is the mass of the cake different than the mass of the
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Is the mass of the cake different than the mass of the ingredients?
Does mass change during a chemical reaction?
Topic 5: Conservation of Mass
In this lesson you will learn
❑ what the Law of Conservation of Mass is
❑ how to balance chemical equations so they obey the Law of Conservation of Mass
Experiment 1
Experiment 2
• The Law of Conservation of Mass states that matter cannot be created or destroyed• If you begin with 10 g of reactants, you will end with 10 g of
products.
• What is the total mass of the reactants? ______
• What is the total mass of the products? ______
Oxygen
Practice
• What will be the mass of water?
15 g 20 g 10 g ?
Count the number of atoms of each element in the reactants and products. Does this chemical equation obey the law?
Balancing Chemical Equations
• To write chemical equations that obey the Law of Conservation of Mass, we must balance them so that the atoms are equal on both sides.
• To do this, we add copies of reactants and products as needed until the number each element is the same.
EXAMPLE 1
____ Li(s) + _____O2(g)→ ____ Li2O(g)
Count atoms:
Draw:
EXAMPLE 2
____Fe2O3(s)→ ____ Fe(s) + ___O2(g)
Count atoms:
Draw:
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