REaction Rates and REaction Rates and Equilibrium Equilibrium How Fast and How Far
Dec 30, 2015
REaction Rates and REaction Rates and EquilibriumEquilibrium
REaction Rates and REaction Rates and EquilibriumEquilibrium
How Fast and How FarHow Fast and How Far
ObjectivesObjectives
To understand collision model of chemical reactions
To understand activation energy
To understand how a catalyst speeds up a reaction
To explore reactions with reactants or products in different phases
To learn how equilibrium is established
To learn about characteristics of chemical equilibrium
To understand collision model of chemical reactions
To understand activation energy
To understand how a catalyst speeds up a reaction
To explore reactions with reactants or products in different phases
To learn how equilibrium is established
To learn about characteristics of chemical equilibrium
How Chemical reactions occurHow Chemical reactions occur
Molecules react by colliding with each other
Reactions go faster if concentration is increased
Reactions go faster with increased temperature
Molecules react by colliding with each other
Reactions go faster if concentration is increased
Reactions go faster with increased temperature
Conditions affecting reaction ratesConditions affecting reaction rates
Concentration - more molecules lead to more collisions
Why temperature?
Collisions must have enough energy to break bonds
Minimum energy to break bonds = activation energy
Concentration - more molecules lead to more collisions
Why temperature?
Collisions must have enough energy to break bonds
Minimum energy to break bonds = activation energy
Temperature and Reaction rateTemperature and Reaction rate
Higher
Temp
Higher
Temp
Higher
Speed
Higher
SpeedMore High-
energy Collisions
More High-
energy Collisions More bond
breakageMore bond breakage
Faster ReactionFaster Reaction
Reaction mechanismReaction mechanism
Step by step sequence of elementary reactions by which an overall chemical change occurs
For example: CO + NO2 --> CO2 + NO
The reaction mechanism for this might be:
2NO2 --> NO3 + NO (slow)
NO3 + CO --> NO2 +CO2 (fast)
Each step has its own rate
Rate of overall reaction is limited by rate of slowest reaction mechanism step
Step by step sequence of elementary reactions by which an overall chemical change occurs
For example: CO + NO2 --> CO2 + NO
The reaction mechanism for this might be:
2NO2 --> NO3 + NO (slow)
NO3 + CO --> NO2 +CO2 (fast)
Each step has its own rate
Rate of overall reaction is limited by rate of slowest reaction mechanism step
CatalystsCatalysts
Change reaction rate without changing temperature or concentration
Enzymes in your body are catalysts
Provides new pathway for reaction - lowers activation energy
Catalyst not used up in reaction
Change reaction rate without changing temperature or concentration
Enzymes in your body are catalysts
Provides new pathway for reaction - lowers activation energy
Catalyst not used up in reaction
How do catalysts work?How do catalysts work?
They increase the rate of effective collisions
How? Two main ways:
Help provide proper orientation of molecules so collisions “work”
Provide an alternate reaction mechanism that requires lower activation energy
Catalyst not used up or changed = can go on to catalyze more reactions
They increase the rate of effective collisions
How? Two main ways:
Help provide proper orientation of molecules so collisions “work”
Provide an alternate reaction mechanism that requires lower activation energy
Catalyst not used up or changed = can go on to catalyze more reactions
Catalyst exampleCatalyst example
Ozone Layer Destruction
Ozone absorbs high-energy radiation from the sun (e.g. UV light)
O + O3 --> 2O2
Chlorine catalyzes the reaction
One chlorine atom can catalyze the destruction of 1 million ozone molecules/second
Chlorine in the atmosphere from pollution by certain molecules called chlorofluorocarbons (e.g. CF2Cl2 - freon)
Ozone Layer Destruction
Ozone absorbs high-energy radiation from the sun (e.g. UV light)
O + O3 --> 2O2
Chlorine catalyzes the reaction
One chlorine atom can catalyze the destruction of 1 million ozone molecules/second
Chlorine in the atmosphere from pollution by certain molecules called chlorofluorocarbons (e.g. CF2Cl2 - freon)
EQUILIBRIUMEQUILIBRIUM
The exact balancing of two processes, one of which is the opposite of the other
For example - Physical equilibrium - Gas vaporizing over a liquid and gas condensing into liquid
H2O(g) <--> H2O(l)
This is a reversible process, indicated by double arrow
Equilibrium is reached when both processes are occurring at the same rate
The exact balancing of two processes, one of which is the opposite of the other
For example - Physical equilibrium - Gas vaporizing over a liquid and gas condensing into liquid
H2O(g) <--> H2O(l)
This is a reversible process, indicated by double arrow
Equilibrium is reached when both processes are occurring at the same rate
Chemical EquilibriumChemical Equilibrium
2NO2 (g) <--> N2O4 (g)
Dynamic Condition (process always happening)
Analogy - rate of cars leaving (reverse reaction) island on bridge = rate of cars arriving (forward reaction) on island on bridge - # of cars on island remains the same
Concentration of reactants and concentration of products remain the same indefinitely as long as the conditions are not changed
2NO2 (g) <--> N2O4 (g)
Dynamic Condition (process always happening)
Analogy - rate of cars leaving (reverse reaction) island on bridge = rate of cars arriving (forward reaction) on island on bridge - # of cars on island remains the same
Concentration of reactants and concentration of products remain the same indefinitely as long as the conditions are not changed
QuestionsQuestions
What must happen for two molecules to react together?
Name two factors that affect the rate of a reaction.
What is a catalyst? Give an example.
How do catalysts increase the rate of a reaction?
Define equilibrium. Give an example of physical equilibrium. Give an example of chemical equilibrium.
What must happen for two molecules to react together?
Name two factors that affect the rate of a reaction.
What is a catalyst? Give an example.
How do catalysts increase the rate of a reaction?
Define equilibrium. Give an example of physical equilibrium. Give an example of chemical equilibrium.
What if conditions Change?What if conditions Change?
Le Chatelier’s PrincipleLe Chatelier’s Principle