I II III IV V

A Balancing Act

Chemical Reactions

Chemical Reactions Take Place…

Every minute of every day both in and around you

Examples: Digestion Photosynthesis Car batteries-to start your car Rust

Reactions:

One or more substances, the ___________ change into one or more new substances, the __________. It is written as:

-Reactants → Products The arrow means

- “yields” or “reacts to produce”

reactants

products

Explanation:

An explanation was proposed by _____________ who stated in his atomic theory that in a chemical reaction, the way in which atoms are joined together are changed.

As reactants are converted to new products, __________that hold atoms together are __________ and new ones are formed.

Dalton

bonds

broken

Explanation:

Daltons atomic theory explains the ____________________________. Which States:

- In any physical or chemical change mass is neither created nor destroyed.

-The atoms in the products are the same atoms that were in the reactants, they are just arranged differently.

Law of Conservation of Mass

Explanation/Practice: In a word equation, reactants are written

on the ___________ and products are written on the ________.

Write the equation for… Copper can be produced by heating

copper (II) sulfide with oxygen. Sulfur dioxide is also produced.

Water is formed by the explosive reaction between hydrogen and oxygen

leftright

Answers

Copper(II)sulfide + Oxygen → Copper + Sulfer dioxide

Hydrogen + Oxygen → Water (Dihydrogen monoxide)

Meaning of Chemical Formula

Chemical Symbol Meaning Composition

H2O One molecule of water:

Two H atoms and one O atom

2 H2O Two molecules of water:

Four H atoms and two O atoms

H2O2 One moleculeof hydrogenperoxide:

Two H atoms and two O atoms

Meaning of Chemical Formula When a __________ is written after

the chemical symbol for an element it indicates the___________________.

When a coefficient is written in front of an atom or molecule it indicates the ____________ of that atom or molecule that is present.

If there are subscripts in that atom/molecule they need to be ____________ by the coefficient.

subscript

number

multiplied

# of that element

Reactants Products

UnbalancedTimberlake, Chemistry 7th Edition, page 164

Unbalanced and Balanced Equations

Cl

ClClCl

ClCl

ClH

H

H

HHH

H

H2 + Cl2 HCl (unbalanced) H2 + Cl2 2 HCl (balanced)

2 12 1 2 2

reactants products reactants products

2 2H

Cl

H

Cl

Timberlake, Chemistry 7th Edition, page 167

How do we go from Unbalanced to Balanced Equations? You ____________ change the

formula of your atom/ion/molecule! This means you may not change the

___________ ! Instead, you may put a coefficient

__________ of your atom/ion/molecule to balance the number of atoms after you have ___________ it by the subscript

MAY NOT

subscript

in front

multiplied

CH4 + 2 O2 CO2 + 2 H2O

Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

Timberlake, Chemistry 7th Edition, page 167

Balanced!

Balancing Steps

1. Write the unbalanced equation.

2. Count atoms on each side.

3. Add coefficients as needed to make #s equal on both sides of the

equation.

Coefficient subscript = # of atoms

4. Reduce coefficients to lowest possible ratio, if necessary.

5. Double check atom balance!!!

Helpful Tips

Balance one element at a time. Update ALL atom counts after adding

a coefficient. If an element appears more than

once per side, balance it last. Balance polyatomic ions as single

units. “1 SO4” instead of “1 S” and “4 O”

Al + CuCl2 Cu + AlCl3

Al

Cu

Cl

1 1

1 1

2 3

2

3

6

3

33 2

Balancing Example

Aluminum and copper(II) chloride react to form copper and aluminum chloride.

2

2

6

More Examples…

P + O2 → P4O10

H2 + O2 → H2O

BaCl2 + H2SO4→ BaSO4 + HCl

Cu + AgNO3 → Cu(NO3)2 + Ag

CaCO3 + HCl → CaCl2 + H2CO3

4 5

2 2 2

2

2 2

2