chemical equilibrium part 1 ch. 15 in textbook fanpop.com
TRANSCRIPT
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Chemical EquilibriumPart 1
Ch. 15 in Textbook
Fanpop.com
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I. Static vs. Dynamic
Generally speaking, an equilibrium is a state of balance.
A static equilibrium is one in which there is no motion.
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Wirednewyork.com
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A dynamic equilibrium is one in which there is motion despite there being no net change.
A chemical equilibrium is an example of a dynamic equilibrium.
Ene.on.gov.ca
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II. Chemical Equilibria
Suppose we have the gaseous reactants I2 and H2. They undergo a synthesis reaction to form HI:
H2 + I2 → 2HI As HI accumulates, some
molecules have enough energy to decompose to H2 and I2:
2HI → H2 + I2
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As this process continues, eventually the rate of the forward reaction equals the rate of the reverse reaction.
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Link
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The final equilibrium mixture will contain both reactants and products.
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Although the amounts are NOT necessarily equal, the amounts must eventually remain constant since the forward and reverse reactions are occurring simultaneously and at the same rate.
Mmsphyschem.com
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Although there is no noticeable net change in reactants or products, the reaction is still proceeding in the forward and reverse directions, making chemical equilibrium a dynamic equilibrium.
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HW: 15.2Tutorial
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III. Kinetics Flashback!!!!
Given: A B Assume that the
forward and reverse reactions are both elementary steps.
Rate (forward) = kf [A] Rate (reverse) = kr [B] At equilibrium: kf [A]
= kr [B]
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Rearranging: [B]/[A] = kf/kr = constant
What is the meaning of this?!
At a given temp. the products and reactants will ALWAYS be in the same ratio at equilibrium, no matter the starting point…
Blog.al.com
HW: 15.3
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IV. The Law of Mass Action
This proportion can be represented by the equilibrium expression.
The Law of Mass Action states that the equilibrium expression depends on the equilibrium concentrations of reactants and products.
Marcvallee.wordpress.com
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For the reaction:aA + bB pP + qQ
the equilibrium expressionis written as: K = [P]p [Q]q
[A]a [B]b
where K is the equilibrium
constant.Oudaily.com
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Ex) What is the equilibrium expression for the synthesis of hydrogen iodide?
Threadless.com
HW: 15.6, 15.20
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In KINETICS, the rate law did NOT depend on the stoichiometry of the net equation, only on the rate-determining step.
In EQUILIBRIUM, the equilibrium expression DOES depend on the stoichiometry of the net equation.
Efuse.com
Yes, typo
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V. The Equilibrium Constant, K,…
A) Dependence …does not depend on the
reaction mechanism. …does not depend on the
initial concentrations of reactants and products.
…depends on the equilibrium concentrations of reactants and products.
..also depends on temperature! (more on that later…)
We generally omit the final units.
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B) Magnitude
Since products are divided by reactants in the expression: A larger K value (>>1)
means that products dominate the final reaction mixture and we say “the equilibrium lies to the right.”
A smaller K value (<<1) means that reactants dominate the final reaction mixture and we say “the equilibrium lies to the left.”
Balthaus.org
HW: 15.10
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C) Kc
This is the constant when concentrations are expressed in molarity.
It is the most common version of K.
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D) Kp
This is the constant when concentrations (of gases) are expressed in terms of partial pressures (atm).
K = (PP) p (PQ)q
(PA)a (PB)bLankapeacewatch.com
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E) Relationship between Kc and Kp
Files.chem.vt.edu
Note: My notes are WAY better…this PowerPoint slide doesn’t even have a stupid picture in it…or a picture of another chemistry PowerPoint slide…of another PowerPoint Slide…of another PowerPoint slide…ad infinitum.
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E) Relationship between Kc and Kp (fo’ real dis time)
PV = nRT P = (n/V) RT For substance A:
PA = [A] RT Do this for all partial pressures in an
equilibrium mixture and we get: Kp = Kc (RT)Δn
where Δn is the moles of gaseous products -
the moles of gaseous reactants. Link
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Ex) Given: 2SO3(g) 2SO2(g) + O2(g)
Write the Kp expression.
Calculate Kp if Kc = 4.08 x 10-3 at 1000 K.
W3.org
HW: 15.8 (a) & (b), 15.12
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F) Direction
Equilibrium can be reached from any direction (all reactants or all products or any mixture of both).
Kc (forward) = 1/Kc (reverse)
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HW: 15.16
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Breakdancing Baby Break
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VI. Heterogeneous Equilibria
These involve one or more reactants or products present in a different phase.
Many equilibria do not involve dissolved species or gases.
The concentration of a pure solid or liquid is constant and therefore does not appear in the equilibrium expression.
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Ex) 3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)
Write the Kp expression.
Pig Iron from
Bbc.co.uk
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Thus, only the partial pressures of water and hydrogen affect the equilibrium expression.
Don’t forget though, the solids must be present in order for the equilibrium to be established.
Open.salon.com
HW: 15.18
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VII. Calculating K
Use an ICE chart: Initial, Change, and Equilibrium.
First, determine all initial concentrations.
Second, determine any available equilibrium concentrations.
Third, use the reaction stoichiometry to determine the change in concentration from the initial to equilibrium.
Burnblog.burningman.com
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Fourth, determine all equilibrium concentrations.
Fifth, plug and chug into equilibrium expression and find K. Nitrocotton.com
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Ex) 2SO3 (g) 2SO2(g) + O2(g)
A vessel at 1000 K contains 6.09 x 10-3
M SO3. At equilibrium, the SO3 concentration is 2.44 x 10-3 M. What is the value of Kc? Portlandsentinel.com
HW: 15.24, 15.26
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VIII. The Reaction Quotient (Q)
Given the initial concentrations of reactants and products, we can determine the direction the reaction will proceed in.
Substitute concentrations into the reaction quotient expression, which is the same as K except NOT at equilibrium.
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K uses equilibrium concentrations!!!!!!
Q uses initial concentrations!!!!!!
K-Dubs, 6th grade
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If Q>K, then there is an excess of products which will react to form reactants to establish equilibrium (shift left).
If Q<K, then there is an excess of reactants which will react to form products to establish equilibrium (shift right).
If Q=K, equilibrium is established.
Ajobi.net
HW: 15.28
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IX. Calculating Equilibrium Concentrations
Ex 1) At 500 K the value of Kp is 0.497 for the following reaction:PCl5(g) PCl3(g) + Cl2(g)If the partial pressure of PCl5 is 0.860 atm and the partial pressure of PCl3 is 0.350 atm at equilibrium, what is the partial pressure of Cl2 in the mixture?
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Ex 2) Using the equilibrium from Ex. 1, what are the equilibrium partial pressures of all species if PCl5 has an initial pressure of 1.66 atm? Desperatelyseeking
suddenlysusan. wordpress.com
HW: 15.34, 15.36, 15.38, 15.40
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TO BE CONTINUED…
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Equilibrium Part 2
Ch. 15 in Textbook
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X) Le Chatelier’s PrincipleA) Stress
Once an equilibrium is established, the forward and reverse reactions will proceed at equal rates and the amounts of reactants and products will not change.
Equilibrium will continue indefinitely unless conditions are somehow changed to disrupt it.
A disturbance to the equilibrium is called a stress.
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B) The Principle
When you deal with stress in your own life (e.g. taking this class) you do something to rid yourself of the stress and re-establish your personal equilibrium.
Similarly, French industrial chemist Henri-Louis Le Chatelier stated that when a stress is applied to a chemical equilibrium, the equilibrium will shift its position to eliminate the disturbance.
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C) Changes in Concentration
Adding a reactant or a product to an equilibrium mixture causes the equilibrium to speed up in the direction that will remove the excess.
This shift is only temporary and a new equilibrium is established with new equilibrium concentrations (although no change in K).
Chem.ufl.edu
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Similarly, removing a reactant or product from an equilibrium mixture causes the equilibrium to speed up in the direction that will make up for the deficit.
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How can we maximize our ammonia output in the Haber Process?
N2(g) + 3H2(g) ↔ 2NH3(g)
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Link
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D) Changes In Volume/Pressure
The pressure may be increased by reducing the container volume or the addition of a non-reacting gas.
The equilibrium will speed up in the direction that will reduce the pressure through the production of fewer moles of gas.
En.wikibooks.org
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Similarly, the pressure may be decreased by increasing the container volume or the removal of a non-reacting gas.
The equilibrium will speed up in the direction that will increase the pressure through the production of greater moles of gas.
This shift is only temporary and a new equilibrium is established with new equilibrium concentrations (although no change in K).
Iforgottocitethis.com
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How can we maximize our ammonia output in the Haber Process?
N2(g) + 3H2(g) ↔ 2NH3(g)
Cafepress.com
Link
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E) Changes in Temperature
Increasing the temperature results in an excess of heat, causing the equilibrium to speed up in the direction that removes the heat (endothermic).
C-p-p.co.uk
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Similarly, lowering the temperature results in a deficit of heat, causing the equilibrium to speed up in the direction that produces heat (exothermic).
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Unlike all other stresses, however, the temperature changes the value of K.
In other words, a completely different equilibrium mixture is created at the different temperature.
If a reaction shifts to the right, then K increases.
If a reaction shifts to the left, then K decreases.
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How can we maximize our ammonia output in the Haber Process?
N2(g) + 3H2(g) ↔ 2NH3(g) + heat
Wow.comLink
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F) Adding Catalysts A catalyst lowers the
activation energy for both the forward and the reverse reactions.
A catalyst therefore speeds up the forward and reverse reactions equally.
A catalyst speeds up the rate at which equilibrium is achieved, but the equilibrium mixture and K remain exactly the same.
En.wikivisual.com
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Haber found that iron mixed with metal oxides allowed the Haber Process to run at sufficiently low temperatures.
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HW: 15.44, 15.46
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Drumming Chimp Outro