Holt Science amp Technology Physical Science Chapter 14 Chemical Reactions Section 4 Energy and Rates of Reactions Section Outline Reactions and Energy Exothermic reactions Figure 1 Types of Chemical Reactions ID: 574105
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Slide1
Using Chemical Demonstrations to Demonstrate Concepts in Physical Science IISlide2
Holt Science & Technology:Physical ScienceSlide3
Chapter 14 Chemical ReactionsSection 4 Energy and Rates of Reactions
Section Outline
Reactions and Energy
- Exothermic reactions
Figure 1. Types of Chemical Reactions
-Law of Conservation of Energy
Figure 2. No title
Rates of Reaction
- Activation energy
Figure 3. No title
-Sources of Activation Energy
Figure 4. Energy Diagrams
Slide4
Chapter 14 Chemical ReactionsSection 4 Energy and Rates of Reactions
Section Outline (cont.)
Factors Affecting Rate of Reaction
- Temperature
Figure 5. No title
- Concentration
Figure 6. Concentration of solutions
- Catalyst
Figure 7. No title
Slide5
Reactions and EnergyChemical energy is part of all chemical reactions.
Energy is needed to break chemical bonds in reactions.
Energy is released when new chemical bonds form in chemical reactions.
Slide6
Reactions and EnergyExothermic reaction – a chemical reaction that releases energyExo
means “go out” or “exit”
Endothermic reaction – a chemical reaction that takes energy in
Endo
means “go in”Slide7
Demonstration 1 – Energy Release
Types of Energy release
Light
Electrical energy
Light and thermal energySlide8
Demonstration 1 – LightSnapping a glowstick
breaks a small glass container in the
glowstick
, allowing chemicals in the glass container to mix with chemicals outside the glass (but inside the chamber of the
glowstick
).
The resulting reaction gives
off light.Slide9
Demonstration 2 – Electrical Energy
Electrical energy is released in an
exothermic reaction that takes place
in the battery
See if the batteries get warm.
2 MnO
2
(s) + 2 H
2
O(l) + Zn(s)
2
MnO
(OH)(s) +
Zn(OH)
2(s)Slide10
Demonstration 3 – Heat and Light Release
CH
4
+ 2 O
2
CO
2
+ 2 H
2
O
Energy is released during some chemical reactions. The fire of a Bunsen burner gives off light energy and chemical energy. (An alcohol burner, candle, lighter, etc. could also be used, although reaction would change.)
Slide11
Signs of Chemical ReactionsGas formationSolid (precipitate) formation
Color change
Energy change
Light
Thermal energy (heat)
Electrical energySlide12
Law of Conservation of EnergyLaw of conservation of energy – energy cannot be created or destroyed
Energy can change forms
Energy can be transferred from one
object to another in the same manner
that a baton is transferred from one
runner to another in a relay race.Slide13
Rates of ReactionActivation energy – smallest amount of energy that molecules need to react.
Chemical reactions need energy to get started
In the same way that a bowling ball needs a push
to get rolling.Slide14
Activation Energy
Reaction progress
Reaction progress
Products
Energy
given
off
Energy
Reactants
Activation energy
Energy
Energy
absorbed
Activation
energySlide15
Factors Affecting Rates of ReactionDemonstration 4 – Glow Sticks
Temperature
A higher temperature causes a faster reaction rate.
At higher T, particles of reactants move rapidly.
Rapid movement causes particles to collide often and with a lot of energy.
Many particles have the activation energy to react and change into products in a short time.
The light stick on the right glows brighter
than the one on the left because the one
on the right is warmer. Slide16
Factors Affecting Rates of Reaction
Concentration
In general, a high concentration of reactants causes a fast rate of reaction.
Concentration is a measure of the amount of one substance dissolved in another substance.
When the concentration is high, there are many reactant particles in a given volume and a small
distance between them.
Thus, the particles run into each
other often, leading particles to react faster.Slide17
Factors Affecting Rates of Reaction
Surface Area
Surface area is the amount of exposed surface of a substance
Increasing surface area increases rate of reaction.
Greater surface area exposes more particles of the reactant to other reactant particles.
These leads to more collisions and faster rates.Slide18
Demonstration 5 – Mentos and Diet Coke
http://www.eepybird.com/featured-video/the-extreme-diet-coke-mentos-experiments-ii-the-domino-effect//Slide19
Factors Affecting Rates of Reaction
Inhibitors
An inhibitor is a substance that slows down or stops a reaction
Food preservatives – slow down growth of bacteria and fungiSlide20
Factors Affecting Rates of Reaction
Catalysts
Catalyst – speeds up a chemical reaction without being consumed/
A catalyst is not consumed because it is not a reactant.
A catalyst lowers the activation barrier, which allows a reaction to happen more quickly.
This catalytic converter contains platinum and
palladium. These two catalysts increase the rate
of reactions that make the car’s exhaust less
harmful.Slide21
Demonstration 6 – CatalystHydrogen peroxide, H
2
O
2
, is unstable but decomposes very slowly. The decomposition reaction gives off heat. If Cu
2+
ions are added (as a catalyst) to add aqueous solution of H
2
O
2
, the reaction proceeds rapidly and can become hot enough to boil the water.
If dishwashing detergent is added to the solution before the catalyst, then a version of the elephant toothpaste demonstration is produced.
2 H
2
O2 O2 + 2 H2O Slide22
Demonstration 7 – Clock ReactionConcentration, temperature, inhibitorSlide23
Demonstration 8 – Alka Seltzer
Concentration, temperature, surface area