Transcript Chemical Equations and Reactions

Chemical Equations & Reactions
Chemical Equation


A chemical equation is the
symbolic representation of
a chemical reaction in the
form of symbols.
You list the reactants
(elements that combine
together) on the left side
and the product (the final
combination) on the right.
Types of Equations



Skeleton equation: summarizes the reaction in symbol
form.
Ex: H2 + O2 → H2O
Balanced Chemical equation: Includes coefficients to
represent equal number of atoms on both sides of the
equation
Ex: 2H2 + O2 → 2H2O
Word equation: All elements are written out in words to
describe the reaction
Ex. Hydrogen reacts with oxygen to produce water
Writing Chemical Equations
Reactants on left
side of the arrow
Products on right
side of the arrow
hydrogen + oxygen  water
Plus sign means
“reacts with”
Arrow means
“produce”
Diatomic Molecules
 Diatomic
molecules are composed of
two of the same atom.
 In nature the following atoms only
occur naturally as diatomic
molecules: H O Br F I N Cl
 Ex: H2, Cl2, Br2…
Law of Conservation of Mass

States that the mass of the reactants in
chemical equations must equal the mass of
the products.

Remember: “atoms cannot be created or
destroyed” so we must have the same number
of atoms of each type in the reactants as we do
in the products.
Counting Atoms

A large number in front will apply to each atom
 2OH means 2 O and 2 H
 2KCl means…

Subscript numbers only apply to the atom it
touches
 H2O means 2 H and 1 O
 CaCl2 means…
Counting Atoms

Multiplication is used when two numbers are
present
 2H2O means 4 H and 2 O
 3SrCl2 means…

When brackets are used, a number outside of
brackets will apply to all atoms inside
 Ca(OH)2 means 1 Ca, 2 O and 2 H
 2Mg(NO3)2 means…
Balancing Equations

Add coefficients to make sure that there are
the same number of atoms of each type on
both sides.
Tricks for Balancing

1.
2.
3.
4.
5.
6.
The ONLY number you can change is the number in front
of the formula – the coefficient!!!
Balance H
Balance Metals
Balance Non-Metals
Balance polyatomic ions
Balance O at the end
CHECK to make sure ALL atoms are balanced at the
end !!
So what does this look like?
__C + __S8 → __ CS2
C
C
C
C
S8
CS2
CS2
CS2
CS2
Let’s Try it Again!
__H2+ __O2 → __ H2O
H2
H2
O2
H 2O
H2O
A little more complicated!
__SF4 + __H2O → __ SO2 + __ HF
SF4
H2O
H2O
SO2
HF
HF
HF
HF
Try Some!
1.
__Na + __O2 → __ Na2O
2.
__ C+ __ O2→ __ CO
3.
__ Al + __ H2SO4 → __ Al2(SO4)3 + __H2
4.
__ C2H6 + __ O2 → __ CO2 + __H2O
Try Some!
1.
4 Na + 1 O2 → 2 Na2O
2.
2 C+ 1 O2→ 2 CO
3.
2 Al + 3 H2SO4 → 1 Al2(SO4)3 + 3 H2
4.
2 C2H6 + 7 O2 → 4 CO2 + 6 H2O