

• 5

• 55

• 40

• 8

Multiple Choice

Is the following equation balanced?

Al + O₂ ---> 2Al₂O₃

• YES

• NO

Multiple Choice

What is the right part of a chemical equation called?

2H₂ + O₂ ---> 2H₂O

• Reactants

• Yields

• Products

• Chemical Equation

Multiple Choice

How many Oxygens are in this molecule? 
(OH)₂

• 4
• 1
• 2
• 3

Multiple Choice

What is the left part of a chemical equation called?

2H₂ + O₂ ---> 2H₂O

• Reactants

• Yields

• Products

• Chemical equation

Multiple Choice

What is the little number after an element in a chemical equation called?

Example: H₂

• Coefficient

• Atom

• Subscript

• Equation

Multiple Choice

What is the number before a chemical formula called?

Example: 2H₂ + O₂ ---> 2H₂O

• Coefficient

• Atom

• Subscript

• Equation