Unit 4 Lesson 1 Chemical Reactions
Essential Question: How are Chemical
Reactions Modeled?
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Chemical Reactions
Chemical Reactions
Essential Question:
How are chemical reactions
modeled?
Key Topics
Chemical reactions
Chemical equations
Energy
Reaction rates
Chemical Reactions
p214
What are the signs of a chemical reaction?
Properties and Changes in Matter
• A chemical reaction is the process in which atoms are
rearranged to produce new substances.
• During a chemical reaction, the bonds that hold atoms together
may be formed or broken.
• The properties of the substances produced in a chemical
reaction differ from the properties of the original
substances.
Chemical Reactions
p214
What are the signs of a chemical reaction?
Evidence for Chemical Reactions
Chemical reactions involve two main kinds of changes that
you can observe:
Formation of new substances and Changes in Energy.
Color Change
Precipitate may form (a solid substance from 2 liquids)
Production of gas (bubbles)
Change in Odor
Change in Energy: absorb or release energy
Endothermic
Exothermic
Chemical Reactions
P218-219
What happens to energy during a chemical
reaction?
Exothermic vs. Endothermic
Exothermic (Heat Out)
Releases Energy – usually
in the form of heat, light,
and/or sound
Endothermic (Heat In)
Requires an input of energy
Energy is constantly added for a
chemical reaction to occur
Energy is absorbed from the
surroundings, usually as
heat - which makes it get
colder.
Total amount of energy does not change
Energy cannot be created or destroyed
Chemical Reactions
p215
How are Chemical Reactions Modeled?
Describing Chemical Reactions
Cellular phone messages make use of symbols and
abbreviations to express ideas in shorter form.
Similarly, chemists often use chemical equations in place of
words.
Chemical Reactions
p215
How are Chemical Reactions Modeled?
Chemical Formulas
•A chemical formula uses
chemical symbols and
numbers to represent a
given substance.
•The chemical symbols in a
chemical formula tell you
what elements make up a
substance.
•The numbers written
below and to the right of
chemical symbols are called
subscripts. Subscripts tell
you how many of each type of
atom are in a molecule.
Chemical Reactions
How are Chemical Reactions Modeled?
p215
Chemical equations use chemical formulas and other symbols
instead of words to summarize a reaction.
Chemical Reactions
p216
How do Chemical equations show the law
of conservation of mass?
Conservation of Mass
The principle of conservation of mass states that in a chemical
reaction, the total mass of the reactants must equal the total mass
of the products.
Matter cannot be created nor destroyed, only changes
forms
Chemical Reactions
p216
How do Chemical equations show the law
of conservation of mass?
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must
show the same number of each type of atom on both sides of
the equation.
Chemical Reactions
p216
How do Chemical equations show the law
of conservation of mass?
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must
show the same number of each type of atom on both sides of
the equation.
Chemical Reactions
p216
How do Chemical equations show the law
of conservation of mass?
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must
show the same number of each type of atom on both sides of
the equation.
Chemical Reactions
p216
How do Chemical equations show the law
of conservation of mass?
Balancing Chemical Equations
To describe a reaction accurately, a chemical equation must
show the same number of each type of atom on both sides of
the equation.
Chemical Reactions
How do Chemical equations show the law
of conservation of mass?
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of
sodium metal (Na) with oxygen gas (O2),
forming sodium oxide (Na2O).
Chemical Reactions
How do Chemical equations show the law
of conservation of mass?
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of
sodium metal (Na) with oxygen gas (O2),
forming sodium oxide (Na2O).
Chemical Reactions
How do Chemical equations show the law
of conservation of mass?
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of tin
(Sn) with chlorine gas (Cl2), forming tin
chloride (SnCl2).
Chemical Reactions
How do Chemical equations show the law
of conservation of mass?
Balancing Chemical Equations
Balancing Chemical Equations:
Balance the equation for the reaction of tin
(Sn) with chlorine gas (Cl2), forming tin
chloride (SnCl2).
Chemical Reactions
Balancing Act
Evidence:
Fizzing, Bubbling
Production of a gas
Change in smell
Change in texture
This reaction is Exothermic.
If you felt on the bottom of the watch glass
you would have felt the glass get warmer
Evidence:
Color Change
white yellow  brown  black
Change in Smell
Production of a gas – bubbling
Change in Energy
This reaction is Endothermic.
You had to keep it over the flame to keep
the reaction from stopping.
Evidence:
Color change of solution (blue to gray
and Aluminum foil (shiny metal to red/brown
clay-like material
Change in energy
small amount of bubbling
This reaction is Exothermic.
The temperature rose about 10 degree
Celsius. The glass felt warm to touch
Chemical Reactions
p220
The Need for Speed
What affects the rates of reactions?
• The rate of a reaction describes how quickly the
reaction occurs.
• For a reaction to occur, particles of the reactants must
collide. Reaction rates are affected by how often the
particles collide.
• Factors that affect reaction rates include:
concentration
surface area
Temperature
presence of a catalyst.
Chemical Reactions
What affects the rates of reactions? p220
• At higher concentrations, there are more reactants in a given
volume, so the particles are more likely to collide and react.
• The reaction rate is higher when reactant concentration is
higher.
• Crushing or grinding solids increases their surface area and
the reaction rate, as more reactant particles are exposed to
one another.
• Reactions usually occur more quickly at higher temperatures.
The reactant particles move more quickly, so they are more
likely to collide and react.
• A catalyst is a substance that changes the rate of a chemical
reaction without being used up or changed very much.
Chemical Reactions
p220
Chemical Reactions
p220
Chemical Reactions
p220
Chemical Reactions
p220
Chemical Reactions
p220
Chemical Reactions
p220
Chemical Reactions
Chemical Reactions
Relating Cause and Effect
Causes
Effect
Increased rate of reaction
Chemical Reactions
Relating Cause and Effect
Causes
Increase in surface area
Effect
Increase in temperature
Increased rate of reaction
Increase in concentration
of reactants
Use of a catalyst
Chemical Reactions
Graphic Organizer
Chemical
reactions
can be
are written as
balanced with
which require
Activation
energy
written using
Chemical Reactions
Graphic Organizer
Chemical
reactions
can be
Endothermic
reactions
are written as
Exothermic
reactions
Equations
balanced with
which require
Activation
energy
written using
Chemical
symbols
Coefficients
Arrows and
plus signs
Atoms, Periodic Table,
Bonding – TEST answers
1) C
2) D
3) C
4) A
5) D
6) A
7) B
8) A
9) B
10)C
11) C
12) A
13) A
14) A
15) B
16) C
17) D
18) D
19) D
20) B
21) C
22) A
23) B
24) A
25) B
26) B
27) D
28) D
29) B
30) A
31) C
32) C
33) C
34) A
35) C