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Law of Conservation of Mass
Law of Conservation of Mass
• Think about the following question:
– If you burned a log in the fireplace,
would the mass of the products (smoke,
ashes, etc.) be the same as the
reactants (the wood)?
Law of Conservation of Mass
• Yes!
• In a chemical reaction, the total mass of
the reactants is always equal to the total
mass of the products
Law of Conservation of Mass
• Example: Burning of Methane
Methane + Oxygen → Water + Carbon dioxide
CH4 + O2 → H2O + CO2
Law of Conservation of Mass
• CH4 + O2 → H2O + CO2
• 4 Hydrogen atoms on the left hand side
(reactants); only 2 on the right side (products)
• Where did they go?
• Atoms cannot be created or destroyed, just
rearranged in a chemical reaction
• NEED TO BALANCE THE EQUATION!
Law of Conservation of Mass
CH4 + 2 O2 → 2 H2O + CO2
• The 2 means that there are 2 oxygen and
water molecules
• Now there are equal numbers of atoms on
both sides of the reaction