CHEMICAL REACTIONS AND EQUATIONS

1. IN A CHEMICAL REACTION, SUBSTANCES CALLED THE REACTIONS ARE CONVERTED INTO SUBSTANCES CALLED PRODUCTS.

2. CHEMICALS REACT TO BECOME MORE STABLE.

3. CHEMICAL REACTIONS ARE REPRESENTED BY CHEMICAL EQUATIONS THAT ARE SHORTHAND SENTENCES. THEY ARE MADE UP OF THE FOLLOWING:

A. SYMBOLS = ELEMENTS EX. CO COBALT

SYMBOLS REPRESENT ATOMS

B. FORMULAS = 2 OR MORE ATOMS COMBINED EX. O2

THIS IS NO LONGER AND ATOM IT IS 2 ATOMS

COMBINED FORMING A MOLECULE

ANOTHER EX. CO THIS IS A MOLECULE OF CARBON MONOXIDE.

TWO ATOMS COMBINED MAKES A MOLECULE

C. 2 Co = 2 ATOMS OF COBALT. THE 2 IS THE COEFFICIENT

AND TELLS HOW MANY ATOMS OR MOLECULES ARE THERE.

D. 02 = 1 MOLECULE OF OXYGEN. THE 2 IS A SUBSCRIPT AND

TELLS HOW MANY ATOMS OR MOLECULES ARE THERE.

E. + = REACTS WITH ON REACTANTS SIDE OR AND ON PRODUCTS

SIDE

F. → OR = MEANS TO FORM

REACTANTS PRODUCTS

EX. 2 Ca + 02 → 2Ca0

COEFFICIENT SUBSCRIPT

2 ATOMS OF CALCIUM REACTS WITH 1 MOLECULE OF OXYGEN

TO FORM 2 MOLECULES OF CALCIUM OXIDE

TYPES OF CHEMICAL REACTIONS

1. THERE ARE MANY TYPES OF CHEMICAL REACTIONS.

HOWEVER MOST REACTIONS FALL INTO 4 BASIC TYPES.

A. DIRECT COMBINATION A + B → AB

2 Na + C12 → 2 NaCl

B. DECOMPOSITION AB A + B

2 H2O → 2 H + O

C. SINGLE REPLACEMENT A + BX → AX + B

Zn + 2HCl → ZnCl2 + H2

D. DOUBLE REPLACEMENT AX + BY → BX + AY

CaCO3 + 2 HCL H2CO3 + CACl2

BALANCING EQUATIONS

1. WHEN CHEMICALS REACT THERE HAS TO BE AS MANY

ATOMS OF AN ELEMENT ON THE REACTANT AND PRODUCT

SIDE OF AN EQUATION. (CONSERVATION OF MATTER)

2. TO BALANCE AN EQUATION YOU CAN’T CHANGE THE

NUMBERS WITHIN A MOLECULE. (H2O). THE 2 CAN’T

CHANGE. ELECTRONS HAVE REACHED THE OCTET RULE.

THIS IS STABLE AND WON’T CHANGE. YOU CHANGE THE

NUMBERS IN FRONT OF THE MOLECULE CALLED THE

COEFFICIENT. THIS CHANGES THE NUMBER OF

MOLECULES BUT NOT THE STABLE MOLECULE ITSELF.

3. THE PROBLEM MOST STUDENTS HAVE IS

UNDERSTANDING WHAT THE SYMBOLS MEAN.

A. 2A12 (SO4) 3 MEANS THERE ARE 2

MOLECULES WITH 2 Al IN EACH MAKING A TOTAL OF 4

Al. IT MEANS THERE ARE 3 SO4 POLYATOMIC IONS.

THIS MAKES 6 S AND 24 O IN THE TWO MOLECULES.

4. WHEN BALANCING START WITH THE SIMPLEST

COMBINATION FIRST.

CH4 + O2 → CO2 + H2O

DON’T START WITH THE OXYGEN. IT HAS THREE

PLACES TO BALANCE AT ONCE.

5. WHEN THE NUMBERS GET COMPLEX, USE FRACTIONS

AND THE MULTIPLY BY A SMALL WHOLE NUMBER TO

ELIMINATE THE FRACTION.

Al + O2 → Al2O3

2 Al + 1 ½ O2 → Al203

MULTIPLY BY 2

4 Al + 3 O2 → 2Al203