Law of Conservation of Mass

French chemist Antoine Lavoiser used equipment
designed to trap gases and measure mass

LAW OF CONSERVATION OF MASS- in any given
chemical reaction, the total mass of the reactants
equals the total mass of the products

During a chemical reaction, the atoms in reactant
molecules are rearranged to form products

All the atoms that existed in the reactants are still
present in the products

Atoms cannot be created or destroyed
Date:
Homework
1) The idea that gases have mass can be difficult to accept. Why do you think that is?
2) a) State the Law of Conservation of Mass
b) Explain the Law of Conservation of Mass
3) Are the following situations exceptions to the law of conservation of mass? Justify your answer in each case.
a) The mass of a hamburger decreases as it is barbecued.
b) A tree’s mass is continually increasing as the tree grows.
c) The mass of a copper penny increases if it is heated in a Bunsen burner flame.
d) You are often lighter in the morning than you were when you went to bed.
4) You might have noticed new copper roofs turn green over time. This occurs because copper reacts with
substances in the air to form a hard, protective coating. Will the mass of the new copper roof increase or
decrease over time? Explain. Does this prediction violate the law of conservation of mass?
5) Design an experiment involving the reaction of vinegar and baking soda to test the law of conservation of mass.
6) A 20g sample of compound A is mixed with 45g of compound B. A chemical reaction occurs in which a gas is
produced. Once the reaction is complete, the final mixture has a mass of 55g.
a) What is the mass of the gas?
b) What assumption did you make in a)?
7) Soon after learning about the work of Lavoiser, John Dalton proposed that atoms are never created or destroyed
in chemical reactions, only rearranged. Explain how this statement applies to the Law of Conservation of Mass.
Homework- ANSWERS
1) The idea that gases have mass can be difficult to accept. Why do you think that is?
because you can’t see them
2) a) State the Law of Conservation of Mass
in any given chemical reaction, the total mass of the reactants equals the total mass of the products
b) Explain the Law of Conservation of Mass
no mass is lost or gained during a chemical reaction, mass before=mass after
3) Are the following situations exceptions to the law of conservation of mass? Justify your answer in each case.
a) The mass of a hamburger decreases as it is barbecued. fat in the meat melts and drips out of the hamburger
into the collection tray of the BBQ
b) A tree’s mass is continually increasing as the tree grows. the tree is growing, creating additional mass by
taking in nutrients (mass) from its environment and turning it into cells, tissues, etc.
c) The mass of a copper penny increases if it is heated in a Bunsen burner flame. it is reacting with oxygen in the
air, the extra oxygen adds mass
d) You are often lighter in the morning than you were when you went to bed. through out the night, you are
losing water from your body as sweat
4) You might have noticed new copper roofs turn green over time. This occurs because copper reacts with
substances in the air to form a hard, protective coating. Will the mass of the new copper roof increase or
decrease over time? Explain. Does this prediction violate the law of conservation of mass?
increase, the copper is reacting with water and oxygen, mass is being added so it doesn’t violate the law of
conservation of mass
5) Design an experiment involving the reaction of vinegar and baking soda to test the law of conservation of mass.
6) A 20g sample of compound A is mixed with 45g of compound B. A chemical reaction occurs in which a gas is
produced. Once the reaction is complete, the final mixture has a mass of 55g.
a) What is the mass of the gas? 10g
b) What assumption did you make in a)? the mass of the gas equals the missing mass after the reaction
7) Soon after learning about the work of Lavoiser, John Dalton proposed that atoms are never created or destroyed
in chemical reactions, only rearranged. Explain how this statement applies to the Law of Conservation of Mass.
atoms have mass, if mass is not lost during a reaction, then, the atoms must still be present but be in different
arrangements since the products are different substances