Download PART 2 - Changes in the Properties of Matter: Physical and Chemical

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HOMEWORK PACKET – CHANGES & BALANCING
Chapter 21 Review Questions
PART 1 - Use your book to answer the following questions
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Are atoms made of molecules, or are molecules made of atoms?
Which is smaller: the microscopic or the submicroscopic?
What is a physical property?
What is a chemical property?
What doesn't change during a physical change?
Why is it sometimes difficult to decide whether an observed change is physical or chemical?
What are some of the clues that help us determine whether an observed change is physical or chemical?
Is it possible for an element to have more than one atomic formula?
How many atoms are in a sulfur molecule that has the elemental formula S 8?
What is the difference between an element and a compound?
11.
How many atoms are there in one molecule of H3PO4? How many atoms of each element are there in one
molecule of H3PO4?
12.
Are the physical and chemical properties of a compound necessarily similar to those of the elements from
which it is composed?
13.
14.
15.
What is the purpose of coefficients in a chemical equation?
What do the letters (s), (l), (g), and (aq) stand for in a chemical equation?
Why is it important that a chemical equation be balanced?
1
16.
17.
18.
Why is it important never to change a subscript in a chemical formula when balancing a chemical equation?
Which equations are balanced?
Classify the following changes as physical or chemical. Even if you are incorrect in your assessment, you should
be able to defend why you chose as you did.
a. grape juice turns to wine
b. wood burns to ashes
c. water begins to boil
d. a broken leg mends itself
e. grass grows
f. an infant gains 10 pounds
g. a rock is crushed to powder
19.
Is the following transformation representative of a physical change or a chemical change?
20.
Each sphere in the diagrams below represents an atom. Joined spheres represent molecules. Explain what’s
happening in the picture.
21.
22.
23.
What physical and chemical changes occur when a wax candle burns?
Which elements are some of the oldest known? What is your evidence?
Oxygen atoms are used to make water molecules. Does this mean that oxygen, O 2, and water, H2O, have
similar properties? Why do we drown when we breathe in water despite all the oxygen atoms present in this
material?
PART 2 - Changes in the Properties of Matter: Physical and Chemical
2
What is MATTER?
What’s SOLUBILITY?
What’s a PROPERTY?
Compare and contrast mixtures and solutions.
What’s the relationship between elements and
atoms?
What’s a CHEMICAL CHANGE?
List and describe all the PHYSICAL PROPERTIES that
are mentioned.
What happens in a chemical reaction?
What’s the difference between malleability and
brittleness?
How do you know if a chemical change has
occurred? SIGNS
What’s a CHEMICAL PROPERTY?
Give some examples of chemical changes.
Name some chemical property tests.
What’s a PHYSICAL CHANGE?
When is it hard to tell if something is a mixture?
What’s a physical separation?
What happens when the rocket takes off in terms of
a chemical change?
What happens when you run electricity through
water?
How is digestion a chemical change?
Give some examples of confusing physical/chemical
changes.
What’s a solution? Name some.
Explain what happens when something DISSOLVES.
3
PART 3 - Identify each of the following as a Physical or Chemical Change.
Put a P next to Physical Changes Put a C next to Chemical Changes
1. A piece of wood burns to form ash. _________
2. Water evaporates into steam. _________
3. A piece of cork is cut in half. _________
4. A bicycle chain rusts. _________
5. Food is digested in the stomach. _________
6. Water is absorbed by a paper towel. _________
7. Hydrochloric Acid reacts with zinc. _________
8. A piece of an apple rots on the ground._________
9. A tire is inflated with air. _________
10. A plant turns sunlight, CO2, and water into sugar and oxygen. _________
11. Sugar dissolves in water. _________
12. Eggs turn into an omelet. _________
13. Milk sours. _________
14. A popsicle melts. _________
15. Turning brownie mix into brownies. _________
Choose 2 of the above examples and explain why you chose chemical or physical. Please choose one of each
type of change. Back up your explanation.
Physical change explanation:
_______________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
Chemical change explanation: _______________________________________________
_______________________________________________________________________
_______________________________________________________________________
_______________________________________________________________________
PART 4 – DEALING WITH CHEMICAL EQUATIONS
Fill in the blank with the appropriate term(s).
chemical change
coefficient
balanced equation
chemical reaction
subscript
physical property
physical change
1. The “3” in CaCO3 ________________________________________
2. The state, size, or shape of a substance ________________________________________
3. The “6” in 6H2O________________________________________
4. What happens when two substances react to produce entirely different
substances________________________________________
4
5. An equation with an equal number of atoms in the reactants and
products________________________________________
6. Ice melting is an example of this kind of change ________________________________________
7. You cannot create or lose mass in a ________________________________________
PART 5 - Counting Atoms
The formula for a compound indicates the elements that make up the compound and the
number of atoms of each element present in the compound. These numbers of atoms are
indicated by the use of small numbers called subscripts. Sometimes groups of atoms act as a single
atom. Such a group of atoms is called a polyatomic ion. If a polyatomic ion is used in a formula
more than once, it is put in parentheses and the subscript appears outside of the parentheses. When
a
subscript appears outside the parentheses, it indicates that all of the elements inside the parentheses
should
be multiplied by that subscript. For example, the formula Fe(OH) 3 indicates the combination of one atom of iron, Fe,
three atoms of oxygen, O, and three atoms of hydrogen, H.
In the following examples, list each element in the compound and the number of atoms of each element present.
The first example has been done for you. You may already be familiar with some of the compounds.
Name
Use
Formula
Calcium carbonate
Limestone
CaCO3
Aspirin
Pain reliever
C9H8O4
Magnesium hydroxide
Found in milk of magnesia
Paradichlorobenzene
Moth crystals
C6H4Cl2
Acetic acid
Found in vinegar
C2H4O2
Trinitrotoluene (TNT)
Explosive
Calcium dihydrogen
phosphate
Fertilizer
Pyrite
Fool’s gold
Sucrose
Sugar
Atoms in Formula
Ca = calcium =1
C = carbon = 1
O = oxygen =3
Mg(OH)2
C7H5(NO2)3
Ca(H2PO4)2
FeS2
C12H22O11
5
Name
Use
Formula
Sulfuric acid
Used in car batteries
Cellulose
Found in wood products such
as your pencil and paper
Asbestos
Insulator
Dichlorodiphenyltrichloroethane
(DDT)
Banned pesticide
Silicon dioxide
Sand
SiO2
Iron oxide
Rust
Fe2O3
Butane
Lighter fluid
C4H10
Atoms in Formula
H2SO4
C6H7O2(OH)3
H4Mg3Si2O9
C14H9Cl5
PART 6 – BALANCING EQUATIONS
(1) Circle each subscript in each chemical formula.
(2) Draw a square around each coefficient.
(3) Answer the questions related to each chemical formula.
How many atoms of Hydrogen are in this
formula as shown?
2
______
What element does the O represent?
___________________
1.
O
2. CO2
How many atoms of each element are in the
formula shown?
C = ______ O = ______
3. 5H2
4. 2C2H6
How many atoms each element are in the
formula shown?
C = ______ H = ______
5. 2Na2SO4
How many atoms each element are in the
formula shown?
Na = ______ S = ______ O = ______
6
6. H2
What element does the H represent?
___________________
7. SO4
How many atoms of each element are in the
formula shown?
S = ______ O = ______
8. 5C2
How many atoms of carbon are in this formula
as shown?
______
9. 2Fe(OH)3
How many atoms each element are in the
formula shown?
Fe = ______ O = ______ H= ______
10. Al(OH)2
How many atoms of each element are in the
formula shown?
Al = ______ O = ______ H = ______
7
Part B: Label the chemical equation using PRODUCT, REACTANT, SUBSCRIPT, COEFFICIENT, and
YIELDS.
2 Mg + O2
2 MgO

Part C: Balance each of the following equations. Remember to count your atoms!
1.
H2
2.
H2O2
3.
Na
+
O2

H2O

H2O
+
O2
+
O2

Na2O
4.
N2
+
H2

NH3
5.
P4
+
O2

P4O6
6.
C
+
H2

CH4
7.
Al2 O3

Al +
O2
8.
Fe
+ H2O 
9. C2 H6
10. Na2SO4
+
Fe3O4
O2 
+
CaCl2
+
CO2

+
CaSO4
NO
MORE!
H2
H2O
+
NaCl
8
Atoms are not _______________ or _____________ during a chemical reaction. We know this because
of the Law of ____________________________. Scientists know that there must be the ___________
number of atoms on each ___________ of the ____________. To balance the chemical equation, you
must add _______________ in front of the chemical formulas in the equation. You cannot _______ or
___________ subscripts!
Part A: Identify the following parts of each chemical formula by circling the subscripts and drawing a
square around the coefficients.
H2
2 HCl
4 O2
CH4
3 CO3
2 NaOH
Part B: List the symbols for the atoms in each formula and give the number of each.
C2H6
NH3
2MgO
3 Al(OH)3
4P4O10
2 H2O2
Steps:
1) Determine number of atoms for each element.
2) Pick an element that is not equal on both sides of the equation.
3) Add a coefficient in front of the formula with that element and adjust your counts.
4) Continue adding coefficients to get the same number of atoms of each element on each side.
For Example:
Mg +
O2
Mg =

MgO
O=
Mg =
Try these:
1. Ca
+
O2

2. N2
+
H2

Ca =
N=
3. Cu2O
Cu =
4. H2O2
H=
O=
H=
Ca =
N=
+
C


H2O
+
O=
O=
O=
C=
H=
CaO
NH3
Cu
Cu =
O=
H=
+
CO2
O=
C=
O2
O=
More Balancing Act Practice
Continue to balance each equation. Remember you cannot add subscripts or place coefficients in the
middle of a chemical formula!!!!
1.
Na
+
MgF2 
NaF
+
Mg
9
2.
Mg
+
HCl

MgCl2 +
H2
3.
Cl2
+
KI

KCl
+
I2
4.
NaCl

Na
+
Cl2
5.
Na
+
O2

Na2O
6.
Na
+
HCl

H2
+
NaCl
7.
K
+
Cl2

KCl
Challenge: This one is tough!
C2H6 +
O2

CO2
+
H2O
10