Chemistry Journal
4.01 Conservation of Mass
Driving Question: How does a balanced chemical equation demonstrate conservation of
mass?
Key Ideas and Terms
Notes
FQ: What are the components of a chemical equation?
A chemical reaction starts with a Reactant, product
______ and ends with a ______.
Video: Chemical Reactions (1)

What factors are necessary
for a chemical change to take
place?
If two or more elements or chemical compounds come into
contact with one another and there is enough energy present, a
chemical change may take place.

How are changes of state
different from chemical
change?
Remember that a physical change is a change in properties such as
texture, shape, or state, while a chemical change represents the
formation of a new substance after atoms are rearranged in a
chemical reaction.
What is a chemical equation, and
how do scientists use these
equations to represent chemical
reactions?
a representation, using formulas and symbols, of a chemical
reaction
Examine the equation below.
Explain what the subscripts of
the reactants and products
represent.
Just as you are reading this sentence, you read a chemical
equation from left to right. The reacting substances are to the
left of an arrow (represented with letters AB and C), and the
newly formed products are to the right of an arrow (represented
by the letters A and BC). These reactants and products are
usually represented in chemical equations by their chemical
formulas. The phases of each substance can be shown in
subscripts: (s) for solid, (l) for liquid, and (g) for gas.
Compounds that have been dissolved in water to form a
solution are given the subscript (aq) for aqueous solution.
AB(s) + C(l) → A(g) + BC(aq)
They allow us to describe the chemical reaction without having
to write a long paragraph about the ratios of reactants and
products in the reaction.
FQ: How does a balanced chemical equation demonstrate conservation of mass?
Describe the law of conservation
of mass.
Explain why the chemical
formula below is "balanced."
the law that explains that mass cannot be created or destroyed
within a closed system
by having equal numbers of each element on both sides
2Cu + O2 → 2CuO
Video: Chemical Reactions (2)

In a chemical reaction, atoms
cannot be _______ or
_________, just rearranged.

Explain how the equation
that makes water in the video
represents a "balanced"
equation.
to fix the equation, another hydrogen atom is added to create 2
water molecules

How do balanced equations
demonstrate the conservation
of mass?
matter cannot be create or destroyed in a chemical reaction, the
mass of all the reactants will always add up to total mass of
products
created or destroyed
FQ: How does the law of conservation of mass apply to chemical reactions?
How does a balanced chemical
equation demonstrate
conservation of mass?
demonstrates the conservation of mass by showing equal ratios
of compounds in reactants and the product
Interactive: Law of Conservation of Mass

In trial 1 of the vinegarbaking soda reaction, how
did the masses of reactants
and products compare?
the original mass of vinegar and baking soda was 782g and it's
product was 780g

In trial 2 of the vinegarbaking soda reaction, how
did the masses of reactants
and products compare?
the weight before and after the reaction is 784g

Why was the result different
in trial 2 compared to trial 1?
since the balloon trapped some of the product from escaping, the
product was the same weight

Did this reaction demonstrate
it explains that even in different states, the law of conservation
the law of conservation of
mass? Explain why or why
not.
How does the law of
conservation of mass also apply
to physical changes?
still holds true. with all of the elements together in the 2nd trial,
the weight was that same.
substances can change form, but the total mass remains the
same
FQ: How are coefficients used to balance an equation?
What do coefficients in a
chemical reaction indicate?
the number of molecules or formula units that take part in
chemical reaction
How do chemists use
coefficients to satisfy the law of
conservation of mass?
add coefficients to reactants and products in a chemical equation
until same number of each atom on both sides of equation
Why can we only use
coefficients in front of a formula
to balance a chemical equation?
an observed chemical reaction, so formulas cannot be changed
changing subscripts changes identity of the compounds
What happens to the chemical
formula if you change a subscript
instead of a coefficient?
Identify the number of atoms of
each element in the reactants and
the products in the following
equation.
carbon: 1 (reactants) 1 (products)
oxygen: 2 (reactants) 3 (products)
hydrogen: 4 (reactants) 2 (products)
CH4(g)+ O2(g) → CO2(g) + H2O(g)
FQ: How do you balance a chemical equation?
Jot down six tips to help you
make sure an equation is
balanced.
1: count number of atoms for each element
2: adding number in front of compound affects number of each
element in compound
3: element found in more than 1 compound in same side of
equation
4: may have to change coefficient more than once
5: polyatomic ion appears both sides of equation, balance ion as
single unit
6: double check every element is balanced on both sides
Describe the steps needed to
balance the equation.
placing 2 on product Fe gives 2 atoms of iron on both sides of
equation.
placing 3 on H2O balances oxygen, but also changes amount of
Fe2O3 + H2 → Fe + H2O
hydrogen atoms from 2 to 6.
place coefficient 3 o H2 to rebalance hydrogen atoms.
check elements again: 2 iron, 3 oxygen, 6 hydrogen on each side
Be sure to record any extra helpful notes, vocabulary terms, and practice sample problems.