Download 4-3 Conservation of Matter

BSCS Inquiry Science 9
Ch. 2 Material World
Name:
Period:
Date:
Elaborate: Reacting to Density – Conservation of Matter
Read the paragraphs on p. 86
Law of Conservation of Matter – matter can neither be created nor destroyed, but can be changed from
one form to another.
What does this mean? It means that the number of atoms present before the reaction (reactants) must
be equal to the number of atoms after the reaction (products).
Reactions
contain two parts
Reactants
Products
yields
Substances that are
being mixed
Substances that are new;
formed during the reaction
The reactants are always on the left side of the equation, and the products are always on the right.
A chemical equation is a way of describing a chemical reaction using chemical formulas.
3H2O
Symbol for Hydrogen ______
Symbol for Oxygen ______
Subscript
______
Coefficient
______
Chemical bonds hold atoms close to each other to form molecules.
Hydrogen
Oxygen
Nitrogen
# of chemical bonds
1
2
3
Carbon
4
(HONC)
Activity - Marshmallows
The natural gas, methane (CH4), when ignited combines with oxygen (O2) gas in the air to produce
carbon dioxide (CO2) and water (H2O). CH4 + O2  CO2 + H2O (unbalanced reaction)
1. Build physical models of the reactant and product molecules for the combustion of methane.
The colored marshmallows represent types of atoms.
Carbon = black
Hydrogen = white
Oxygen = red
2. Consider with your team how you could use a balance to help you model conservation of matter with
the molecules you constructed.
2a. Sketch each molecule below.
2b. Take into consideration the meaning of the arrow in a chemical reaction, which models/atoms
should be to the left of the arrow and which should be to the right?
Revised: 5/6/2017
BSCS Inquiry Science 9
Ch. 2 Material World
2c. Draw & label each atom with its proper symbol and state whether it is part of a reactant or product.
CH4
O2
CO2
H2O
(reactant or product)
(reactant or product)
(reactant or product)
(reactant or product)
+
+
Reactant
Product
2d. Build more of any molecule required in order to demonstrate conservation of matter (balance) at the
atomic level. The type and number of atoms must also be the same on both sides of the yield arrow.
Draw those molecules above.
3. Using the chemical formula for each of the substances, plus signs, and an arrow, write the balanced
chemical equation for this reaction below. Note: You CANNOT add or change a subscript. The only
place you can add numbers are in front of the molecules. These numbers are called coefficients. A
coefficient represents the number of molecules that are present. (2H2O means two molecules of water)
Balanced Chemical Equation:
+
+
Stop and Think p. 87
1. Which half of the reaction, reactant or product, had a greater mass when you constructed only 1
molecule of each methane, oxygen, carbon dioxide, and water? Explain why, using correct symbols
for each atom and the law of conservation of matter.
2. Which molecules did you have to build more of in order to show conservation of matter? Explain how
you selected which molecules and how many.
Practice Balancing Equations
1.
H2
2.
H2O2
+
O2
H 2O
H 2O
+
O2
Revised: 5/6/2017
BSCS Inquiry Science 9
3.
N2
+
Ch. 2 Material World
H2
NH3
4.
P4
+
O2
5.
C
+
H2
P4O10
CH4
Revised: 5/6/2017