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Kinetics(Reaction Rate)
How Fast Does the Reaction Go
Collision Theory In order to react molecules and atoms
must touch each other.They must hit each other with enough
force and with the correct orientation.The more “frequently” the particles hit,
the faster the reaction will go.Anything that increase these
effective collisions will make the reaction faster.
Factors that Affect RateTemperature
– Higher temperature faster particles.– More and harder collisions.– Faster Reactions.
Concentration– More concentrated closer together the
molecules.– Collide more often.– Faster reaction.
Factors that Affect Rate Particle size
– Molecules can only collide at the surface.– Smaller particles bigger surface area.– Smaller particles faster reaction.– Smallest possible are molecules or ions.
Dissolving speeds up reactions.– Getting two solids to react with each
other is slow.
Factors that Affect RateCatalysts- substances that speed up a
reaction without being used up.(enzyme).– Speeds up reaction by giving the
reaction a new path.– The new path has a lower activation
energy.– More molecules have this energy.– The reaction goes faster.
Inhibitor- a substance that blocks a catalyst.
Potential Energy Diagrams
Represent the changes in potential energy that occur during a chemical reaction.
The reaction coordinate represents the progress of the reaction.
Remember in terms of energy content
HIGH ENERGY =UNSTABLELOW ENERGY = STABLE
Classification of reactions
Exothermic Rx: releases energy. Heat part of the products.
Endothermic Rx: absorbs energy. Heat part of the reactants.
DefinitionsActivation Energy: the minimum amount
of energy needed to start up a chemical reaction.
Activated Complex: a temporary
intermediate product. Highest point of the diagram. Is UNSTABLE.
Catalyzed Reactions
Need less energy to start up the reaction. The presence of a catalyst LOWERS THE ACTIVATION ENERGY!!!
Ene
rgy
Reaction coordinate
Reactants
Products
Ene
rgy
Reaction coordinate
Reactants
Products
Activation Energy - Minimum energy to make the reaction happen
Ene
rgy
Reaction coordinate
Reactants
Products
Activated Complex or Transition State
Ene
rgy
Reaction coordinate
Reactants
Products
Overall energy change (H)
Thermochemistry
The study of the changes in heat energy that accompany chemical reactions and physical changes.
What is H?
H is the enthalpy, or
“heat of reaction.” The amount of energy released or absorbed during a chemical reaction.
By convention
Hrxn = Hproducts - Hreactants
What is an exothermic reaction?
A reaction that gives off or releases heat.
Since...
Hrxn = Hproducts - Hreactants
then Hrxn will be a negative number
Ene
rgy
Reaction coordinate
Reactants
Products
Overall energy change (H)
What is an endothermic reaction?
A reaction that absorbs heat.
Since…
Hrxn = Hproducts – Hreactants
then H will be a positive number.
Energy
Reaction coordinate
Reactants
Products
Overall energy change (H)
Heats of Reaction Table IThe new reference table (Table I) shows different heats of reaction for some common reactions.
EXOTHERMIC RXRelease heat.H for reaction is negativeThe value for H is the amount of heat
released during the rxWe write the heat it as PRODUCT in the
chemical equationThe greater the magnitude of H the
more stable the product will be!!!!
Absorb heatH for reaction is positiveThe value for H is the amount of heat
absorbed during the rxWe write the heat it as REACTANT in the
chemical equationThe greater the magnitude of H the
more UNstable the product will be!!!!
ENDOTHERMIC RX
PAGE 140 ANSWERS RB 2012 edition11. 4
12. 2
13. 1
14. 2
15. 2
16. 1
17. 3
INTERPRETING REACTION COORDINATES handout
1) B
2) A
3) G
4) G
5) A
6) F
7) F
8) F
9) F
10) B
11) E
12) I
13) D
14) J
15) C
16) H
17) H
18) A
PE DIAGRAMS FOR RX 1. EXO
2. -30
3. 20
4. 10
5. 60
6. ENDO
7. 25
8. 20
9. 30
10. SAME
11. H
12. E
13. B
14. G
15. I
16. F
17. A
18. C
19. D
HEATS OF REACTION MC1) 1
2) 1
3) 4
4) 2
5) 2
6) 2
7) 2
8) 1
9) 1
10) 4
11) 4
12) 1