AP Chemistry Unit 7 Review: Equilibrium!
TLDRThe video script discusses the concept of chemical equilibrium, emphasizing the equilibrium constant as a critical factor in understanding how reactions balance themselves. It explains the relationship between reactants and products, and how to calculate the equilibrium constant based on their concentrations or pressures. The script also delves into how changes in conditions such as temperature, reactant amounts, and container size can shift equilibrium. Furthermore, it clarifies the difference between KP and KC, and concludes with an explanation of rate laws, focusing on the rate-determining step and how to derive the overall rate law for a reaction.
Takeaways
- π Chemical equilibrium refers to the state where reactions balance themselves without indicating the speed of balancing.
- π The equilibrium constant (K) is crucial for understanding chemical equilibrium; it's the ratio of products to reactants.
- π At equilibrium, forward and backward reactions occur simultaneously, with their rates being equal.
- π When calculating the equilibrium constant, ignore solids and liquids, focusing only on gases and solutions.
- π’ The equilibrium constant expression is built using the concentrations of products raised to their stoichiometric coefficients and placed over reactants' concentrations.
- π For Kc (concentration constant), use concentrations, and for Kp (pressure constant), use pressures instead.
- π‘ The equilibrium constant K value indicates how favored the products are over the reactants; a large K means more product concentration is favored.
- π The reaction quotient (Q) is used to determine the direction a reaction will proceed in; compare Q to K to know if the reaction will favor products or reactants.
- βοΈ Le Chatelier's principle states that a system will adjust to counteract changes made to it, such as adding reactants or increasing temperature.
- π Rate laws are determined by identifying the rate-determining step (the slowest step) and using it to express the overall rate of the reaction.
Q & A
What is the main topic of the video?
-The main topic of the video is chemical equilibrium, specifically focusing on how chemical reactions balance themselves.
What does the term 'equilibrium' mean in the context of chemistry?
-In chemistry, 'equilibrium' refers to a state where the forward and backward reactions occur at the same rate, resulting in a balance without any net change in the concentrations of reactants and products.
What is the equilibrium constant and why is it important?
-The equilibrium constant, denoted as K, is the ratio of the concentration of products to the concentration of reactants raised to the power of their respective stoichiometric coefficients. It is important because it provides a measure of the extent to which a reaction favors the formation of products over reactants at a given temperature.
How does one calculate the equilibrium constant for a given reaction?
-To calculate the equilibrium constant, K, one must express it as the product of the concentrations of the products raised to the power of their stoichiometric coefficients in the balanced chemical equation, divided by the product of the concentrations of the reactants raised to the same powers.
What is the significance of the equilibrium constant value in predicting the direction of a reaction?
-A large K value indicates that the reaction favors the formation of products, while a small K value suggests that the reaction favors the formation of reactants. If the reaction quotient (Q) is greater than K, the reaction will shift towards the reactants, and if Q is less than K, the reaction will shift towards the products.
What are the different types of equilibrium constants and how do they differ?
-Different types of equilibrium constants include K, Kp, Ka, Kb, and Kw. They differ based on the units used for their expressions, with K typically using concentration units (M), Kp using pressure units (atm), and Ka, Kb, and Kw being specific to acid dissociation, base dissociation, and water dissociation, respectively.
How does changing the concentration of a reactant affect the position of equilibrium?
-Increasing the concentration of a reactant will shift the equilibrium towards the products to counteract the change, according to Le Chatelier's principle. This is because the system tries to reduce the concentration of the added reactant by forming more products.
What happens when the temperature is increased for an exothermic reaction?
-For an exothermic reaction, increasing the temperature will cause the equilibrium to shift in the direction that absorbs heat, which is towards the reactants. This is because the system tries to reduce the added heat by favoring the endothermic process (formation of reactants).
How does the size of the container affect the equilibrium of a reaction involving gases?
-Changing the size of the container affects the equilibrium of reactions involving gases by altering the number of gas molecules on each side of the reaction. If the container size is reduced, the reaction will shift towards the side with fewer gas molecules to reduce the pressure increase caused by the smaller volume.
What is the rate-determining step in a chemical reaction?
-The rate-determining step is the slowest step in a chemical reaction mechanism. It determines the overall rate of the reaction because the faster steps will adjust to match the rate of the slowest step, causing a 'traffic jam' at this step.
How can one determine the overall rate law of a reaction?
-To determine the overall rate law, one must first identify the rate-determining step. Then, using the stoichiometric coefficients from this step, an expression for the rate law can be written. This expression is then modified using equilibrium expressions to eliminate any intermediates that are not present in the reactants or products.
Outlines
π Introduction to Chemical Equilibrium
The paragraph introduces the concept of chemical equilibrium, explaining it as a balance between reactants and products in a chemical reaction without indicating the speed of the reaction. It emphasizes the importance of the equilibrium constant (K), which is the ratio of the concentration of products to the concentration of reactants. The explanation includes an example of the Haber-Bosch process for synthesizing ammonia and clarifies that the equilibrium constant is independent of the reaction speed. The paragraph also discusses how to calculate the equilibrium constant and the significance of the equilibrium constant in determining the favorability of products over reactants.
π Understanding the Equilibrium Constant (K)
This paragraph delves deeper into the equilibrium constant (K), explaining how it can be used to predict the direction in which a reaction will proceed. It introduces the concept of the reaction quotient (Q), which is used to compare the current state of a reaction to the equilibrium state. The discussion includes how changes in concentration, temperature, and pressure can shift the equilibrium position. The paragraph also briefly touches on the differences between KP (related to pressure) and KC (related to concentration), and the implications of these differences. Lastly, it provides a brief overview of how changes in the system, such as increasing a reactant or decreasing container size, can affect the direction of the reaction.
π§ͺ Determining Rate Laws and Reaction Mechanisms
The final paragraph focuses on the process of determining rate laws for chemical reactions. It explains that the rate of the overall reaction is determined by the slowest step, known as the rate-determining step. The paragraph outlines the method for identifying this step and using it to derive the overall rate law. It also discusses how equilibrium expressions can be used to eliminate intermediates from the rate law equation. The explanation includes an example of how to derive a rate law by considering the slow step and the equilibrium expression, ultimately showing how to arrive at a simplified rate law expression.
Mindmap
Keywords
π‘Chemical Equilibrium
π‘Equilibrium Constant (K)
π‘Rate Laws
π‘Le Chatelier's Principle
π‘Stoichiometric Coefficients
π‘Reactants and Products
π‘Dynamic Balance
π‘Concentration
π‘Pressure
π‘Temperature
π‘Gas Molecules
Highlights
Introduction to chemical equilibrium and its significance in balancing chemical reactions.
Explanation of the equilibrium constant, its role as the ratio of products to reactants, and its importance in understanding chemical balance.
Discussion on how the equilibrium constant cannot provide information about the speed of reactions, but only the point of balance.
Clarification on the difference between various types of equilibrium constants such as K, Kb, Kp, and Kw, and their relevance to specific scenarios.
Explanation of how to calculate the equilibrium constant (K) for a given reaction, using the example of the Haber-Bosch process.
Importance of considering the physical state of reactants and products when calculating equilibrium constants, with the exclusion of solids and liquids.
Illustration of how the equilibrium constant (K) value indicates the favorability of products over reactants, and its implications for reaction direction.
Use of the reaction quotient (Q) to determine the direction a reaction will proceed from a non-equilibrium state, and comparison of Q with K.
Explanation of how changes in system conditions like concentration, temperature, and pressure can affect the direction of a chemical reaction.
Discussion on the difference between KP (involving pressure) and KC (involving concentration), and the relationship between them.
Overview of Le Chatelier's principle and its application to predict how a system will respond to changes in reactants, temperature, and container size.
Introduction to rate laws and the concept of the rate-determining step in chemical reactions.
Methodology for determining the overall rate law of a reaction by focusing on the slow step and utilizing equilibrium expressions.
Explanation of how to manipulate and simplify rate laws using equilibrium expressions to eliminate intermediate species.
Final thoughts on the importance of understanding rate laws for predicting reaction outcomes and the practical applications of this knowledge.
Transcripts
all right if your boy kirara with
another camp crash course all right I
draw anything out of context probably
think I really cringe but I'm actually
not okay
oh hi I'm moving on moving on okay hello
everybody I'm Cara and today we are
going to be talking about chemical
equilibrium if you weren't able to read
that but you probably couldn't how I
wrote it but we're going to be talking
about how chemical reactions
balance themselves so that's what
equilibria mean now because it means
balance it doesn't tell you anything
about the speed at which it balances it
just says where it balances that's all
the chemical equilibrium can't tell you
so do not try to figure out how fast the
reaction is happening by using anything
we talked about in this video except at
the end we'll have a little compute on
that so now the most important thing to
understand about equilibrium is the
equilibrium constant because once you
understand equilibrium constant
everything else falls into place
basically the equilibrium constant is
the ratio of your product to reactor so
let us say beyond the reaction and 2 + 3
H to yield to nh3 this basically the
haber-bosch model oops I forgot my
backward error don't forget in
equilibrium your lies have forward and
backward reactions happening at the same
time and the definition of equilibrium
the one though they're equal so let's
say we wanted to find the equilibrium
constant of the reaction symbolize K now
what I'm finding the equilibrium
constant I don't care Oh like it doesn't
even cross my mind whether it's k KS p k
a.kb
KW i don't care just keep to yourself ok
I'm good we don't care the only thing I
care about in the reaction and the phase
is a matter of the reaction reactants
and products so let's write it all you
guys thankfully are gases so when you're
finding the equilibrium constant you
basically go with the product first and
you say it needs to be the first product
and we basically symbolize it with
concentration of nh3
you guys are concentration or you can do
pressure and then you take this
coefficient that's in front of it and
you put it to the power of that so we do
n HP squared and then in the denominator
we gotta do the reactants so we first
got n2 which does not have a which has a
coefficient of 1 so we don't put a power
and then we have h2 which is coated in 3
they put it a third power okay so this
is our equilibrium expression now yet be
careful because in this case we got
lucky and they're all gases but whenever
you're calculating an equilibrium
content you have to ignore solids and
liquids the only thing that matter
gases and equally a solution so you
might be asking Kirara why don't you
care whether it's K or K B or k XP or
whatever nonsense the reason in the
clause if you only care about the baby
that matter it eventually give you the
right equilibrium constant regard for
example KSP right let's see so let's say
you AG CL yields in d plus plus CL minus
and it wanted us to find the KSP of it
you might have to pay that matter we say
this solid cuz it's a solid that you
want to dissolve and then it goes into a
pH solution wants it dissolved so if we
use the same strategy meeting before we
use the products of AG plus no
covariance to deal with here co-
we don't have to put in this because of
solvent and we didn't even think about
it but we did get the KSP properly the
only thing you have to know it's a
really uh reaction and the bigger the
matter and you automatically get
everything let's do a KB and K a thing
so for K a we could say h2so4 + h2o eh -
bo + + hso4 month and basically we know
that this is aqueous this is liquid this
is aqueous and this also and then we
know that there's a k-8 because we're
dealing with an acid associating and we
don't even out worry about swaggins K
and we gonna write the equilibrium as we
always did interview a + time hso4 minus
/ h2so4 and meeting in the think about
what it means to have a k-8 we just
found the equilibrium constant for the
reaction and we are coochi game 2169 i
don't care
okay so what the heck does the k value
actually tell it tells us how much the
products are favored over the reactants
right but you're putting concentration
of products over upon the occasion of
reaction so if your K is really big that
means that you want to have a lot more
concentration of products if KT has
really small does anyone have less
products and a lot of reactants what
this should be equilibrium but anyway
another thing we can do with equilibrium
is tell us which way the reaction is
going to go from our given position so
equilibrium constant is why new system
of the equilibrium what that ratio of
equal to what your system is not always
at equilibrium right let's go back to
our Hebrew box example so let us say
that we had like 0.1 atmosphere of 83
and 0.2 atmosphere of h2 and then 0.05
atmosphere
and two I just made these numbers up so
there's no way that this is already at
equilibrium so how do we know which way
it's gonna go is it gonna make you more
three years are gonna make more NH 2
what's X at each ear and who or H 2 all
we know that by doing cute and the way
you find cute is exactly the same as
finding K except this app it's current
time what is that ratio of equal to
right now even though it might not be at
equilibrium so well calculated 0.1
squared / 0.2 times 0.05 and then this
have to be cute and basically if this Q
value is greater than our K then we know
that there's too many products because
the numerator is way bigger than the
denominator and we don't want that so
that means that the reaction is gonna
keep going left it's gonna produce more
and do an h2 because it's not yet that
you Calibri amande want to get rid of
the product it's the other way around
with it less than k then i'll go the
other way okay so that's how you use
cute cue that any instant in time cave
what it wants to be at equilibrium
all right let's quickly go over what KP
with KC is because these are the only
two that are actually different from
each other
so KP the P stands for pressure and it's
basically when you use pressures instead
of concentration because you can do that
with kids and then Casey what do you
expect
you can concentration now the way I like
to remember the difference between these
two is because like your a pressure
times volume and people to NRT by the
ideal gas on right so your n over B
which is equal to your concentration is
going to be equal to P over RT so let's
say the KP is equal to PA times PB over
PC right this corresponds to the
reaction C goes to a plus B and they
know what gas is coming out of pressure
I mean then we also know that the
canacee are going to be concentration of
a kind of concentration of B over
concentrated on steep so if we plug in
this equation for over here we get RT
squared did not fit in the numerators
denominator and then we get an RT the
first power and the denominator
denominator and we're left with the KC
is equal to PA times PB over RT PC so
basically all I'm trying to show you is
that KP and K C are very different and
if you want to see how two different
just take this equation that I showed
you and plug it in to the corresponding
concentration equation and you should be
good but anyway this like pretty
I don't think it's gonna be on the exam
I'm not sure our teacher taught us but
she mentioned it very briefly so I don't
think it would be that useful okay
okay two more things in the shack and
finding rate laws okay so the shack it
basically said that your system is gonna
contract any change in it but basically
they're like four ways in which the work
to go to haber-bosch again and here Bob
does pretty end up there make I'm pretty
sure let me just purify this wow I'm
very good at it extra EXO's exothermic I
can speak to Exeter okay so the fourth
thing that can happen is first you
increase one of the reactants so let's
NAT says it wants to undo that so how's
it gonna do that it's gonna take this
reaction towards the right because if
you increase of reactants you know I can
get rid of them you have to turn them
into more product so we'll draw an arrow
that says their equilibrium is shifting
right - in peace product exactly the
same except opposite logic okay increase
temperature the way I like to think
about this is like if going forward in
the reaction releases heat right
exotherm then if you increase the 10 you
want to get rid of heat right you don't
want to make more so instead of going
right which made more tea it'll actually
go left okay I probably computing you
more because it's my left not your
litter you guys I left and then the last
thing is reducing size of the container
now this only applies with things with
gases in them and you basically compare
the right side number of gas molecules
on the left side number of gas molecules
so every dude is the container size
right each molecule of gas takes up
certain amount of space so if you want
to counteract the change over getting a
smaller container you also want to
reduce the size of the gas molecule and
in order to do that you just want to
reduce the number of gas molecules
overall so if you reduce the container
size you want to move to the side that
has less gas molecules and in this case
that's the right so your reaction gonna
move right ok very epic battle a champ
let's talk about the last important
thing determining rate laws all right
he's getting it every problem I found
off the internet and it basically gives
you a bunch of rate laws and I want you
to find the overall rate law of the
reaction so my favorite way to approach
this problem and just a right
many acquainted as you can of course the
first thing I don't recognize it wants
the rate-determining step that's right
the slow step because everything gonna
get traffic jammed at the slow step
because that guy is hanging long this is
like if you're running in line right the
fast guy they're gonna run but then the
guys behind the slowlier is gonna get
stuck with your water I don't know how
is analogies going but he gets ideas the
slow step is the rate determining step
it's the front guy is slow everybody
below behind it was gonna be slow so
essentially it's the rate of the overall
reaction is that the rate of the slow
step and when you're given elementary
stuff you're allowed to you the
coefficient to determine the rate law so
in this case the rate law right now is
kate no.2 no.3 however our actual
reaction doesn't have any no.3 in it so
like this rate law doesn't really make
much sense because we shouldn't have to
know about intermediates in order to
determine the rate law of an overall
reaction so we somehow to get rid of
this no.3
so where can we write equated well we
can't write any equation for kinetics
the Koch kinetics is purely expressions
you can't write any equation so what do
we have to write equation for that's
right equilibrium that's why your time
but you can leave me today get it ha ha
no I don't know what I'm saying so
basically if we write the equilibrium
expression basically you know the
forward rate is equal to the backward so
k1 and 205 is equal to K negative 1 no.2
and no.3 now all I have to do is just
ignore all the case ok we don't care
about cave because eventually they'll
all just like be they'll be some random
like k 1 over k 1 negative 1 over K
times K times there's another key 3
times k2 but we don't care because that
all could just be written out of a
single k we could say that this new KK
prime that we made up is equal to all
the other case so if we can just ignore
them so we have no.2 no.3 here we have n
2 O 5 here and we want to get rid of the
no.3 but we could literally just plug in
the n2o5 for no.2 times and the 3 and we
get that our rate lock is equal to into
a 5 but don't forget we have to put back
or case so let's put our k and boot we
got a rate lon let's say for example
that this over here with the 2 right
then this over here would be n of 2
squared + 2 a 5 squared and then this
over here would be into a 5 squared as
well so that is how you do rate lon you
first
look at the slow stuff and set its rate
to the overall rate okay so you got that
then you look at the equilibrium step
and you're riding the quake and then
once you get to equation you want to see
what's in the reactant side and you want
to get rid of anything that's not on the
reactant side but you can substitution
eliminate whatever it's added do you
want and you only have two things to
worry about your expression that you got
from the rate determining step and your
equilibrium equation alright very happy
that's all I got to talk about if you
got one more of these transporters just
let me know as always if you enjoyed the
video leave a like and subscribe for
more hope it was helpful thing up for
watching again see you guys the next
time
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