Download Conservation of mass

Name____________________________
Conservation of Mass Reading Guide
Page 78: During the 1780s the French chemist Antoine _________________________ showed that
_________________________ can never be __________________________ or ________________________.
Page 79: What does the Law of Conservation of Mass state?
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Page 80: Chemical ____________________________ can be described by chemical
______________________.
Chemical _________________________ represent how ____________ are rearranged in a chemical
reaction.
When you write a chemical equation, the ________________________ go on the left of the arrow and
the ___________________________ go on the right.
CH4 + 2O2  CO2 + 2H2O
Remember from a previous lesson that this is an example of a combustion reaction. CH4 is methane; O2 is oxygen gas; CO2 is carbon dioxide; H2O is water)
List the 2 reactants in this reaction: ________________________________
List the 2 products in this reaction: ________________________________
The coefficients (big numbers in front of chemical formulas) show how many molecules are present in a
reaction and the subscripts (small numbers after element symbols) show how many atoms of that element
are present in each molecule (but only for the element directly in front of the subscript). If there is no
number present, it is understood to be one.
Examples: 2H2O
CH4
-This shows 2 molecules of water. Each one has 2 atoms of hydrogen and one atom of oxygen
-This shows 1 molecule of methane. The molecule has 1 atom of carbon and 4 atoms of hydrogen
The get the total number of atoms of a specific element present on one side of the reaction, multiply the
coefficient by the subscript and then if the element is listed more than once, add those numbers together.
In this example ONE molecule of methane (CH4) and TWO molecules of oxygen gas (O2) react to form ONE molecule of carbon
dioxide (CO2) and TWO molecules of water (H2O).
One the reactants side (left) we have 1 atom of carbon, 4 atoms of hydrogen and 4 atoms of oxygen (2 molecules that each have 2
atoms of oxygen: 2x2=4). On the products side we have 1 atom of carbon, 4 atoms of hydrogen (2 molecules of water that each
have 2 atoms of hydrogen: 2x2=4), and 4 atoms of oxygen (2 atoms in the carbon dioxide plus 1 atom in each of the 2 molecules of
water). This shows that mass has been conserved. We have the same amount of each type of atom on each side of the chemical
reaction. Every chemical equation should reflect this same thing.
How many molecules of H2 are there?_______
How many molecules of O2 are there?________
How many molecules of H2O are there?________
In one molecule of H2O, how many hydrogen atoms are there? ________
In one molecule of H2O, how many oxygen atoms are there? _____
Element
Total number of atoms present on
reactant side
Total number of atoms present on
product side
Oxygen (O)
Hydrogen (H)
Does this equation show that mass has been conserved (do you have the same total number of each atom in the
reactants and in the products)? ___________________________________________________________
6CO2 + 6H2O  C6H12O6 + 6O2
This is the chemical equation for photosynthesis. CO2 is carbon dioxide; H2O is water; C6H12O6 is glucose; O2 is oxygen gas)
How many molecules of carbon dioxide are present?______
How many molecules of water are present? ______
How many molecules of glucose are present? ______
How many molecules of oxygen gas are present? ______
Element
Total number of atoms present on
reactant side
Total number of atoms present on
product side
Carbon (C)
Oxygen (O)
Hydrogen (H)
Does this equation show that mass has been conserved (do you have the same total number of each atom in the
reactants and in the products)? ___________________________________________________________
3Fe + 4H2O  4H2 + Fe3O4
Element
Total number of atoms
present on reactant side
Total number of atoms
present on product side
Fe
H
O
Does this equation show a conservation of mass (same number of atoms) on both sides? _____
4Al + 3O2  2Al2O3
Element
Total number of atoms
present on reactant side
Total number of atoms
present on product side
Al
O
Does this equation show a conservation of mass (same number of atoms) on both sides? _____