Download Collision Theory

AP CHEMISTRY TUTORIALS–09
AP QUESTIONS
Srinivasan G. Srivilliputhur
February 24, 2016
Today’s Overview
1
• Review: Chemical Kinetics
2
• AP Examples
1
• Review: Chemical Kinetics:
Collision Theory
Reaction Kinetics: study of the factors that
affect the rates of chemical reactions
Collision Theory Summary
• Molecules must collide to react
• Main Factors:
 Activation energy, Ea
 Temperature
 Molecular orientations
5
Theories of Chemical Kinetics: Collision Theory
• Before atoms/molecules/ions can react, they must first collide
• An effective collision between two species puts enough energy
to break key bonds
• The activation energy (Ea) is the minimum energy that must
be supplied by collisions to trigger a reaction
• A certain fraction of all molecules in a sample will have the
necessary activation energy to react
• Fraction of molecules that will react increases with increasing
temperature. (General rule: 10° (Celsius/Kelvin) increase
doubles rate)
• The spatial orientation of the colliding species often determine
whether a collision is effective.
6
Reactant and Product Concentrations as a
Function of Time: H2 (g) + I2 (g)  2 HI (g)
Using [H2]:
instantaneous rate at 50s:
Using [HI]:
instantaneous rate at 50s:
Plots Rate vs. Concentration
Rate = k[A]n
Rate constant ‘k’
likely changes with:
• Temperature
• Catalysts
Enzymes are
biocatalysts
Plots Rate vs. Concentration
Rate = k[A]n
Rate constant ‘k’
likely changes with:
• Temperature
• Catalysts
2
• AP 2015 FRQ #5
2015 AP® CHEMISTRY FREE-RESPONSE QUESTIONS
Compound
Melting Point (degrees celsius)
LiI
449
KI
686
LiF
845
NaF
993
6. A student learns that ionic compounds have significant covalent
character when a cation has a polarizing effect on a large anion.
As a result, the student hypothesizes that salts composed of
small cations and large anions should have relatively low melting
points.
(a) Select two compounds from the table and explain how the
data support the student’s hypothesis.
(b) Identify a compound from the table that can be dissolved in
water to produce a basic solution. Write the net
ionic equation for the reaction that occurs to cause the solution to
be basic.