Download Chapter 7

Burning is an example of a
chemical reaction. When charcoal
burns, the carbon in the charcoal
reacts with oxygen in the air to
produce carbon dioxide and heat.
Girl mixing chemicals: https://youtu.be/AhG1nv1T6ZA
Mr Bean: https://www.youtube.com/watch?v=6aK2CKrdjbE
Chemical Reaction compilation:
https://www.youtube.com/watch?v=8TPnns-5UxA
CHAPTER 7
Chemical Reactions
7.1 DESCRIBING REACTIONS
What are Chemical Equations?
• A chemical reaction tells you the
substances present before and after a
reaction
• Reactants-substances that undergo
change
• Products-The new substances formed as a
result of that change
USING EQUATIONS TO
REPRESENT REACTIONS
• Reactants change into products
• Reactants  Products
• Carbon + Oxygen  Carbon Dioxide
•C
+
O2

CO2
• Chemical Equation is a representation of a chemical
reaction in which the reactants and products are
expressed as formulas.
• “Carbon and oxygen react and form carbon dioxide”
PRACTICE YOURSELF
Label the reactants and products for each:
1. Blue + Yellow  Green
Reactants:
Products:
2. Gasoline + Fire  Heat + Smoke
Reactants:
Products:
3. Gatorade  K+ ions + Na+ ions + Sugar
Reactants:
Products:
CONSERVATION OF MASS
• Mass of the products is always ___________ to the
mass of the reactants.
• French chemist Antoine Lavoisier (1743–1794),
developed the law of conservation of mass.
• The law of conservation of mass states that mass is
neither created nor destroyed in a chemical reaction
Atoms are not
created OR
destroyed
during a
reaction
Whether you burn one carbon atom or six
carbon atoms, the equation used to describe
the reaction is the same.
CONSERVATION OF MASS
6
12
18
PARTS OF AN EQUATION
2C + 2S2  2CS2
Definitions:
• Subscript:
• Coefficient:
• Yield sign:
• Reactants:
• Products:
MOLAR MASS (ABBREV MM)
What is a Mole?
• Basically, a mole is a unit of something
• Molar Mass is the mass of the parts of a molecule
• The same mass that’s on the periodic table
Ex1: Molar Mass of Sodium (Na) is 23
Ex2: Molar Mass of Chlorine is 35.45
Ex3: MM of salt (NaCl) MUST be broken down into Na and Cl
- The MM of Na is 23
- The MM of Cl is 35.45
- The combined mass of NaCl is 58.45
Add
23 + 35.45
Now… use Molar Mass to balance
an Equation
1.
2C +
2S2 
2CS2
PO4
2.
2 O2 +
P 
3.
NH4 +
KCl

KH3 +
HCl
MOLAR MASS… CONTINUED
CO2
NaNH4
Ba3(PO4)2
BALANCING EQUATIONS
• In order to show mass is conserved,
the chemical equation must be
balanced.
•
N2H4 +
N
H
O
2
4
2
O2 
N2 + _ 2_ H2O
N 2
H 2 x_2_ =4
O 1 x _2_=2
CHEMICAL EQUATIONS
Steps for solving Chemical Equations
Step 1: Assume the equation is WRONG
Step 2: Write the # of atoms for each “side” of the
equation
Step 3: Make adjustments to the “sides” to make sure
that the masses balance out
Ca
Ca=
Cl=
+
Cl 
CaCl2
Ca=
Cl=
NOW SLIGHTLY HARDER…
I2 + NaCl 
I=
Na =
Cl =
NaI +
I=
Na =
Cl =
Cl2
To balance a
chemical
equation, first
count the
atoms on
each side of
the equation.
BALANCING RULES
• Coefficients- the numbers that appear
before the formulas.
• In the unbalanced equation above, the
coefficients are understood to be 1__
• When you change a coefficient, you
change the amount of that reactant or
product represented in the chemical
equation.
• As you balance equations, you should
never change the subscripts in a formula
PRACTICE
1. Hydrogen chloride, or HCl, is an important industrial
chemical. Write a balanced equation for the production of
hydrogen chloride from hydrogen and chlorine.
2. Balance the following chemical equations.
3. Ethylene, C2H4, burns in the presence of oxygen to produce
carbon dioxide and water vapor. Write a balanced equation
for this reaction
7.2 TYPES OF REACTIONS
Just as you can classify matter into different types, you
can classify chemical reactions into different types
Some general types of chemical reactions are:
1.
2.
3.
4.
5.
Synthesis reactions
Decomposition reactions
Single-replacement reactions
Double-replacement reactions
Combustion reactions
1. SYNTHESIS
(COMBINATION)
• A + B  AB
• Ex: 2Na + Cl2 2 NaCl
2H2 + O2  2H2O
• Two or more substances
react to form a single
substance.
Sodium metal reacts vigorously
with chlorine to form sodium
chloride, NaCl
2. DECOMPOSITION
• AB  A + B
• Ex: 2H2O  2H2 + O2
CaCO3  CaO + CO2
• A compound breaks down into two or
more simpler substances.
3. SINGLE REPLACEMENT
• AB + C  A + BC
• Ex: Cu + 2Ag(NO3)  2Ag + Cu(NO3)
K + 2H2O  H2 + 2KOH
• One element takes the place of another element in a compound
A single-replacement reaction occurs when
copper wire is submerged in a solution of silver
nitrate.
Potassium reacts with water in a
single-replacement reaction
that produces hydrogen gas
and potassium hydroxide.
4. DOUBLE REPLACEMENT
• AB + CD  AD + CB
• Ex: Pb(NO3) 2 + 2KI  PbI2 + 2KNO3
CaCO3 + 2HCl  CaCl2 + H2CO3
• Two different compounds exchange
positive ions and form two new
compounds.
When potassium iodide solution is poured into a solution
of lead(II) nitrate, a double-replacement reaction takes
place. Lead(II) iodide forms as a yellow precipitate.
5. COMBUSTION
• Ex: CH4 + 2O2  CO2 + 2 H2O
A substance reacts rapidly with oxygen, often
producing heat and light.
• Ex: 2H2 + O2  2H2O
Notice that you could also classify this reaction
as the synthesis of water. The classifications for
chemical reactions sometimes overlap
Practice on worksheet 8 ……
Continue by finishing Page 6 and 7
A Bunsen burner generates
heat and light by the
combustion of natural gas.
SUMMARY OF REACTION TYPES
7.4 REACTION
RATES
Reaction Rates- Rate at which reactants change into
products over time.
• Reaction rates tell you how fast a reaction is going.
• That is, how fast the reactants are being consumed,
how fast the products are being formed, or how fast
energy is being absorbed or released
NEXT TOPIC…
Factors that affect the SPEED of reactions
FACTORS AFFECTING
REACTION RATES
1. Temperature - Generally, an increase in
temperature will increase the reaction rate.
• Ex: You store milk in a refrigerator to slow down the
reactions that cause the milk to spoil
• Increasing the temperature of a substance causes its
particles to move faster, on average.
• Particles that move faster are both more likely to
collide and more likely to react.
• If the number of collisions that produce reactions
increases, then the reaction rate increases
FACTORS AFFECTING
REACTION RATES
2. Surface Area - An increase in surface area increases
the exposure of reactants to one another.
• The smaller the particle size of a given mass, the
larger is its surface area.
• An increase in surface area increases the exposure
of reactants to one another.
• The greater this exposure, the more collisions there are
that involve reacting particles.
• With more collisions, more particles will react. This is why
increasing the surface area of a reactant tends to
increase the reaction rate.
FACTORS AFFECTING REACTION RATES
3. Stirring - Stirring the reactants will generally increase
the reaction rate. Collisions between the particles of the
reactants are more likely to happen
• Ex: A washing machine speeds up the reaction by
stirring the contents back and forth
FACTORS AFFECTING
REACTION RATES
4. Concentration - The more reacting particles
present, the more opportunities there are for collisions
involving particles.
• For gases, concentration changes with pressure. The
greater the pressure of a gaseous reactant, the
greater is its concentration, and the faster is the
reaction rate.
The dye solution in the left beaker
is more concentrated than the
solution in the right. Increasing the
concentration of the dye
increases the rate of color
change in the material.
FACTORS AFFECTING
REACTION RATES
5. Catalysts - A substance that affects the reaction
rate without being used up in the reaction.
• Catalysts are used so reactions can occur at lower
temperatures.
Catalysts are written above the arrow.
• Energy is needed to start breaking the chemical
bonds. This is called activation energy. Catalysts
lower that energy needed by providing a surface on
which the reacting particles can come together.
HOW A CATALYST WORKS
The graph
shows how a
catalyst lowers
the amount of
energy required
for effective
collisions
between
reacting
particles.
MOLAR MASS QUIZ
Directions: Show all work, include unit of
measurement, and circle final answer.
H2O
(NH3)4
C2H4O2
K2Cr2O7
DO NOW
1.
What is the molar mass of:
a) C6H12O6 (a sugar molecule)
b) O3 (An Ozone molecule)
2. Using the terms in the equation below,
explain how carbon is the same on
each
side of the equation… as the
Law of
Conservation of Mass says.
Wood + O2 + spark = ashes + CO2
DO NOW
Balance the following reactions:
1. ___ Fe2O3 + ___C  ___Fe + ___CO2
2. _____NO + ____O2  _____NO2
3. ____CO2 + ____H2  ___CO + ___H2O