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Reaction Rates and Equilibrium

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by

Jennifer Wong

on 22 April 2014

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Transcript of Reaction Rates and Equilibrium

Essential Question
Reaction Rates
Collision Model
Molecules must COLLIDE to react

What determines an
effective collision
?
Enough
kinetic energy
in the molecules
Proper
orientation
of the molecules
Reaction Energy Diagram
What does the activation energy tell us about a reaction?
What does the energy change tell us about the reaction?
Exothermic
reaction: reactants are
higher
in energy than products
negative
energy change (- H)

Endothermic
reaction: reactants are
lower
in energy than products
positive
energy change (+ H)
Reaction Rates
What are reaction rates?
Speed of any change that occurs within an interval of time
How do we calculate the rate?
the amount of reactant changing per unit of time
What does it tell us?
Fast rate: change occurs quickly (like a firecracker or explosion)
Slow rate: change occurs slowly (like plant matter decaying to make coal)
Activation Energy (Ea)
is

t
he minimum energy required to react
height of the hill from reactants to peak
Reactants
Products
Activated Complex (aka transition state)
is an unstable arrangement of atoms that forms momentarily at the
peak
of the activation-energy barrier

What can happen next?
form the product
reform the reactants
Energy Change ( H)

of overall reaction
High Ea
= less probable (
slow
) reaction

Low Ea
= more probable (
fast
) reaction

How can we affect reaction rate?
1. Temperature
Direct
relationship
At higher temperatures, reactants are moving faster and have more energy
Number of collisions increases
Number of particles that have enough kinetic energy to climb the activation energy barrier increases
Reaction rate increases

How can we affect reaction rate?
2. Surface Area
Direct
relationship
Increasing surface area means there are more places for reactants to collide
Number of collisions increase
Number of collisions with proper orientation increases
Reaction rate increases
How can we affect reaction rate?
3. Concentration
Direct
relationship
Increasing number of particles in a given volume, increases concentration
Number of collisions increase
Reaction rate increases
How can we affect reaction rate?
4. Presence of a catalyst
Catalyst
: substance that speeds up the reaction
remains
unchanged
by reaction
lowers
activation energy (Ea)
Biological catalyst (usually a large protein) is called an
enzyme











Inhibitor
: interferes with the action of the catalyst
slows or stops reaction
How does the activation energy play a role in the reaction rate?
Chapter 18
Essential Question
How do temperature, surface area, concentration, and the presence of a catalyst affect reaction rates?
Joule is a unit of heat
1000 Joule (J) = 1 kiloJoule (kJ)
Sketch an energy diagram for the
exothermic
reaction:
Practice #1
Warm Up
Practice #2
Sketch an energy diagram for the
endothermic
reaction
Wed 04.23.14
Full transcript