WARM – UP: A-day




Update your Table of Contents
Write your homework – leave it to be stamped
Get your Adopt-An-Element Baby Book AND
get ready to grade it!
We will grade your tests next class!
Date
10/1010/11
Session
#
17
Activity
Page
#
Balancing Act Note Guide
27
Practice Equations – (hand copy into your notebook
from the slides!)
28
WARM – UP: B-day
Update your Table of Contents
 Write your homework – leave it to be
stamped
 Get something to grade your test!

Date
10/1010/11
Session
#
17
Activity
Page
#
Balancing Act Note Guide
27
Practice Equations – (hand copy into your notebook
from the slides!)
28
Physical & chemical changes can
change matter, BUT…THE BIG
QUESTION Is:
During those changes, is any
matter created or destroyed?
Law of Conservation of Mass (Matter)
Law of Conservation of Mass (Matter)Matter cannot be created or destroyed, it
can only change form
So where does the wood go?
Na
F
NaF
In other words, what
goes in, must come out!
Chemical Reactions
Reactants –
Elements
present at the
beginning of
a chemical
reaction
Product –
Compounds
formed by
a chemical
reaction
R
E
A
C
T
A
N
T
S
P
R
O
D
U
C
T
Na
F
NaF
The arrow indicates
that a chemical
reaction has occurred
Balancing Chemical Equations

Since matter can neither be created or
destroyed, the mass/amount of
reactants must always equal the
mass/amount of products
Balancing Chemical Equations

Before (Reactants)
Na
F

After (Product)
NaF
Na = 1
Na = 1
F=1
F=1
But What If It Doesn’t?
 STOP,

THINK, DISCUSS…
If you weigh your reactants before a chemical
reaction, and the products afterwards and
they DO NOT have the same mass before and
after what likely happened during the
chemical reaction? (Hint: Think about the
wood burning in the fireplace)
Dry Ice Demo
 As
you watch the dry ice demo
write ANY observations! (5 senses)
 Explain
how this demonstrates
The Law of Conservation of Mass!
Dry Ice Demo
Dry Ice = Solid Carbon Dioxide
 Freezing Point of Carbon
-108.4oF or -78oC
 Boiling Point of
-76oF or -57oC
 Formula:
CO2(s)
Dioxide =
Carbon Dioxide =
CO2(g)
Law of Conservation of Mass (Matter) Lab
Investigation Roles




Group Leader – Responsible for reading and making
sure the group is following directions accurately and
completing all parts of the lab
Supply Manager – gets and returns supplies and makes
sure they are clean -assists measurement technician in
calibrating the scale
Measurement Technician – gets and returns the scale
balance and is responsible for accurate mass
measurements
Data Discussion Technician – makes sure the group
records the mass data before and after the experiment,
AND has an explanation for BOTH THE TEACHER DEMO
AND STUDENT LAB
Law of Conservation of Mass (Matter) Lab
Investigation


Send your supply manager to get the lab kit
from the front counter and measurement
technician to get the scale balance from the
back counter
Group leader, read the directions carefully each
step of the way!!
◦ WARNING: YOUR BALLOON IS ALREADY FULL
OF BAKING SODA, DO NOT TIP IT INTO THE
GRADUATED CYLINDER ACCIDENTALLY!
Law of Conservation of Mass (Matter) Lab
Investigation Clean-Up






Balloons in the garbage
Rinse graduated cylinder thoroughly
Wipe up any spills
Put all items back into your lab kit & put them
on the front counter
Put scale balance back onto the back counter
Make sure every group member has
measurements and an explanation for BOTH
THE STUDENT LAB AND THE TEACHER DEMO –
WORK ON THE COMPARE & CONTRAST
TOGETHER!
Compare & Contrast
 Again,
the explanation should
state how this experiment
demonstrated the Law of
Conservation of Mass…BUT,
 What were the similarities and
differences between the
teacher demo and the student
mini lab?
Chemical formulas
for elements
Chemical formula
for new compound
2H2 + O2  2H2O
Coefficient
Subscripts
(Reactants)
Subscript
Coefficient
(Products)
What is that little number?
Subscript –
◦ Shows how many atoms of an
element are in a compound.
◦ When there is NO subscript there is
only 1 atom of that element.
O2
NaCl
NH4
K5N4C2
What is that big number in front?
Coefficient –
◦ The number of molecules
(compounds) involved in a chemical
reaction
H2
O2
H2
2 H2
O2
2
H2O
So the coefficient tells you the number of
molecules, but what about each atom?
 You must multiply…it is like the
distributive property in math!
3O2
2NH4
5H2O
2Li3F2
4NaCl
2K5N4C2
Rules for Balancing Chemical Equations
1. You CANNOT change subscripts, you can
ONLY change coefficients
2H2 + O2
2H2O
2. It does NOT have to look the same on both
sides, it only has to be balanced
3. You CANNOT split compounds to write in a
coefficient:
HCl
Rules to Balancing Chemical Equations
4. Only multiply through when it is a compound
because they have already bonded
2H + Cl
NO
2HCl
YES
5. If it is a capital letter, they are each a
separate element:
H, C, O
If it is a capital letter followed by a lower
case letter, it is all one element:
Cl, Li, Si
Steps for Balancing Chemical Equations


1. Divide the reactants from the products
with a line.
2. Write down the chemical symbol of each of
the elements on each side of the equation
2 H2 + O
2
2H2O
H=
H=
O=
O=
Steps to Balancing Chemical Equations


3. Using the coefficients and subscripts write
down the number of each element
4. If they are not balanced change the
coefficients using trial and error. You will have
to go back and forth between each side!
2 H2 + O
2
2H2O
H=4
H=4
O=2
O=2
Lets Practice
P + O2
P 4O6
Lets Practice
Na + O2
Na2O
Lets Practice
Al2O3
Al + O2
Lets Practice
Cl2 + KI
KCl + I2
WARM – UP: A-Day
Update your Table of Contents
 Write your homework – leave it to be
stamped
 Get something to grade your test with!

Date
10/14 10/15
Session
#
18
Activity
Page
#
Law of Conservation of Mass Note Guide
29
Balancing Equations Practice
30
WARM – UP: B-Day
Update your Table of Contents
 Write your homework – leave it to be
stamped
 Get your “Baby” out and we will grade
your Baby Book using the rubric on your
desk!

Date
10/14 10/15
Session
#
18
Activity
Page
#
Law of Conservation of Mass Note Guide
29
Balancing Equations Practice
30
Warm-Up Review
 Complete
the WarmUp/Review section at the top
of your note guide.
REVIEW
LAW
OF
CONSERVATION OF
MASS (MATTER)
Law of Conservation of Mass (Matter)
Law of Conservation of Mass (Matter)Matter cannot be created or destroyed, it
can only change form
In other words…
What goes in, must come out!
Law of Conservation of Mass (Matter)
Analyzing Reactions


Some chemical reactions are
ENDOTHERMIC = take “in” or absorb
energy
Some chemical reactions are
EXOTHERMIC = give “out” or produce
energy
How would you tell the difference?
Endothermic Reactions




An endothermic reaction takes “in” or absorbs
energy
Causes temperature around it to cool (will feel
cold)
They are forming a chemical bond which requires
energy to occur
EXAMPLE: Photosynthesis (needs energy from the
sun)
Exothermic Reactions




An exothermic reaction gives “out” or produces
energy (heat, light or sound)
Causes temperature around it to rise (feels
warm/hot)
They are breaking a chemical bond which
releases energy
EXAMPLE: cellular respiration (gives energy to
your cells)
Endo & Exo Lab Investigation Roles




Group Leader – Responsible for reading and
making sure the group is following directions
accurately and completing all parts of the lab
Supply Manager – gets and returns supplies
and makes sure they are clean
Data Discussion Technician – makes sure the
group records all observations and has an
explanation for BOTH investigations!
Speaker – Group member that must share your
explanation/conclusion with the class.
REVIEW
BALANCING
EQUATIONS…Please
get your Rules &
Steps for balancing
equations out!
Rules for Balancing Chemical Equations
1. You CANNOT change subscripts, ONLY
coefficients
2H2 + O2
2H2O
2. It does NOT have to look the same on both
sides, it only has to be balanced
3. You CANNOT split compounds to write in a
coefficient:
HCl
Rules to Balancing Chemical Equations
4. Only multiply through when it is a compound
because they have already bonded
2H + Cl
NO
2HCl
YES
5. If it is a capital letter, they are each a
separate element:
H, C, O
If it is a capital letter followed by a lower
case letter, it is all one element:
Cl, Li, Si
Steps for Balancing Chemical Equations


1. Divide the reactants from the products
with a line.
2. Write down the chemical symbol of each of
the elements on each side of the equation
2 H2 + O
2
2H2O
H=
H=
O=
O=
Steps to Balancing Chemical Equations


3. Using the coefficients and subscripts write
down the number of each element
4. If they are not balanced change the
coefficients using trial and error. You will have
to go back and forth between each side!
2 H2 + O
2
2H2O
H=4
H=4
O=2
O=2
Back to Page 28:
Lets Do a Few Together…
Cl2 + KI
KCl + I2
Lets Do a Few Together…
CH4 + O2
CO2 + H2O
Lets Do a Few Together…
Li + H2O
LiOH + H2
Complete
the
Practice
Worksheet
Extra Credit: Sum It Up!
Copy these 3 questions, and then answer them in
complete sentences for 5 points extra credit!
1. What does the Law of Conservation of Mass
(Matter) state, and what does that really
mean?
2. Explain how either the dry ice demo or the
balloon experiment from last class demonstrated
the Law of Conservation of Mass (Matter)?
3. How is the Law of Conservation of Mass
(Matter) the key to balancing chemical
equations?