Transcript Gaussian Reflection

Balancing Equations
Section 7.3 in Textbook
Chemical Equations
The substances involved in a chemical
reaction before the change occurs are
called the reactants
The new substances formed after the
change are called the products
We say that reactants yield products
reactants products
yield
Using Equations to Represent Reactions
Reactants  Products
C(s) + O2(g)  CO2(g)
“1 carbon reacts with 1 oxygen molecule
yields 1 molecule of carbon dioxide”
The letters behind the chemical indicates
whether the substance is solid (s) or (cr),
liquid (l), aqueous solution (aq),
or gas (g).
Writing Chemical Equations
A chemical equation is a shorthand for the
expression of the reaction.
For example: Hydrogen gas reacts with
Oxygen gas to produce Dihydrogen
monoxide.
: can be written in shorthand as:
H2 + O2  H2O
Conservation Obeyed
In any chemical reaction, the conservation
of mass is observed
Principle of the conservation of mass
states: matter can not be created or
destroyed in a chemical reaction
Therefore, the mass of the reactants and
the mass products must be the same
Coefficients
A numbers in front of compounds or
elements in a chemical equation
represent the number of particles in
the reaction
The coefficients are used to balance
the equation to obey the law of
conservation of mass
2 H2 + O2 2 H2O
Balancing Equations
When balancing a chemical
reaction you may add
coefficients in front of the
compounds to balance the
reaction, but you may not change
the subscripts.
Changing the subscripts
changes the compound.
Steps to Balancing Equations
There are four basic steps to balancing
a chemical equation.
1.Write the correct formula
2.Find the number of atoms for each
element on each side.
3.Determine where to place
coefficients.
4.Check your answer to see if:
The numbers of atoms on both
sides of the equation are now
balanced.
The coefficients are in the lowest
possible whole number ratios.
(reduced)
Some Suggestions to Help You
-Take one element at a time, working
left to right except for H and O. Save
H for next to last, and O until last.
-IF everything balances except for O,
and there is no way to balance O with
a whole number, double all the
coefficients and try again. (Because O
is diatomic as an element)
-(Shortcut) Polyatomic ions that appear
on both sides of the equation should
be balanced as independent units
Balancing Equations
Keep track of the elements in a table,
adjusting the amount of atoms as you
put in coefficients
You must go back and forth putting in
coefficients until all of the atoms’
numbers are equal
Balancing Equations Practice
2.) Ca(NO3)2 + H2SO4  CaSO4 + HNO3
Balancing Equations Practice
3.) Fe + Cl2  FeCl3
Balancing Equations Practice
4.) Fe + O2 
Fe2O3
Balancing Equations Practice
5.) Zn + HCl  ZnCl2 + H2
Balancing Equations Practice
6.) Cu + AgC2H3O2  Cu(C2H3O2)2 + Ag
Balancing Equations Practice
*7.) H2O2 
H2O + O2
Balancing Equations Practice
*8.) Na + H2O 
NaOH + H2
Balancing Equations Practice
*9.) C2H6 +
O2  CO2 +
H2O
Balancing Equations Practice
10.) Fe + H2O 
Fe3O4 +
H2
Balancing Equations Practice
11.) Al2(SO4)3 + Ca(OH)2  Al(OH)3 + CaSO4