Balancing Chemical Equations

Balancing Chemical Equations

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

Multiple Choice

What does the Law of Conservation of Mass say? It says,

"During a chemical reaction, mass is neither _______ or destroyed."

• burned

• created

• melted

Multiple Choice

The substances that go into a reaction are called the _______.

• products

• reactants

Multiple Choice

So, the Law of Conservation of Mass would tell us that the mass of all the REACTANTS must __________ the mass of all PRODUCTS in a chemical reaction.

• equal

• be greater than

• be less than

Multiple Choice

An ENDOTHERMIC reaction would feel ______ to the touch, while an EXOTHERMIC reaction would feel ______ to the touch.

• hot ; cold

• cold ; hot

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...