1. GO 2 Describe and interpret patterns in chemical reactions
2-2 Conservation of Mass

2. What impact do chemical reactions have on mass?
Guided Question
What impact do chemical reactions have on mass?

3. 2-2: Conservation of Mass
In GO 2-1 we learned that matter can be re- organized in a chemical reaction to form new compounds.
For example:
REACTANTS PRODUCTS
Something does NOT happen in that rearrangement though:
MASS DOES NOT DISAPPEAR
The total mass of the reactants EQUALS the total mass of the products

4. Prove it Antoine! Law of Conservation of Mass
Antoine Lavoisier
Weighed a sealed glass vial with tin inside, then heated it until it turned to a white powder
Weighing the tin after the white powder formed, he found there was no mass lost!
Lavoisier’s experiment showed that mass cannot be gained or lost in a chemical reaction

5. What’s the difference between the Experiment and the Real World?
Lavoisier created a closed system for his experiment. Closed system - no matter can enter/leave the system only energy In the real world, we have an open system which do not allow the Law of Conservation of Mass to be SHOWN Open system - there is exchange of matter and energy with surroundings

6. FYI: isolated system – neither matter nor energy can enter/leave the system
Ex. Burning wood is a high energy release procedure.
If wood was burned in a lab under controlled conditions, a closed system allows us to measure no change in mass.
But when burning wood in an open system, mass is lost to the environment; once gone, that mass cannot be measured.

7. What does this have to do with Chemical Equations?
When we write chemical equations, there must be an equal number of each element on both sides of the reaction arrow
2A + 3B A2B3
If there is a difference between the two sides, mass is not being conserved and the reaction must be fixed
we call this “balancing the reaction”