Transcript chemical reaction

Chapter 14
Chemical Reactions
Little book chapter 2 (page 26-54)
Section 1 Objectives
• Describe how chemical reactions produce new substances
that have different chemical and physical properties.
• Identify four signs that indicate that a chemical reaction might
be taking place.
• Explain what happens to chemical bonds during a chemical
reaction.
Chemical Reactions
• A _________________ is a process
in which one or more substances
change to make one or more ____
substances.
• The chemical and physical
properties of the substance will
__________.
Chemical Reactions
Signs of a chemical reaction:
- ___________ – solid substance that is
formed in a solution.
- ___________
- Heat __________
- Electricity
- _______ change
- ___________ formation
Signs of chemical reactions
5
The dark red precipitate is
called silver chromate. It is
formed when potassium
chromate is added to a silver
nitrate solution.
Nitrogen dioxide gas is formed when
copper is placed into nitric acid.
Energy is released during some
chemical reactions.
Bleach reacts with the dye on the
fabric and causes the color of the
material to change.
Section 2 Objectives
• Interpret and write simple chemical formulas.
• Write and balance simple chemical equations.
• Explain how a balanced equation shows the law of
conservation of mass.
Chemical Formulas
• The names of many ________ compounds use
prefixes to express the number of ______ of each
element.
mono-
____ Hexa-
6
di-
2
hepta-
7
_____
3
______
8
tetra-
4
nona-
9
_____
5
deca-
_____
Chemical Formulas 2
• In an ______ compound the name of metallic
element is written first and _____ is added to
the nonmetal.
Chemical Equations
• A chemical equation is a representation of a
chemical reaction in which the reactants and
products are expressed as formulas.
• Reactant + Reactant → Product
• __________ are the substances that undergo
the change.
• Products are the new ________ formed.
C + O2 → CO2
Reactants → _________
2+3=5
• Antoine Lavoiser determined that the mass of the
products is always _______ to the mass of the
reactants.
• The ______________________ states that mass
is neither created nor destroyed in a chemical
reaction.
• In order to show mass is
conserved an chemical
equation must be __________.
Balanced Equations
• Equations need to be balanced.
• Matter can not be created nor
___________. This means there needs
to be the same number of ______ on
each side of the equation.
• The equation below is balanced
• S8 + 12 O2→8 SO3
Balanced Equations
• Subscript
• small numbers to the lower right of
chemical symbols
• represent the number of _______ of
each element in the molecule
• Coefficients
• large numbers in front of chemical
formulas
• represent the number of ___________ of
the substance in the reaction
How Many Atoms?
• Using coefficients and subscripts to count
atoms in equations:
• number of atoms = coefficient X
subscript
• Example: How many of each type of atom
are represented by: 2Al2(SO4)3
• # of Al atoms = 2 X 2 = 4
• # of S atoms = 2 X 1 X 3 = 6
• # of O atoms = 2 X 4 X 3 = 24
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Section 3 Objectives
• Describe four types of chemical reactions.
• Classify a chemical equation as one of four types of chemical
reactions.
Types of Reactions
• A ___________ reaction is a
reaction in which ____ or more
substances form a single substance.
(Simple → Complex)
• A + B → AB
• A ___________ reaction is when a
compound breaks down into _____ or
more simpler substances. (Complex
→ Simple)
• AB → A + B
Types of Reactions
• Single _____________ reaction in which
one element takes the place of another
element in a compound.
• (One person breaks up a couple and goes
out with one of them.
• A + BC→ AC + B
Types of Reactions
• Double ___________ reaction is one
in which _____ different compounds
exchange ________ ions and form
two new compounds.
• AB + CD → AD + CB
Energy Changes
• Chemical energy
• the energy _______ in the chemical
bonds of a substance.
• Breaking a chemical bond requires
_________.
• During a chemical reaction, energy is
either
• ______________
• ______________
Section 4 Objectives
• Compare exothermic and endothermic reactions.
• Explain activation energy.
• Interpret an energy diagram.
• Describe five factors that affect the rate of a reaction.
Conservation of Energy Review
• The law of conservation of
energy states
• neither mass or energy can be
_______ or _________ in a
chemical reaction.
• Energy can be
• __________ from one object to
another.
IN/OUT
• _____________ Reaction
• the energy released as the products form is
_________ than the energy required to break
the bonds.
• Reaction in which energy is
• ______________
• Exo = ___________
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Examples:
Fire
Digestion
Hand warmers
IN/OUT
• _____________ Reaction
• ________ energy is required to ________ the bonds in
the reactants than is released by the formation of the
products.
• Reaction in which energy is taken in
• Endo = ____________
• Examples:
• Alka-seltzer
• Ice packets
• Camera
Reaction Rate
•Reaction rates
•tell you how _______ a reaction
is going.
Factors That Affect Reaction
Rates
• Temperature
• – Increasing temperature _________
the reaction rate.
• Stirring
• – increases the exposure of the
reactant _________ the reaction rate.
Factors That Affect Reaction
Rates
• Surface Area
• Increasing surface area _________
the reaction rate
• The larger the surface area, the ____
the reaction rate
• Concentration
• increasing concentration ________
the reaction rate.
Factors That Affect Reaction
Rates
•Catalyst
• a substance that _________ the
reaction rate ________ being used
up in the reaction.
• A substance that ______ up a
reaction without being permanently
changed. NOT A ___________!!
• Ex: __________ speed up reactions
in your body.
Get Started
• Many reactions
• occur at room temperature, but some
need a “little help” to get started.
• You may need to add
• _________ (Lighting a candle) or
• __________ (Diesel engine)
• Start a reaction
Activation Energy
• ______________ ENERGY
• Energy needed to _________ a reaction.
• This is represented by an activation
curve on a graph.
Reaction Rate & Catalyst
• You can speed up a
reaction (rxn) rate by:
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Increasing ____________
Increase Surface Area
Increase Concentration
Using a ____________
• A catalyst is a substance
that speeds up a reaction
without being part of the
reaction.
• A catalyst works by
• _________ the
amount of _________
energy required for
the reaction to occur.
• Remember, reactions
require
• _________________
• catalyst simply lowers
the amount of energy.
Catalyst Continued
• A catalyst is neither
• a reactant or
• a _____________
• When you finish the
reaction __ the catalyst
is still there – none was
used or changed in the
reaction.
Inhibit
• An _______ is a
substance that _____
down or stopping a
reaction may
sometimes be useful.
• Examples:
• Penicillin
• Preservatives
• Fungicide
Section 1 Review
• 1. Use the following terms in the same sentence: chemical
reaction and precipitate.
• 2. Most chemical reactions:
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A. have starting substances that collide with each other.
B. do not break bonds.
C. do not rearrange atoms.
D. cannot be seen.
• 3. If the chemical properties of a substance have not changed,
has a chemical reaction occurred?
• 4. Steam is escaping from a teapot. Is this a chemical reaction?
Explain.
Section 2 Review
• 1. Make the following statement TRUE: A chemical formula
describes a chemical reaction
• 2. Make the following statement TRUE: The substances
formed from a chemical reaction are reactants.
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A. have starting substances that collide with each other.
B. do not break bonds.
C. do not rearrange atoms.
D. cannot be seen.
• 3. The correct chemical formula for carbon tetrachloride is:
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A. CCl3
B. C3Cl
C. CCl
D. CCl4
Section 3 Review
• 1. In your own words, write a definition for each of the
following terms: synthesis reaction and decomposition
reaction.
• 2. What type of reaction does the following equation
represent? FeS + 2HCl -> FeCl2 +H2S
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A. synthesis reaction
B. double-displacement reaction
C. single-replacement reaction
D. decomposition reaction
• 3. Describe the difference between single- and doubledisplacement reactions.
• 4. Write the balanced equation in which potassium iodide, KI,
reacts with chlorine to form potassium chloride, KCl, and
iodine.
Section 4 Review
• 1. Make the following TRUE: An exothermic reaction absorbs
energy.
• 2. Make the following TRUE: The rate of a reaction can be
increased by adding an inhibitor.
• 3. Which of the following will not increase the rate of a
reaction?
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A. adding a catalyst
B. increasing the temperature of the reaction
C. decreasing the concentration of reactants
D. grinding a solid into powder
• 4. How does the concentration of a solution affect the rate of
the reaction?