Balancing Equations and mols

Some Rules...

Remember...when elements are in a chemical reaction, they form a new substance

Example: Sodium and Chlorine react to form Salt (Sodium Chloride)

RULE ONE: In a compound name, The cation (positive charge) is written before the anion (negative charge)

Example: NaCl because Na+ and Cl-

You Try

rule one

atoms vs molecules

RULE TWO:

when we have the smallest amount of an element that can still maintain all of the element’s properties we call that an ________________?

When we have the smallest amount of a compound that can still maintain all of the compound’s properties we call that a _____________?

You try

rule two

How many Atoms?

When we write atoms and molecules out there are often numbers that come before and after in the formulas.

Rule 3: If the number comes after (is to the right) of an element name and is subscript, it is the number of atoms of that element (if no number there is one atom):

Ex: H2 has two atoms of H or H-H

Ex: H has one atom of H

Ex: H2O has two atoms of H and one atom of O

Number of molecules

If a compound is bracketed, the number that follows refers to the number of molecules of that compound.

Ex: (SO4)6 has 6 molecules of SO4

This means there are 6 atoms of S and 6 x 4 atoms of O (24 atoms of O).

Ex: H2(CO2)2 has 2 atoms of H and 2 molecules of CO2

2 molecules of CO2 have 2 atoms of C and 2 x 2 atoms of O (4 atoms of O).

You Try

Rule Three

The numbers in FrontRule 4: The numbers that come before the names of elements and compounds in chemical equations refer to the number of atoms or molecules that are written after the number

These are the ONLY numbers that can be changed to balance equations!!!!!

Ex: 4H2O means 4 molecules of H2O (8 H and 4 O total)

Ex: 2H2SO4 + 4CO2 means 2 molecules of H2SO4 and 4 molecules of CO2

How many total H, S, O in 2H2SO4?

You try

Rule 4...

Balancing Equations

We write out chemical reactions in equations with the reactants(what you start with) on the left side and products(what you end up with) on the right side

Ex: Sodium and Chlorine react to form Sodium Chloride

Na + Cl2 NaCl

PROBLEM: we started with two atoms of Cl but ended with only one!

Balancing Equations

We must fix our problem by changing the numbers of reactants and/or products to balance

WE CANNOT END UP WITH MORE OR LESS ATOMS THEN WE STARTED WITH!

For Na + Cl2 NaCl we must add a 2 to the front of Na and a 2 to the front of NaCl

2 Na + Cl 2 NaCl Now it is balanced

Try with this way

H2 + O2 H2O H

HH HH OO OO

OO

HH HHç√ç√

OOOO

HHHH

HHHH HH

OO

HHHH

OO

HHç√ç√

2 H2 + O2 = 2H2O

You Practice

Balancing Equations