1. Chemical Reactions and Conservation of Mass

2. A chemical reaction can be represented by a WORD EQUATION.
Example:
Hydrogen gas + Oxygen gas Water
Products:
The ending materials
Reactants:
the starting materials

3. Test Reaction: Question: Procedure:.
How will the mass of the reactants in a chemical reaction compare with the mass of products?
Test Reaction:
Iron (III) nitrate + sodium  iron (III) hydroxide + sodium
hydroxide nitrate
DEMONSRATION: Allow chemicals to react in a CLOSED container
1. Place reactants in CLOSED (sealed) flask.
2. Measure mass before reacting.
3. Measure mass after reacting.
Procedure:.
Why is it important that the container be closed?
So no materials can escape or be added to the system!

4. Summary: The mass before and after the reaction is the same.
Prediction and Observation:
Initial Mass before reaction: (g)
Predicted Mass after reaction: (g)
Measured Mass after reaction: (g)
Explanation:
Summary: The mass before and after the reaction is the same.
This is because the number of atoms stays the same.
The atoms are rearranged but are NOT created or
destroyed!

5. Law of Conservation of Mass
In a chemical reaction, the mass of the reactants is equal to the mass of the products.
Applying Conservation of Mass : How many grams of oxygen reacts with 40 g of calcium oxide to produce 100 g of calcium oxide?
Calcium + Oxygen → Calcium Oxide
40 g ? g
Ans: Mass of oxygen = 100 g – 40 g = 60 g

6. A CHEMICAL EQUATION uses chemical symbols to represent a reaction:
Hydrogen gas + Oxygen gas Water
H O2  H2O
This is called a skeleton equation- the number of atoms on either side are not balanced!

7. H2 + O2  H2O 2 2 2 2 4 4 2 2 1 To balance the equation, we need
to add balancing coefficients in front of
the terms!
H O2  H2O 2 2
Atom
Left Side
Right Side
Balanced ? H O 2 2 4 4 2 2 1