Chapter 7.1 Notes
Describing Reaction
Physical VS Chemical Properties
a. Physical vs Chemical Properties
a. Physical Change – A change that
occurs when some of the
properties of a material change, but
the substances in the material
remain the same.
b. Chemical Change – A change that
occurs when a substance reacts and
forms on or more new substances.
Physical VS Chemical Properties
i. Signs of a chemical change include
color change, temperature change,
light produced, gas formed,
precipitate formed.
c. When matter undergoes a chemical
change, the composition of the matter
changes. When matter undergoes a
physical change, the composition of the
matter remains the same.
Chemical Reactions
a. Chemical Reactions
a. A useful description of a chemical
reaction tells you the substances
present before and after the
reaction.
b. Reactants – The substances that
undergo change and are present
before the reaction takes place.
Chemical Reactions
c. Products – The new substances formed
as a result of that change and are
present after the reaction takes place.
d. A chemical equation is a representation
of a chemical reaction in which the
reactants and products are expressed as
formulas.
e. Reactants  Products
Example 1: Burning Charcoal
• Word Equation:
Carbon + Oxygen = Carbon Dioxide
•
Chemical Formula:
C + O2 = CO2
Conservation of Mass
c. Conservation of Mass
a. The Law of Conservation of Mass
states that mass is neither created
nor destroyed in a chemical
reaction.
b. Therefore the mass of the products
is always equal to the mass of the
reactants.
Conservation of Mass
c. While burning charcoal you actually see the
charcoal burn and disappear. The same mass of
charcoal that appears to have disappeared is
actually converted into carbon dioxide gas.
Balancing Equations
d. Balancing Equations
a. In order to show that mass is conserved
during a reaction, a chemical equation
must be balanced.
b. Chemical equations can be balanced by
changing the coefficients (the numbers
that appear before symbols.)
c. When balancing a chemical equations
never change the subscripts in the
formula.
E. Steps to Balancing a Chemical Formula
e. Steps to Balancing a Chemical Formula
a. Step 1: Count the number of atoms of
each element on each side of the
equation.
b. Step 2: change one or more coefficients
until the equation is balanced. (Only
change the coefficients that need to be
changed.)
Ex. 1) Write a balanced equation for the reaction between
copper and oxygen to produce copper(II) and oxide, CuO.
What do you Know?
- Reactants: Cu, O2
- Product: CuO
What do you need to know?
- Balanced Equation
Plan and Solve:
- Write a chemical equation with the
reactants on the left side and the
product on the right side
- Cu + O2  CuO
- Change the coefficient of CuO in
order to balance the number of O
atoms.
- Cu + O2  2CuO
- Change the coefficient of Cu.
- 2Cu + O2  2CuO
Answer:
Ex. 2) Balance the equation H2O2  H2O + O2
What do you Know?
- Reactants: H2O2
- Product: H2O + O2
What do you need to know?
- Balanced Equation
Plan and Solve:
- Write a chemical equation with the
reactants on the left side and the
product on the right side
- H2O2  H2O + O2
- Change the coefficient of H2O2 and
H2O in order to balance the number
of H and O atoms.
- 2H2O2  2H2O + O2
Answer:
Ex. 3) Balance the equation Mg + HCl  H2 + MgCl2
What do you Know?
- Reactants: Mg, HCl
- Product: H2, MgCl2
What do you need to know?
- Balanced Equation
Plan and Solve:
- Write a chemical equation with the
reactants on the left side and the
product on the right side
- Mg + HCl  H2 + MgCl2
- Change the coefficient of HCl in
order to balance the number of H
and Cl atoms.
- Mg + 2HCl  H2 + MgCl2
Answer:
Counting With Moles
f. Counting With Moles
a. A mole is an amount of a substance that
contains approximately 6.02 X 1023
particles of that substance. This number
is known as Avogadro’s number
b. Because chemical reactions often
involve large numbers of small particles,
chemists use a counting unit called the
mole to measure amounts of a
substance.
Molar Mass
g. Molar Mass
a. Molar mass is the mass of one mole of a
substance.
b. In the same way that a dozen eggs has a
different mass than a dozen oranges, a
mole of carbon would have a different
mass than a mole of sulfur.
c. The molar mass is the same as the
atomic mass expressed in grams
Molar Mass
d. For a compound you can calculate the molar
mass by adding up the atomic masses of its
component atoms, and then expressing the sum
in grams.
Ex. 4) Find the molar mass of a molecule of CO2.
• One carbon= 12amu
• Two Oxygen= 16amu x 2 = 32amu
• 12amu+32amu = 44.0 grams.
Mole-Mass Conversion
h. Mole – Mass Conversion
a. Once you know the molar mass of a
substance, you can convert moles of
that substance into mass, or a mass
of that substance into moles.
Ex. 5) Convert 55.0 g of CO2 to moles.
What do you know?
44.0 g CO2 = 1 mol CO2
What do you want to know?
55.0g CO2 in moles
Plan and Solve:
Use a conversion factor.
55.0g CO2 X (1mol CO2/44.0g CO2)
Answer:
• = 1.25mol CO2
Ex. 6 Convert 144g of H2O to moles
What do you know?
What do you want to know?
• 18g of H2O = 1 mol of H2O • How many moles is 144g of
H2O?
Plan and Solve:
• Use a conversion factor.
• 144g H2O X (1mol H2O/18g H2O)
Answer:
• 144g H2O = 8.00 mol H2O