PART 1:

Introduction to Chemical Reactions9a

In a chemical reaction…

atoms are____________

(fill in the blank)

What are some common reactions in your everyday life?

How can you tell when a chemical reaction has

taken place?

Formation of a ___________________

also known as a ___________________

HOW DO CHEMISTS REPRESENT CHEMICAL

REACTIONS?

Chemists use ______________ to represent chemical reactions. The starting substances are

__________________What you

end up with are _____________When do you use chemical equations in your own life?

REAL LIFE EXAMPLE: You are going to bake cookies. You know that:

____flour + ____sugar + ____baking powder + ___butter + ___chocolate chips makes ___cookies

This is a _______________EQUATION. What are the product(s)? What are the reactant(s)?

What else do you need to know….

if you already know that you need to bake them at 350 for ½ hour??

You need to know the _________________

______________________ of the ingredients with respect to each other.

In other words, you need a

___________________ ________________ (Remember – cooking is chemistry!!)

HOW MIGHT A CHEMIST USE A

CHEMICAL EQUATION?

You are an EVIRONMENTAL CHEMIST concerned about

GLOBAL WARMING

You are asked to determine how much carbon dioxide will be produced from the amount of methane burned by a factory. The first thing you need is a WORD EQUATION

methane + oxygen yields

carbon dioxide + water

Word equations are clunky and they don’t tell you very much… You can make your equation less clunky if you use

_________________________instead of words.

__ CH4 + __O2

__CO2 + __ H2O

This type of equation is a

____________

equation.

In addition, to give more information in an equation, symbols are used to

represent the _____________________ of the substances, including:

Solids = _______ Aqueous = ______Gases = _______ Liquids = ______

(Aqueous means __________________

_________________________________

__ CH4(g) + __ O2(g)

__ CO2 (g) +__ H2O(l)

This equation still doesn’t have enough information…What else do you need?

What law allows us to balance equations? State this law.

CH4

O2

CO2

H2O

A very important rule in balancing equations: never change the

________________________

For example: ______ cannot be changed to _______

PART 2

BALANCING EQUATIONS

The Skill

The Law of Conservation of Mass says…

You must have the same number of atoms of a particular element on

both sides of a chemical equation…

i.e., the equation must be BALANCED!

There are 2 different types of numbers in chemical equations.

COEFFICIENTS

__ CH4 + 2 O2 __CO2 + 2 H2O

SUBSCRIPTS

Subscripts cannot be changed while balancing an equation…remember CO vs CO2?

However, COEFFICIENTS can be changed in order to balance an equation.

Begin by counting the number of atoms of each element…

___ Na(s) + ___ Cl2 (g) ___ NaCl (s)

___H2 (g) +___ N2 (g) ___ NH3 (g)

__ Al2O3(s) ___ Al(s)+ ___O2(g)

___ Fe(BrO3)3 → ___ FeBr3 + ___ O2

ANOTHER RULE: If you balance an equation, and

then find that all of the coefficients are divisible by a common number,

you must divide them by that number…

2CH4 + 4O2 2CO2+4H2O

WRONG!

CH4 + 2O2 CO2+2H2O

RIGHT!!

Hint #1If a polyatomic ion appears

unchanged on both sides of the equation, balance it as a UNIT

– not as individual atoms

__Al(NO3)3 + __LiOH

__LiNO3 + __ Al(OH)3

[ ]

[ ][ ]

[ ]

Al(NO3)3

[ ]

[ ]

[ ]Al(OH)3

][LiOH LiNO3

__(NH4)3PO4 +__ BaSO4

__(NH4)2SO4 +__Ba3(PO4)2

Example of an acid-base reaction.

__ H2SO4 + __KOH ___K2SO4 + __ H2O

Hint #2 First, balance an element that only appears in one reactant

and one product (leaving oxygen to last and hydrogen to

second last.)

__C3H8 +__O2 __CO2 + __H2O

__C5H12 (g)+__O2(g)

__CO2(g) + __H2O(l)

HINT #3If you balance all of the elements and the polyatomic ions, except for one element, and there’s an odd # of that last element on one side, and an even number on the other side – balance that element with a fractional number (containing ½) and

then double all of the coefficients

__C5H10 + __O2 __CO2 + __H2O

__C6H14 + __O2 __CO2 + __H2O