Physical Chemistry 1.1 - Chemical Equilibrium - K and the Ionic Product of Water Flashcards
When is a chemical reaction at equilibrium?
when the concentrations of the reactants and products is unchanging (and the rate of the forward and reverse reactions is equal)
K (the ___ ___) is a ___ of reactants to products.
equilibrium constant, ratio
K characterises the ___ of a reaction ___.
K has no ___.
composition, mixture.
units
For the general reaction:
aA + bB ⇌ cC + dD
What is K?
C^c x D^d
————— = K
A^a x B^b
A, B, C and D represent…
a, b, c and d represent…
the concentrations of the reactants/products at equilibrium.
the mole ratio (or ‘stochiometric coefficients’)
If K is greater than 1, there are more ___ than there are ___, so equilibrium must be on the (left/right).
vice versa
products, reactants, right
Which two things are not included in the expression for K?
> They are given a value of _.
pure solids and liquids.
zero (0)
Solids and liquids do not affect the ___ of ___.
position of equilibrium
If K is very small (<10-3) then there is very little ___ and so (very little / a lot) of the reaction has taken place.
product, a little
If K is very large >10^3, the reaction is effectively ___.
complete
When K = 1, the concentration of the products ___ that of the reactants.
equals
What does K give no indication of?
the rate at which equilibrium was established
What does Le Chatlier’s principle state?
that any change imposed on an equilibrium will cause the equilibrium to shift in the direction that minimises the effects of that change
What is K unaffected by?
What is K affected by?
unaffected by:
increasing/decreasing concentrations, changes in pressure, catalysts
affected by: temperature
How does a rise in temperature affect K…
1. In endothermic reactions?
2. In exothermic reactions?
K will increase, as the product yield increases (K = P/R).
K will decrease, as the product yield decreases
Catalysts (do/do not) affect the value of K.
do not
The ICE box method allows us to find the value of __ when we’re given certain concentrations of ___ and/or ___ in an equilibrium reaction.
What does ICE stand for?
K, reactants, products.
Initial (concentration)
Change (in concentration)
Equilibrium (concentration)
You will be given the concentrations of some of the species and asked to find K.
To calculate K, you will need…
……2(SO2) + O2 ⇌ 2(SO3)
I……..1…………0.7………..0
C…….?…………..?…………..?
E…….?…………..?………….0.8
What is the value of each of the question marks?
the concentrations of reactants and products at Equilibrium.
……2(SO2) + O2 ⇌ 2(SO3)
I……..1…………0.7………..0
C…..-0.8…….-0.4………+0.8
E…….0.2……..0.3……….0.8
Using the data on the previous card, calculate K.
K = (0.8)^2 / (0.2)^2 x (0.3)
K = 4.8
*You can tell by looking at the equilibrium concentrations that K will be >1.
What is the equilibrium of water?
OH2 (l) ⇌ OH- (aq) + H+ (aq)
OR
OH2 (l) + OH2 (l) ⇌ OH- (l) + OH3+ (this one more advanced highery)
How is water pH neutral?
because it dissociates into OH- and H+ in equal concentrations
Answer these questions about the H3O+ ion.
1. What is it called?
2. What can it be referred to as?
3. What else can it be written as?
- a hydronium ion
- a hydrated proton
- H+
In water and aqueous solutions there is an equilibrium between the water molecules, and ___ and ___ ions.
hydronium and hydroxide ions.
The ionic product of water is an important equation that looks like:
Kw = [H+] x [OH-]
The ionic product of water (Kw) is an ___ ___ for water.
What does this look like?
equilibrium constant.
Kw = [OH-]^1 (g) x [H+]^1 (g) / [OH2]^2 (l)
↑this is for understanding only (water is a liquid and so should not be included)
In pure water, and solutions with pH 7, what does Kw equal?
What do [H+] and [OH-] equal in pure water?
1x10^-14
Both 1x10^-7
This tells us that equilibrium is (slightly/far) to the (reactants/products) side.
far, reactants side (the water)
In solutions other than pure water, the equation Kw = [H+] x [OH-] can be used to find the pH by…
rearranging for [H+], if you know [OH-]
If the concentration of OH3+ or OH- is known, the concentration of the other ion can be calculated using which two equations?
Kw (OHxH=1x10^-14), or
pH + pOH = 14 (which is just the -log of Kw)
Both in data booklet
Kw is dependent on ___.
temperature (just like all equilibrium constants)
Kw only equals 1x10^-14 at ___.
25 degrees celsius/298 kelvin
Kw increases as ___ increases.
temperature
The relationship between pH and hydrogen ion concentration is given by…
pH = - log(H+) and H+ = 10^-pH
‘p’ basically just means ‘___’
-log
