KINETICS AND EQUILIBRIUM. BELL RINGER How can you make a reaction occur quicker?
70
KINETICS AND EQUILIBRIUM
-
Upload
andrew-grant -
Category
Documents
-
view
214 -
download
0
Transcript of KINETICS AND EQUILIBRIUM. BELL RINGER How can you make a reaction occur quicker?
KINETICS AND EQUILIBRIUM
BELL RINGERHow can you
make a reaction occur quicker?
- The study of reaction rates and their relation to the way the reaction
proceeds, ie. its mechanism
A REACTION is the _________ and ____________ to make entirely new
compounds as products
breaking re-forming
Kinetics
Step by step process needed to make a product
Reaction Mechanism
How to get from a b
Reactants Products
Just like making a recipe!
o Can’t omit steps
o Can’t change the order of the steps
o Can’t omit any reactants
Determine if the following chemical reactions would be considered slow or fast:
Some Practice
Rusting
Alka Seltzer in water
Styrofoam decomposing
Weathering of rocks
Bleaching fabric
1. Number of steps
What determines the rate of a reaction?
more steps mean a slower rxn
= slowest step of the rxn
- the MOST important factor in determining the rate
A + B + C ABC (2 steps)
2. Rate determining step
Tall hill
Short hill
Collision Theory“You can’t react if you don’t collide!”
Bumper cars – need to get bumped out of your seat – going fast enough
Collision Theory“You can’t react if you don’t collide!”
1. Proper orientation
Side collisions just move you, need to hit head on for the bonds to be broken and new bonds be formed
A2 + B2 2AB
Collision Theory“You can’t react if you don’t collide!”
2. Speed
Particles need to have enough speed when they collide.
They need that MINIMUM amount of energy
Activation Energy
Ea
Collision TheorySummary
1. Particles collide with the correct orientation
CAR ACCIDENT
Click here!
Successful collisions occur only when:
2. Particles collide with enough speed
CAR ACCIDENT
#2
Click here!
Motorcycle’s
Some Kinetics Terminology
Rate
Velocity (speed) at which a reaction occurs
Kinetics
How fast a reaction occurs and the mechanism by which it occurs
Activation Energy
Amount of energy needed to “kick-start” a reaction
Example: A match will not light on its own, the match must have an addition of mechanical
energy (striking the box) so it will light
Demo: Balloon
Ea
You can make reactions go faster by changing…
Temperature
Concentration
Particle Size
Nature of Reactants
Catalysts
Pressure
“Make more collisions”
You can make reactions go faster by…
Temperature
Increase“Make more collisions”
Particles moving faster = more likely to collide
Increased speed = greater force of the collisions
You can make reactions go faster by…
Concentration Increase
“Make more collisions”
More particles = More collisions
“Crowded Space”
You can make reactions go faster by…
Particle Size
Decrease
“Make more collisions”
Also known as Surface Area
Making the particles smaller, ↑ SA
↑ SA → increases chance for effective collisions
vs
You can make reactions go faster by…
Nature of Reactants Ionic are faster
“Make more collisions”
You can make reactions go faster by…
CatalystsLower Ea
“Make more collisions”
Def – a substance that increases the rate of reaction without being used up
It lower the Ea, lowers the activated complex, and/or reaction pathway is shortened
Makes collisions easier to occur
You can make reactions go faster by…
Pressure
“Make more collisions”
Increase (Only gases)
You can make reactions go faster by…
Temperature
Concentration
Particle Size
Nature of Reactants
Catalysts
Pressure
Ionic are faster
Increase
Decrease
Increase
Lower Ea
“Make more collisions”
Increase (Only gases)
Heat of Reaction
ΔHThe difference between the potential energy of the products and the potential energy of the reactants
ΔH = Hproducts – Hreactants
PE(KJ)
Reaction coordinate
PE of reactants
PE of products
H
PE of products
Ea
PE of activated complex
Activated complex
Occurs when reactants collide in the proper orientation
Very unstable, only lasts a momentQuickly moves to products
Bonds are in the process of breaking and forming
BELL RINGERID the letters below:
PE(kJ)
Reaction coordinate
PE of reactants
PE of products
H
PE of products
Ea
Ea with a catalyst
Catalyst - Compound which lowers Ea
Is not permanently changed in the reaction
Can be reused
Does not change the H
EndothermicΔH = Hp - Hr
ΔH = 300 - 100 = 200 ΔH is always +
ExothermicΔH = Hp - Hr
ΔH = 50 - 150 = -100ΔH is always -
BELL RINGERGiven the following balanced equation:
N2(g) + O2(g) + 182.6 kJ 2NO(g) Draw the potential energy diagram below.
Reaction Coordinate
Po
tential E
nerg
y
Reversible Reaction Some reactions can run back to reactants
A + B AB A + B AB
PE(kJ)
Reaction coordinate
A + B
AB
FWD
Eaf
RVS
Ear
Reactions are opposite
One is exothermic, one is endothermic!
H is the same, but has opposite signs
H
EquilibriumThe following conditions must be met:
•Can only be reached in a closed system
•Rate forward rxn = Rate reverse rxn
•Concentration of each solution is constant
•Saturated Solutions are at equilibrium
B A B A B A B A BA B
B A A A A A B A B
B A A B A
B A B
First only the forward reaction occurs
There is no product to run the reverse reaction
C
C
C
Cforward
forward
forward
forward
A + B --> C
Click to go to next scene
A. Establishing
Click the mouse to watch the forward reaction begin
Equilibrium
As the [products] increases, some products begin to change back to reactants
This is the start of the reverse reaction
B A B A B A B A BA B
B A A A A A B A B
B A A B A
B A B
C
C
C
Cforward
forward
forward
forward
A B
Reverse
A B
Reverse
C A + B
Click to go on
Equilibrium
Eventually, the RATE of the forward reaction equals the rate of the reverse reaction
B A B A B A B A BA B
B A A A A A B A B
B A A B A
B A B
C
C
C
Cforward
forward
forward
forward
A B
Reverse
A B
Reverse
A B
Reverse
Cforward
This is Dynamic Equilibrium
Equilibrium - When the rate of the forward reaction is equal to the rate of the reverse reaction
Cforward
A B
Reverse
Concentration of products and reactants do not change
Amount of products do not usually equal the amount of reactant
Did you notice that we always have the same amount of products and reactants?
Click to go onDid you also notice that we have way more reactants than products?
Equilibrium
Equilibrium only occurs when the rate of the forward reaction equals the rate of the reverse reaction
At equilibrium the amount of reactants do not equal the amount of products
At equilibrium, the concentration of reactants and products do not change
The reverse reaction only begins when enough product has been created
Equilibrium
BELL RINGERWhat is the value for the activation energy?
What is the heat of reaction?
Types of equilibriums(must be in closed systems)
1. Physical Equilibrium: - involves a physical change
a. Phase equilibrium – occurs during a phase change
(s) ↔ (l)(l) ↔ (g)
RATE of Melting = Rate of Freezing
RATE of Evaporation = Rate of Condensation
b. Solution equilibrium – at a solution’s saturation point
RATE of dissolving = Rate of crystallization
Example NaCl(s) ↔ NaCl(aq)
Types of equilibriums(must be in closed systems)
2. Chemical Equilibrium:
RATE of forward rxn = Rate of reverse rxn
RATE of breaking bonds = Rate of forming bonds
H2(g) + I2(g) + 53.0 kJ ↔ 2 HI(g)
Notice the concentrations are
not equal, but constant
LeChatelier’s Principle‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’
How a system at equilibrium will respond to stress
STRESS - any change in temperature, concentration, or pressure put on a system at equilibrium
When a STRESS is added to a system at equilibrium, the system will shift in order to relieve that stress and reach a new equilibrium.
SHIFT = An increase in the RATE of EITHER the forward OR reverse rxn
LeChatelier’s Principle‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’
SHIFT = an increase in the RATE of EITHER the forward OR reverse rxn
SHIFT TO RIGHT toward the products
Rate of the FORWARD reaction INCREASES
REACTANTS PRODUCTS
SHIFT TO LEFT toward the reactants
Rate of the REVERSE reaction INCREASES
PRODUCTSREACTANTS
LeChatelier’s Principle‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’
General Ideas:
• If a concentration, temperature, or gas pressure is increased, the reaction shifts away from the increase in order to use up the extra & re-establish equilibrium.
• If a concentration, temperature, or gas pressure is decreased, the reaction shifts toward the decrease in order to replace what was removed & re-establish equilibrium.
AA – what you ADD causes a shift AWAY
TT– what you TAKE causes a shift TOWARDS
LeChatelier’s Principle‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’
SIMULATION
LeChatelier’s Principle‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’
Stress: Increased
2SO2(g) + O2(g) ↔ 2SO3(g) + Heat
Increase [SO2]
Increase Temperature
Increase Pressure
LeChatelier’s Principle‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’
Stress: Decreased
2SO2(g) + O2(g) 2SO3(g) + Heat
Decrease [SO2]
Decrease Temperature
Decrease Pressure
LeChatelier’s Principle‘A dynamic equilibrium tends to respond so as to reduce the effect of an imposed change.’
CoCl(H2O)5 + Cl- + Heat ↔ CoCl2(H2O)2 + 3H2O
Warm Water
Cold Water
favors endo- Shifts Right
favors exo- Shifts Left
PINK BLUE
Add Water favors reverse
Shifts Left
BELL RINGERGiven the following reaction:
H2(g) + F2(g) 2 HF(g) + Heat
In terms of LeChatelier’s, what could you do to
increase the production of hydrogen fluoride?
Why do chemical/physical changes occur?
ENTROPY (ΔS) –degree of randomness or chaos or disorder or “messiness” in a system
- Nature tends to proceed to a state of greater entropy, or disorder
The MORE order you have, the LESS entropy in your system
The LESS order you have, the MORE entropy in your system
Why do chemical/physical changes occur?
A phase change is the most significant factor in determining ΔS
Increased entropy
Changing from
s l aq gDraw particle diagrams for each below
Entropy increases when a compound is broken downEntropy decreases when a compound is created and bonds are formed
Entropy ExamplesWhich of the following would you expect to have
a higher entropy?
Rock SoilAdult’s
BedroomTeenager’s bedroom
Ice WaterClouds Rain
Pure Water Saline
Old teachers Young dedicated students
EntropyWhich has higher entropy?
Begin Equilibrium
Lab
Le Chatelier’s Problems
A(s) + 2B(g) C(g) + 3D(g) + Heat Pressure increases
Pressure decreases
Rate of forward rxn
Rate of reverse rxn
[A]
[B]
[C]
[D]
I=increase D=decrease R=remains the same
D I
I D
I D
I D
D ID I
BELL RINGERUsing the graph below, identify a, b and c.
What is the value for H?
Does the forward or reverse reaction produce more stable products?
Common Ion Effect
Two different ionic compounds that have an ion in common:
NaCl and HCl
When these are mixed, the common ion is the stress because it increases the ion’s concentration, the reaction shifts away from the ions and the less soluble compound PPT out of solution to re-establish equilibrium
NaCl Na+ + Cl-
EnthalpyAll matter has energy stored in it. Either as a
chemical bond, or as kinetic energy.
Enthalpy total energy of a substance
Includes chemical energy, phase and KE
Very difficult to measure, but we can measure the change in enthalpy = H
EnthalpyAs a way to measure the stability of a compound
Most stable compoundsH high negative numberBecause it would take a lot of energy to reverse the reaction
Least stable compoundsH positive, or low negative numberBecause it would not take a lot of energy to reverse the reaction
With the help of Table I, which compound would be the most stable?
NH3 or Al2O3
Table I: Heats of Reaction
ΔH – tells how much energy is given off/absorbed
N2(g) + O2(g) 2NO(g)
To make one mole of NO, how much energy must be absorbed?
ΔH = 182.6kJ
Table I: Heats of Reaction
Is the production of aluminum oxide endothermic or exothermic?
ΔH = -3351kJ, so exothermic
When you dissolve NaOH in water, does the water get warmer or colder?
ΔH =-44.51
Therefore it is exothermic, the water will get warm
Natural Lawthe course of a reaction
• Reactions occur to form more stable products (essentially increasing stability)
1. The reaction releases energy:
EXOTHERMIC; -H, stability
2. The reaction increases entropy
entropy, stability
Equilibrium only occurs when the rate of the forward reaction equals the rate of the reverse reaction
At equilibrium the amount of reactants do not equal the amount of products
At equilibrium, the concentration of reactants and products do not change
The reverse reaction only begins when enough product has been created
Equilibrium
• Trash Talk Harm me with harmony.Doomsday, drop a load on 'em.
Verse 1 Entropy, how can I explain it? I'll take it frame by frame it,to have you all jumping, shouting saying it.Let's just say that it's a measure of disorder,in a system that is closed, like with a border.It's sorta, like a, well a measurement of randomness,proposed in 1850 by a German, but wait I digress."What the **** is entropy?", I here the people still exclaiming,it seems I gotta start the explaining.
You ever drop an egg and on the floor you see it break?You go and get a mop so you can clean up your mistake.But did you ever stop to ponder why we know it's true,if you drop a broken egg you will not get an egg that's new.
That's entropy or E-N-T-R-O to the P to the Y,the reason why the sun will one day all burn out and die.Order from disorder is a scientific rarity,allow me to explain it with a little bit more clarity.Did I say rarity? I meant impossibility,at least in a closed system there will always be more entropy.That's entropy and I hope that you're all down with it,if you are here's your membership.
Chorus You down with entropy?Yeah, you know me! (x3)Who's down with entropy?Every last homey!
•Verse 2 Defining entropy as disorder's not complete,'cause disorder as a definition doesn't cover heat.So my first definition I would now like to withdraw,and offer one that fits thermodynamics second law.First we need to understand that entropy is energy,energy that can't be used to state it more specifically.In a closed system entropy always goes up,that's the second law, now you know what's up.
You can't win, you can't break even, you can't leave the game,'cause entropy will take it all 'though it seems a shame.The second law, as we now know, is quite clear to state,that entropy must increase and not dissipate.
Creationists always try to use the second law,to disprove evolution, but their theory has a flaw.The second law is quite precise about where it applies,only in a closed system must the entropy count rise.The earth's not a closed system' it's powered by the sun,so **** the damn creationists, Doomsday get my gun!That, in a nutshell, is what entropy's about,you're now down with a discount.
Chorus
Trash Talk Hit it!Doomsday, kick it in!
Entropy
BELL RINGERIn the following reaction what can you
do to increase the production of ammonia?
N2(g) + 3H3(g) 2NH3(g) + heat
BELL RINGERUse the collision theory to
explain why food is refrigerated.
Quiz
RB – p136-150
q. 1-44
In pairs
EXAM
Le Chatelier’s Problems
A(g) + 2B(g) C(g) + D(g) Moles of B Moles of B
Rate of forward rxn
Rate of reverse rxn
[A]
[C]
[D]
I=increase D=decrease R=remains the same
I D
D ID I
I D
I D
Le Chatelier’s Problems
A(g) + B(g) + Heat C(g) + D(g)
Temperature increases
Temperature decreases
Rate of forward rxn
Rate of reverse rxn
[A]
[B]
[C]
[D]
I=increase D=decrease R=remains the same
I D
D I
D I
D I
I DI D
BELL RINGER
How can you tell that the system was at equilibrium in the beginning and then re-
established a new equilibrium?
BELL RINGER1. CO + O2 CO2 + 393.5kJ
2. H2 + I2 2HI H = 53.0 kJ
3. N2 + 2O2 + 66.4 kJ 2NO2
4. H+ + OH- H2O H = -55.8 kJ
Of the above 4 reactions, which one produces the most stable products?
