Unit 7: Reversible reactions and equilibrium + calculating equilibrium constant Flashcards
When did scientists discover reversible reactions
1803
What does it mean for a reaction to be a reversible reaction
The forward reaction and the backward reaction are occurring at the same rate
What does equilibrium mean
to be in a state of balance
What type of reactions are reversible
insoluble, weak acids, weak bases
when does chemical equilibrium occur
when the opposing reactions equal the same rate
after equilibrium is reached has the reaction stopped?
No, the reaction has not stopped things are still happening but at the molecular level
what reactions are soluble
strong acids, bases and soulble salts
what is the Haber Process
nitrogen gas and hydrogen gas react to produce ammonia
how do you measure the progress of a reversible reaction
reaction quotient or Qc
when can Qc be calculated?
at any point of the reaction because it is not constant
what is the equation for the quotient reaction?
[products] / [reactants]
what is the reaction quotient now called when equilibrium has been reached?
called the equilibrium constant or Kc
Is Kc constant?
Yes Kc is constant
what does Kc tell us
product to reaction concentrations once equilibrium has been reached
What is Qc dependent on?
The progress of the reaction, that is why it can change over time
What happens when Qc has stabilized
equilibrium has been reached
Kc =
Qc
when can equilibrium occur in a reaction?
it can occur at any point of the reaction, and it is unique to that specific reaction
what does equilibrium NOT mean
that the concentrations are the same
what does it mean if K>1
the equilibrium favors products
what does it mean if K<1
the equilibrium favors reactants
what is the equation for the for the inverse of a Kc reaction
1/ Kc
On a particle diagram, when can you tell that equilibrium has been reached
the mlcls are still but changing, but the ratio is consistent
on a haber process graph, how do you know when reactants are favored
when the reactants are less than the products, and vice versa for the products
what should you do when q is smaller than k
when q is smaller than k, then we need to increase the amount of products, and decrease the amount of reactants to increase Q
what should you do when q>k
when q is bigger than k, we need to decrease the amount of products and increase the amount of reactants
why can’t solids and liquids be included in an equlibibrium expression
they do not have concentrations
which states are included in the equilibrium expression
aqueous and gases
what changes the Kc value
temperature
what should you do if you have a reverse reaction when trying to calculate equilibrium constant
take the inverse of the OG Kc
what happens when you multiply a reaction by a factor?
raise the OG Kc to the power of that factor
what should you look @ when trying to calculate the Kc value
always look at the first reaction
what happens when you combine reactions
multiply the Kc constants
what do you use to calculate equilibrium expressions
a rice table
what do you do when an initial concentration or pressure is not given
assume it starts at zero
what ratio will the changes occur in?
mole to mole
what should you do if you don’t know the change or final concentration
use x
How can you use Qc in calculating equil. express.
Qc can be used to see the way the reaction is going to shift, and compare with Kc
