# How to balance - PowerPoint PPT Presentation

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How to balance. IPC unit 4 (Make sure to click “view show” to follow the correct process). Why we balance. Everything that goes into a chemical equation must be accounted for (This is the law of conservation of mass: Matter cannot be created or destroyed )

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How to balance

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## How to balance

IPC unit 4

(Make sure to click “view show” to follow the correct process)

### Why we balance

• Everything that goes into a chemical equation must be accounted for (This is the law of conservation of mass: Matter cannot be created or destroyed)

• This is also helpful because we can see how much product (right side of the equation) that we will get depending on the amount of reactant (left side) that we put in.

### Example:

• Hydrogen peroxide decomposes into water and oxygen.

• Balance the equation: H2O2 H2O + O2

### Cont.

• We cannot change the subscript (the little numbers) because that would change the chemical formula and then it would be a completely different chemical. What we can do is put a big number in the front of each compound. The number we put in the front is called the coefficient. We use coefficients to balance chemical equations.

### There are two ways to do this.

• Think of the arrow as an equal sign. You can go back and forth and make sure you have the same number of each element on both sides, or you can use the chart method to get you started.

### Chart method

H2O2 H2O + O2

ReactantProduct

2 H 2

2 O 3

I have 3 Oxygens (O) on the right because the first one adds to the second two. Use the plus sign to help you remember to add. My Hydrogens (H) match, but my Oxygens (O) don’t so I need to fix them. When I put a coefficient in front it will multiply everything in the formula.

H2O22H2O + O2

I now have:

ReactantProduct

2 H 2 4

2 O 3 4

### I need to go back and match my left side. I’ll put a 2 in front of Hydrogen Peroxide (H2O2).

2H2O22H2O + O2

Now I have:

ReactantProduct

4 2 H 2 4

4 2 O 3 4

Both sides match so I am done. If you ever get stuck, just try different numbers to see what will happen. It’s smart to use a pencil on these.

• Make sure that you can’t reduce your coefficients any more than they already are. For example: 2Cu +4AgNO34Ag +2Cu(NO3)2

• I can divide all of the coefficients by 2, so I should have: Cu +2AgNO32Ag +Cu(NO3)2

### Get out your “balancing chemical equations” paper

• H2 + N2 NH3

Reactants Products

2 H 3

2 N 1

3

2

6

6

2

• C + H2O  CO + H2

Reactants Products

1 C 1

2 H 2

1 O 1

The equation is already balanced so

you just need to write “balanced”underneath the equation

• AgNO3 + FeCl3 AgCl + Fe(NO3)3

Reactants Products

1 Ag 1

1 N 3

3 O 9

1 Fe 1

3 Cl 1

The number outside the parentheses multiplies what is inside

3

3

• AgNO3 + FeCl3 AgCl + Fe(NO3)3

Reactants Products

1 Ag 1

1 N 3

3 O 9

1 Fe 1

3 Cl 1

3

3

3

9

3