Balancing Equations tutorial

• This tutorial will take you through steps necessary to balance chemical equations.

Law of the Conservation of Mass

• The law of conservation of mass states that the mass of the starting material equals the mass of all products at the end of the reaction.

• In chemical terms, mass is equivalent to the elements involved.

Consequences

• If the Law of conservation of mass was not correct:

• Imagine eating a sandwich---- a chemical reaction that occurs in your mouth----if the law of conservation of mass did not exist, your food could disappear (or increase in size) from time to time.

Steps to solve a balancing equations problem

• Organize your information

• Examine the formulae in the problem

• Check rows and columns to keep track of the problems.

Sample problem

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

Step 1: SetupThe double line is like an equal

sign. __ KCl + __ Fe2O3 => __ K2O + __ FeCl3

Step 2: Initial inventoryList elements (or ions).

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K

Cl

Fe

O

Step 3: Inventory formulas

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K __ x 1 __ x 2

Cl __ x 1 __ x 3

Fe __ x 2 __ x 1

O __ x 3 __ x 1

Step 4: Check set-up

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K __ x 1 __ x 2

Cl __ x 1 __ x 3

Fe __ x 2 __ x 1

O __ x 3 __ x 1

All numbers match the formulas.

Step 5: Filling in the table

• Here are the basic rules and hints:– For each row, the left side of the double line must equal

the right side of the double line.

– For each column, Each underlined number MUST be the same.

– Begin in a row where the numbers are not the same.

– When you fill in row, continue from the numbers that you filled in. DO NOT JUMP AROUND THE TABLE.

Start with row of ClLeast common multiple of 1 and 3 is 3.

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K __ x 1 __ x 2

Cl _3 x 1 1 x 3

Fe __ x 2 __ x 1

O __ x 3 __ x 1

Since we see a 3 underlined in the first column, we can enter a three in the row above

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _3 x 1 __ x 2

Cl _3 x 1 1 x 3

Fe __ x 2 __ x 1

O __ x 3 __ x 1

We have a problem here. The number that would fit in the Potassium row would be 1.5, but all numbers

must be whole numbers so multiple by 2.

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _3 x 1 __ x 2

Cl _3 x 1 1 x 3

Fe __ x 2 __ x 1

O __ x 3 __ x 1

We have a problem here. The number that would fit in the Potassium row would be 1.5, but all numbers

must be whole numbers so multiple by 2.

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _6 x 1 __ x 2

Cl _6 x 1 2 x 3

Fe __ x 2 __ x 1

O __ x 3 __ x 1

Continue on with the potassium row

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _6 x 1 _3 x 2

Cl _6 x 1 2 x 3

Fe __ x 2 __ x 1

O __ x 3 __ x 1

Now the Potassium oxide column

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _6 x 1 _3 x 2

Cl _6 x 1 2 x 3

Fe __ x 2 __ x 1

O __ x 3 _3 x 1

Now the oxygen row

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _6 x 1 _3 x 2

Cl _6 x 1 2 x 3

Fe __ x 2 __ x 1

O _1 x 3 _3 x 1

Now the Iron (III) oxide column

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _6 x 1 _3 x 2

Cl _6 x 1 2 x 3

Fe _1 x 2 __ x 1

O _1 x 3 _3 x 1

Now the Iron row.

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _6 x 1 _3 x 2

Cl _6 x 1 2 x 3

Fe _1 x 2 2 x 1

O _1 x 3 _3 x 1

The underlined numbers in the Iron (III) chloride column match. This is a good sign.

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _6 x 1 _3 x 2

Cl _6 x 1 2 x 3

Fe _1 x 2 2 x 1

O _1 x 3 _3 x 1

Check to see if each row equals out on the left and right sides of the double lines.

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _6 x 1 _3 x 2

Cl _6 x 1 2 x 3

Fe _1 x 2 2 x 1

O _1 x 3 _3 x 1

Check to see if each underlined number in each column is the same.

__ KCl + __ Fe2O3 => __ K2O + __ FeCl3

K _6 x 1 _3 x 2

Cl _6 x 1 2 x 3

Fe _1 x 2 2 x 1

O _1 x 3 _3 x 1

The numbers all check, so we can fill in the coefficients in the equation.

6 KCl + 1 Fe2O3 => 3 K2O + 2 FeCl3

K _6 x 1 _3 x 2

Cl _6 x 1 2 x 3

Fe _1 x 2 2 x 1

O _1 x 3 _3 x 1

You are done.

The answer is

6 KCl + 1 Fe2O3 => 3 K2O + 2 FeCl3