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!
• Example: Tin Fluoride
– Tin + hydrogen fluoride → tin fluoride + hydrogen
2.0
1g
156
.71
• What’s the total mass of the reactants?
158.72
• So what should the mass of the products be?
158.72
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
oRemember 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!
• ___ CH4 + ___ O2 → ___ CO2 + ___ H2O
• ___ Li + ___ HNO3 → ___ LiNO3 + ___ H2
•
___ AgNO3+ ___ Cu → ___ Cu(NO3)2 + ___ Ag
• ___ Al + ___ O2 → ___ Al2O3
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