Grade 8 Integrated Science Chapter 9 Lesson 3 on energy changes and chemical reactions. An introduction to conservation of mass, endothermic and exothermic reactions, activation energy, and potential energy graphs.

1. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 1
Vocabulary
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endothermic (319) – Chemical reactions that absorb thermal energy
exothermic (319) – Chemical reactions that release thermal energy
activation energy (320) – the minimum amount of energy needed to start a chemical reaction
catalyst (322) – a substance that increases reaction rate by lowering the activation energy of a reaction
enzyme (322) – a catalyst that speeds up chemical reactions in living cells
inhibitor (322) – a substance that slows, or even stops, a chemical reaction
Energy Changes
 To propel a space shuttle, scientists use rocket fuel.
 The shuttle’s main engines burn almost 2 million L of liquid hydrogen and liquid oxygen.
 The reaction produces water vapor and a lot of ______________________.
 The ___________________energy causes the water vapor to heat to high temperatures.
 The rapidly expanding water vapor pushes the shuttle.
Chemical Energy in Bonds
 Chemical _______________ contain a form of energy called chemical energy
o Breaking a bond _______________ energy from the surroundings.
o The formation of a bond _________________energy to the surroundings.
o Some chemical reactions release more energy then they absorb.
o Others absorb more than they __________________.
o You can detect these energy changes by recording the _______________________of
the surroundings.
Endothermic Reactions – Energy Absorbed
 Chemical reactions that absorb thermal energy are ___________________ reactions
 For an endothermic reaction to continue, __________________must be constantly added.
 In these reactions _______________________energy is required to break bonds of the
reactant than is released when the products form.
 Therefore, the overall reaction _______________________ energy.
Draw an energy diagram for an endothermic rxn.

2. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 2
Exothermic Reactions – Energy Released
 An ___________________reaction is a chemical reaction that releases thermal energy
 In an exothermic reaction, more energy is ____________________when the products form
than is required to break the bonds in the reactants.
 Therefore, the overall reaction _________________energy
Draw an energy diagram for an exothermic rxn.
Activation Energy
 Many reactions do not start by______________________________.
o Paper does not burn when it touches oxygen. _________________is required.
 All reactions require _______________________ to start the breaking of bonds.
 This is called ______________________ energy.
 Activation energy is the ______________________________amount of energy needed to start
a chemical reaction.
o Different reactions require __________________________activation energies
 The rusting of iron is a reaction that has a _________________activation energy.
o The energy in the surroundings is enough to start the process.
 Other reactions require ___________ energy and have ____________ activation energy
o The burning of wood requires the energy of a flame.
o Once the reaction starts, the reaction itself ___________________ enough energy to
keep the reaction going.
Reaction Rates

3. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 3
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Some reactions happen quickly, while others happen very ______________________
o Fireworks explode in seconds
o The rate of reaction is the __________________________ at which it occurs.
For a chemical reaction to occur, particles must collide in the right _____________________
with enough energy to _________________ the bonds
o Chemical reactions occur faster of particles collide more often or move faster when
they collide.
Several Factors Affect Reaction Rates
 ___________________________________
 ____________________________________
 Concentration and Pressure
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 Inhibitors
Surface Area
 Surface area is the amount of ______________________, outer area of a solid.
 Increased surface area increases reaction rate because more _________________________ on
the surface if a solid come into contact with the particles of another substance.
o Consider a piece of chalk versus the same amount of chalk powder.
Temperature

4. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 4
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At higher temperatures, the average __________________________of particles is greater
This speeds reactions in two ways
o First, particles _____________________ more often
o Second, collisions with more _________________________ are more likely to break
chemical bonds
Concentration and Pressure
 Increasing the ________________________________of one or more reactants increases
collisions between particles.
 More collisions results in a faster reaction rate.
 In gases an increase in _________________________________ pushes gas particles closer
together
 When they are close, more collisions occur

5. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 5
Catalysts
 A catalyst is a substance that increases reaction rate by lowering the
__________________________energy of a reaction.
o One way catalysts speed reactions is by helping reactant particles
___________________________ each other more often
o A catalyst isn’t _______________________ in a reaction, and it doesn’t change the
reactants or products
o A catalyst doesn’t increase the amount of reactant used or the amount of product that
is made.
 Catalyst are not_______________________, so they are not considered reactants
 Your body is filled with catalysts called_______________________________.
 An enzyme is a catalyst that speeds up chemical reactions in living cells.
o The enzyme protease breaks the protein molecules that can be absorbed by your
intestine.
o Without protease the reaction would occur too slowly and we could
not_________________________.

6. Chapter 9.3: Energy Changes and Chemical Reactions – p317-323 – page 6
Draw an energy diagram of a catalyzed and uncatalyzed reaction.
Inhibitors
 An inhibitor is a substance that____________________________, or even stops, a chemical
reaction caused by an enzyme.
 Inhibitors are often used on our foods. ________________________________ are inhibitors
that slow the processes that cause food to spoil.