5 3 lecture
DESCRIPTION
TRANSCRIPT
5.3 Balancing Chemical Equations
Pages 161 - 165
Goal 1
Describe and balance chemical equations
• Word equation
Methane + Oxygen Carbon dioxide + Water
Reactants Products
• Chemical Equations– Balanced to show conservation of mass– #Atoms per element go in = # Atoms per
element that come out
• Chemical equationsUse chemical formulas and coefficients
CH4 + 2O2 CO2 + 2H2O
• Coefficients used to show– # of molecules/compounds – # of moles– Multiply subscripts by coefficients to
determine the # of atoms
CH4 + 2O2 CO2 + 2H2O
• C =
• H =
• O =
• C =
• H =
• O =
CH4 + 2O2 CO2 + 2H2O
# of atoms on left MUST = # of atoms on right
Is this equation balanced?
CH4 + 2O2 CO2 + 2H2O
Yes! It’s balanced
• H =
• O =
• H =
• O =
H2 + O2 H2O
# of atoms on left MUST = # of atoms on right
Is this equation balanced?
Uh-Oh!
• H =
• O =
• H =
• O =
H2 + O2 H2O
# of atoms on left MUST = # of atoms on right
How can we balance it?
• Rules for balancing chemical equations
– 1. Only change coefficients
– 2. Never never never ever change a subscript
– 3. Multiply subscripts by coefficients
– 4. Compounds FIRST
– 5. Elements LAST
• H =
• O =
• H =
• O =
__ H2 + __ O2 __ H2O
# of atoms on left MUST = # of atoms on right
Try it…
• H = 4 atoms
• O = 2 atoms
• H = 4 atoms
• O = 2 atoms
_2_ H2 + __ O2 _2_ H2O
# of atoms on left MUST = # of atoms on right
Try it…
• Mg =
• O =
• Mg =
• O =
__ Mg + __ O2 __ MgO
# of atoms on left MUST = # of atoms on right
Let’s try it again…
• Mg = 2 atoms
• O = 2 atoms
• Mg = 2 atoms
• O = 2 atoms
_2_ Mg + __ O2 _2_ MgO
# of atoms on left MUST = # of atoms on right
How did you do?
• C =
• H =
• C =
• H =
__ CH4 __ C3H8 + __ H2
# of atoms on left MUST = # of atoms on right
Let’s try it one more time…
• C =
• H =
• C =
• H =
_3_ CH4 __ C3H8 + _2_ H2
# of atoms on left MUST = # of atoms on right
How did you do?