1. Law of Conservation of Mass Lavoisier (1743-1794)
Coal is completely burned
100 g
100 g
START
END
What do you observe?

2. Law of Conservation of Mass Lavoisier (1743-1794)
Coal is completely burned
100 g
100 g
Weight of jar & its contents remains the same. Mass is conserved
In a chemical reaction, matter is neither created nor destroyed, it is transformed into something else.

3. balanced mass Since matter can not be created or
destroyed, chemical reactions must be
__________ in terms of _________.
balanced
mass
The amount of mass you start with must
equal to the mass of the products:
Reactants  Products
100g total =
100g total

4. The mass on both sides of the arrow must be equal.
According to the law of conservation of mass, how much zinc was present in the zinc carbonate? + = +
256g
256g
REMEMBER !!!
The mass on both sides of the arrow must be equal.
A 40 g B 88 g C 104 g D 256 g
ANSWER: = 104g of Zn

5. CuCO3(s)  CuO(s) + CO2(g) 123.6 g 79.6 g ? g 44.0 g
According to the law of conservation of mass, how much carbon dioxide was present in the copper (II) carbonate?
CuCO3(s)  CuO(s) + CO2(g)
123.6 g
79.6 g
? g +
44.0 g
123.6g
123.6g
What are the reactants?
CuCO3
123.6 g
What is the mass of reactants?
Mass?
CuO & CO2
What are the products?
What is the mass of products?
79.6 g + CO2
Answer: – 79.6 = 44.0g of CO2

6. For the Last Two Examples
You can set every Chemical Equation up like an Algebraic Equation and solve it for the variable. For instance this equation,
can be written algebraically using the masses given on the previous slide like below. Now you only have to solve for x!
123.6 [g] = 79.6 [g] x
CuCO3(s)  CuO(s) + CO2(g)