5.4 To represent chemical change in the form of balanced equations

Balancing Equations

All matter is made up of atoms

Atoms combine in chemical reactions to form compound

Each element has the same type of atoms

NaOHNa – 1 atomO - 1 atomH - 1 atom

NH4NO3

N - 2 atomsH - 4 atomsO - 3 atoms

C3H5(NO3)2 C - 3 atomsH - 5 atomsN - 2 atomsO - 6 atoms

TRICKY

4 C2H4 C - 8 atomsH - 16 atoms

Watch outfor the # in front!

The number in front of the entire molecule tells how many molecules there is. In this

example there are 4 molecules!

C has 2 atoms but there are 4 molecules so

that means there is 8 atoms all together

How many atoms are in each element for these compounds?

H – 1 atomN – 1 atomO – 3 atoms

H – 4 atom

N – 4 atomO – 12 atoms

Cu – 4 atom S – 2 atom

1. HNO3 2. 4HNO3 3. 2Cu2S

4. NH4NO3 5. 2Fe2SO4

N– 2 atomH – 4 atomO – 3 atoms

Fe– 4 atomS – 2 atomO – 8 atoms

H – 2 atomN – 2 atomO – 6 atoms

Cu – 1 atom

O – 4 atomS – 1 atoms

Ca – 2 atom O – 4 atom H – 4 atoms

9. 4C3H5(NO3)2 10. 4Fe2SO4C– 12 atomN – 8 atomH – 20 atomsO – 24 atoms

Fe– 8 atom

S – 4 atomO – 16 atoms

6. 2HNO3 7. CuSO4 8. 2Ca(OH)2

In all chemical reactions, the number of atoms of each element in the reactants will be equal to the number of atoms of each element in the products.

2H2 + O2 2H2O (balanced equation)

Reactants = Products

Hydrogen (H) = 4 atoms Oxygen (O) = 2 atoms

Hydrogen (H) = 4 atomsOxygen (O) = 2 atoms

0.5 L

NaOH + HCl NaCl + H2O

First list all the elements separately on each side

Na = Na =O = O =H = H =Cl = Cl =

Reactants = Products

Count all your atoms for each element

1 atom 1 atom1 atom 1 atom2 atoms 2 atoms1 atom 1 atom

YES…it is a

balanced equation

0.5 L

H = H = O = O =

2 2 2H O H O Reactants = Products

First list all the elements separately on each side

0.5 L

H = 2 atoms H = 2 atomsO = 2 atoms O = 1 atom

2 2 2H O H O Second, count the number of atoms for the reactants and # of atoms for the products for each element

Reactants = Products

These are not the

same…..so this equation is

NOT balanced!

0.5 L

H = 2 atoms H = 2 atomsO = 2 atoms O = 1 atom

2 2 2__ __ ___H O H O

NEVER EVER add a number directly into compound!!! (only in front!)

2

2

44

2

2 2 22 2H O H O The final balanced equation is

Never Here!

Add a number (co-efficient) in front of one or more of the molecules to make the equation balanced.

Fe2O3 + C CO2 + Fe Reactants = Products

Fe = Fe =O = O =C = C =

2 atoms 1 atom3 atoms 2 atoms1 atom 1 atom

6 64

33

4

The final balanced equation is:

2 3 22 3 3 4Fe O C CO Fe

Al + CuCl2 AlCl3 + Cu Reactants = Products

Al = Al =Cu = Cu =Cl = Cl =

1 atom 1 atom1 atom 1 atom2 atoms 3 atoms6 63

223

The final balanced equation is:

2 32 3 2 3Al CuCl AlCl Cu

Na2CO3 + Ca(OH)2 CaCO3 + NaOH Reactants = Products

Na = Na =C = C =O = O =H = H =Ca = Ca =

2 atoms 1 atom1 atom 1 atom5 atoms 4 atoms2 atoms 1 atom1 atom 1 atom

52

2

2 3 2 3 Na CO + Ca(OH) CaCO + 2 NaOH

A solution of sodium carbonate (Na2CO3) reacts with a solution of calcium hydroxide (Ca(OH)2) to give precipitate of calcium carbonate (CaCO3) and a solution of sodium hydroxide (NaOH). Write a balanced equation for this reaction

o When balancing equationso First list elements on each sideo Second count atoms for each

elemento Add a number in front of molecule

to balance the atoms

o NEVER EVER add a number in between a molecule!!! (always put it in front)

WORKSHEET # 11 Study guide, Module 3, page 38