Download CLASS NOTES- Balancing Chemical Equations.pptx

BALANCING CHEMICAL
REACTIONS
Honors Chemistry
Balancing Chemical Equations
Learners will know…
•  The Law of Conservation of Mass as it relates to chemical
changes of substances
•  The parts of a chemical reaction
Learners will be able to…
•  Write and balance chemical equations
•  Perform stoichiometry calculations
The Law of Conservation of Mass
•  Matter is neither created nor destroyed.
•  In chemical reactions, the amount of particles in the
reactants is equal to the amount of particles in the
products.
Chemical Reactions
• Chemical reactions involve changes
in the chemical composition of matter
• Creates new materials with new
properties
• AMOUNT of matter does not change!
• Chemical equations describe a
chemical reaction
• Written similar to a mathematical
equation/is like a ‘RECIPE’
Basic Chemical Equations
•  Reactants = Atoms or compounds that are changed in a
chemical reaction (LEFT SIDE)
•  Products = Atoms or compounds that are generated as a
result of a chemical reaction (RIGHT SIDE)
Parts of a Chemical Equation
Coeffecients and Subscripts
•  SUBSCRIPTS = how many atoms or ions within a
compound
•  COEFFECIENTS = how many moles or formula units
Rules for Chemical Equations
•  Because of Law of Conservation of Mass, chemical
equations MUST BE BALANCED
•  BALANCED = same number of each kind of atom on both
sides (reactants and products)
Rules for Chemical Equations
•  The TOTAL number of any given atom is equal to the
COEFFECIENT x SUBSCRIPT
H=2x2=
4
Rules for Chemical Equations
•  You MAY change the COEFFECIENTS
•  You MAY NOT change the SUBSCRIPTS
WHY NOT?
Changing the subscripts changes the
compound
A look at balanced chemical reactions
STEPS for Balancing Chemical Equations
There are FOUR basic steps
1. Write the correct formula for the reactants
and the products
~ DO NOT TRY TO BALANCE IT YET! You
must write the correct formulas first.
**And most importantly, once you write
them correctly DO NOT CHANGE THE
FORMULAS!
2. Find the number of atoms for each
element on the left side
~ Compare those against the number of
the atoms of the same element on the
right side.
STEPS for Balancing Chemical Equations
3. Determine where to place coefficients in front of
formulas
~ Left side must have same number of atoms as
the right side for EACH element in order to
balance the equation
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)
! Tips and Tricks !
•  Take one element at a time, working left to
VIDEO:
right except for H and O
•  Try metals then nonmetals
•  Save H for next to last, and O until last.
https://
www.youtube.com/
watch?
v=UGf60kq_ZDI
•  IF everything balances except for O (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
USE THESE STEPS!
1.  Metals
2.  Nonmetals
3.  Hydrogen (H)
4.  Oxygen (O)
•  If Oxygen doesn’t balance, double all coeffecients!
EXAMPLE
You try it!
•  Balance the following chemical equation:
__C + __S8 à __CS2
TUTORIAL (PHET)
•  Use the simulation on this site to practice and re-learn the
concepts
•  LINK:
http://phet.colorado.edu/blog/2014/09/08/new-html5-balancing-chemicalequations-simulation/
•  DIRECT LINK:
http://phet.colorado.edu/sims/html/balancing-chemical-equations/latest/
balancing-chemical-equations_en.html
MOLE RATIOS