Transcript Balancing Equations

Balancing Equations
So far the equations tell us who is
reacting. Now we have to be able to
tell how much.
Learning Objectives
 Balance simple chemical equations.
 Determine reactant and product Moles in
a balanced chemical equation.
 Determine the mass of reactants and
products involved in a simple chemical
equation. *
Balancing Equations
 The Law of Conservation of Matter states that
matter is neither created nor destroyed in a
chemical reaction.
 Each element present in the reactants must still be there
as products.
 Ex. ___HCl + ___Na(OH)  ___H(OH) +___NaCl
H –2
Cl – 1
Na – 1
O–1
H–2
Cl – 1
Na – 1
O–1
 When equations do not have the same number of each
atom as reactants and products, they must be
“balanced.”
Procedure for Balancing Equations
1.
Count the number of each type of atom on each side of the
equation, saving Hydrogen, Oxygen and any element by itself
for last.
2. Change coefficients to change the number of each atom until
the same number is present on each side of the equation. Do
not insert numbers in the middle of a formula or change
the subscript in a formula.
3. Repeat for each successive type of atom until all are balanced.
Tip: If you reach a situation where an odd number of atoms exists on one side of
the arrow and an even number on the other. Double the number of odd atoms
and then finish your balancing. *
How to Balance….Not!

Aluminum reacts with Oxygen to form Aluminum Oxide

Do not change the subscripts in the compound formulas.

Do not place numbers in the middle of a formula.

If you use fractions in the equation, don’t leave them.

Correct equation would be:
___Al + ___O2 ---> ___Al2O3
_2_Al + ___O2 ---> ___Al2O2
_2_Al + _3_O2 ---> ___Al22O3
_2_Al + 1.5 O2 ---> ___Al2O3
_4_Al + _3_O2 ---> _2_Al2O3
*
Determining Mole Ratios
 The balanced equation gives the ratio of Moles of reactants
and products involved in the chemical equation (i.e recipe).
 To determine the mass of a reactant or product involved,
simply multiply the number of Moles times the molecular
weight/atomic mass of the reactant or product.
 Example:
3H2 + _N2  2NH3
The Mole Ratio is 3H2 : 1N2 : 2NH3 or 3:1:2
The Atomic Weights are 3x (1.008 x2) ; 1x (14.007 x2) ; and 2x
(14.007 +1.008x3)
So, 6.048 + 28.014 = 34.062 ; the Law of Conservation of Mass is
observed. *
Some Quick Practice
___KCl + ___MgO  ___K2O + ___MgCl2
Balanced Equation: 2KCl + MgO  K2O + MgCl2
Mole Ratios: 2:1:1:1
__NaNO3 + __Al2O3  __Al(NO3)3 +
__Na2O
Balanced Equation: 6NaNO3 + Al2O3  2Al(NO3)3 + 3Na2O
Mole Rations: 6:1:2:3
*
Balancing Equations
Homework
In your book, do the assigned work
on a single sheet of paper. Be sure
to show all work.
 p.166 #1-5
 p.168 #1-5