Conservation of Matter Notes
Chemical Reactions
• Happen all of the time
• Happen naturally or can be man made
• Can be physical or chemical
Law of Conservation of Matter
• Matter cannot be created or destroyed!
• The total amount of matter remains constant
• Even though the matter may change from one
form to another, the same number of atoms exists
before and after the change takes place!
• The mass of the reactants must equal the mass of
the products.
Evidence- How do we know the law is
true?
• The elements on the reactant side = the
elements on the products
• The # of each element on the reactant side =
the # of each element on the product side
• The mass of the reactants = the mass of the
products
Let’s Do the Math!
Counting Atoms
Writing Compounds
• Coefficient
– Number before the element/compound
– Tells you how many of the element/compound
there are
– Applies to everything after the coefficient up until
the + or →
• Example: 2H2O = The 2 coefficient is distributed to the
H2 and the O
– Total = 4 Hydrogen (2 x 2 = 4) and 2 Oxygen (2 x 1 = 2)
Writing Compounds
• Subscript
– Number after the element - lower right side
– Tells you how many atoms of that element there
are
– Example: H2O → The 2 subscript only applies to
the Hydrogen and not the Oxygen.
– Subscripts and parenthesis
• If a subscript is after a parenthesis “( )” then it applies
to everything inside of it
• Example: (H2O)2 = The 2 subscript applies to the H2O
– Total = 4 Hydrogen (2 x 2 = 4) and 2 Oxygen (2 x 1 = 2)
Counting Atoms in a Compound
Practice
– CaCO3
• Ca = 1
•C=1
•O=3
– C9H8O4
•C=9
•H=8
•O=4
– Mg(OH)2
• Mg = 1
•O=2
•H=2
Counting Atoms in a Compound
Practice
– 2FeS2
• Fe = 2
•S = 4
– H2O + O2
•H = 2
• O = 1+ 2 = 3
– 2C7H5(NO2)3
• C = 14
• H = 10
•N = 3
•O = 6
Balancing Equations Notes
Why do we need to be balanced?
• All atoms that are on the reactant side are
also on the product side
o Remember the Conservation of Mass Law
Steps to balance equations
1.
2.
3.
4.
5.
Count the # of atoms on each side
Add Coefficients where necessary
NEVER CHANGE OR ADD SUBSCRIPTS!
Recount the # of atoms on each side
Continue adding coefficients until the number of
atoms on each side are equal.
6. Reduce the coefficient to the lowest terms
(Hint: Start with 2 and see where it gets you!)
Hints to remember
• Order for Balancing
•MI NOH → (Me Know)
• Metals
• Ions
• Non-Metals
• Oxygen
• Hydrogen
•Balance Oxygen and Hydrogen LAST!
LET’S PRACTICE!
• Step 1: Count the # of atoms of each side
LET’S PRACTICE!
• Step 2: Add Coefficients where necessary
LET’S PRACTICE!
Step 3: Recount the # of atoms on each side
LET’S PRACTICE!
• Step 4: Continue adding coefficients until the
number of atoms on each side are equal.
LET’S PRACTICE MORE!
___ Na + ___ Cl2 →___ NaCl
_2_ Na + ___ Cl2 →_2_ NaCl
AND MORE!
AND MORE! ANSWERS
• ___CH4 + 2 O2
• 2 Li + 2 HNO3 →
→
___CO2 + 2 H2O
2 LiNO3 + ___ H2
• 2 AgNO3 + ___Cu → ___ Cu(NO3)2 + 2 Ag
• 4 Al + 3O2
→ 2 Al2O3