Balancing Equations

Just repeat: “I know I can, I know I can!”

Balancing equations Conservation of Matter: During a chemical

reaction, atoms cannot be created or destroyed!

Due to the conservation of matter, equations MUST be balanced!

Thus, the total number of atoms in the products must equal the total number of atoms in the reactants

REMEMBER: The atoms are only being rearranged during the reaction!

Coefficients vs. Subscripts

Subscripts tell us how many atoms there are in the molecule.

H2O This tells us that there are 2 Hydrogen atoms bonded to one Oxygen atom

Coefficients tell us how many molecules there are.

2 H2O This tells us that there are 2 molecules of H2O

Coefficient

2H2OSubscript

Use of coefficients in balancing

When balancing a chemical equation, we can ONLY add coefficients! Coefficients do not change the molecules

in the reaction, they merely tell us how many molecules were needed for the reaction to occur.

We cannot add/change subscripts when balancing the equation. Any guesses why???

Don’t use subscripts!!!!

Because….. It changes the actual molecule!!! Which

would change either the reactant or the product! Example: H2O is water, but H2O2 is hydrogen

peroxide. That is a huge difference!

Ok, let’s try balancing some equations together!

How to balance an equation

FIRST STEP: Write out the equation with the reactants and products in the formula:

MgO + HBr ---> MgBr2 + H2O

(Magnesium oxide and Hydrogen Bromide becomes Magnesium Bromide and Water.)

How to balance an equation

SECOND STEP: Count the Atoms of each element on both sides of the equation.

MgO + HBr ---> MgBr2 + H2O

1 Mg 1 Mg1 O 1 O1 H 2 H1 Br 2 Br

How to balance an equation

THIRD STEP: Use coefficients to balance the equation

MgO + HBr ---> MgBr2 + H2O

We need a total of two hydrogen and bromine on the reactants side in order to balance this equation.

How to balance an equation

And we’re done! Our balanced equation:

MgO + 2HBr ---> MgBr2 + H2O

Double check your work, by counting again:1 Mg 1 Mg1 O 1 O2 H 2 H2 Br 2 Br

Try one on your own!

H + O H2O

H- 1 H- 2O- 1 O- 1

2H + O H2O

Let’s do another, for fun!!

Fe + HCl ---> FeCl2 +H2

1 Fe 1 Fe1 H 2 H1 Cl 2 Cl

Fe + 2HCl ---> FeCl2 +H2

Let’s try a couple more…N2 + O2 ---> N2O5

2 N 2 N2 O 5 O

We need to balance out the Oxygen first, then the Nitrogen. This gives us…

2N2 + 5O2 ---> 2N2O5

4 N 4 N10 O 10 O

One More…

C2H4 + O2 ---> CO2 + H2O

2 C 1 C4 H 2 H

2 O 3 O

C2H4 + 3O2 ---> 2CO2 + 2H2O