Physical Chemistry 1.1 - Chemical Equilibrium - K and the Ionic Product of Water

Question 1

When is a chemical reaction at equilibrium?

Answer 1

when the concentrations of the reactants and products is unchanging (and the rate of the forward and reverse reactions is equal)

Question 2

K (the ___ ___) is a ___ of reactants to products.

Answer 2

equilibrium constant, ratio

Question 3

K characterises the ___ of a reaction ___.
K has no ___.

Answer 3

composition, mixture.
units

Question 4

For the general reaction:
aA + bB ⇌ cC + dD
What is K?

Answer 4

C^c x D^d
————— = K
A^a x B^b

Question 5

A, B, C and D represent…
a, b, c and d represent…

Answer 5

the concentrations of the reactants/products at equilibrium.
the mole ratio (or ‘stochiometric coefficients’)

Question 6

If K is greater than 1, there are more ___ than there are ___, so equilibrium must be on the (left/right).
vice versa

Answer 6

products, reactants, right

Question 7

Which two things are not included in the expression for K?
> They are given a value of _.

Answer 7

pure solids and liquids.
zero (0)

Question 8

Solids and liquids do not affect the ___ of ___.

Answer 8

position of equilibrium

Question 9

If K is very small (<10-3) then there is very little ___ and so (very little / a lot) of the reaction has taken place.

Answer 9

product, a little

Question 10

If K is very large >10^3, the reaction is effectively ___.

Answer 10

complete

Question 11

When K = 1, the concentration of the products ___ that of the reactants.

Answer 11

equals

Question 12

What does K give no indication of?

Answer 12

the rate at which equilibrium was established

Question 13

What does Le Chatlier’s principle state?

Answer 13

that any change imposed on an equilibrium will cause the equilibrium to shift in the direction that minimises the effects of that change

Question 14

What is K unaffected by?

What is K affected by?

Answer 14

unaffected by:
increasing/decreasing concentrations, changes in pressure, catalysts

affected by: temperature

Question 15

How does a rise in temperature affect K…
1. In endothermic reactions?
2. In exothermic reactions?

Answer 15

K will increase, as the product yield increases (K = P/R).
K will decrease, as the product yield decreases

Question 16

Catalysts (do/do not) affect the value of K.

Answer 16

do not

Question 17

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?

Answer 17

K, reactants, products.
Initial (concentration)
Change (in concentration)
Equilibrium (concentration)

Question 18

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?

Answer 18

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

Question 19

Using the data on the previous card, calculate K.

Answer 19

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.

Question 20

What is the equilibrium of water?

Answer 20

OH2 (l) ⇌ OH- (aq) + H+ (aq)
OR
OH2 (l) + OH2 (l) ⇌ OH- (l) + OH3+ (this one more advanced highery)

Question 21

How is water pH neutral?

Answer 21

because it dissociates into OH- and H+ in equal concentrations

Question 22

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?

Answer 22

1. a hydronium ion
2. a hydrated proton
3. H+

Question 23

In water and aqueous solutions there is an equilibrium between the water molecules, and ___ and ___ ions.

Answer 23

hydronium and hydroxide ions.

Question 24

The ionic product of water is an important equation that looks like:

Answer 24

Kw = [H+] x [OH-]

Question 25

The ionic product of water (Kw) is an ___ ___ for water.

What does this look like?

Answer 25

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)

Question 26

In pure water, and solutions with pH 7, what does Kw equal?
What do [H+] and [OH-] equal in pure water?

Answer 26

1x10^-14
Both 1x10^-7

Question 27

This tells us that equilibrium is (slightly/far) to the (reactants/products) side.

Answer 27

far, reactants side (the water)

Question 28

In solutions other than pure water, the equation Kw = [H+] x [OH-] can be used to find the pH by…

Answer 28

rearranging for [H+], if you know [OH-]

Question 29

If the concentration of OH3+ or OH- is known, the concentration of the other ion can be calculated using which two equations?

Answer 29

Kw (OHxH=1x10^-14), or
pH + pOH = 14 (which is just the -log of Kw)
Both in data booklet

Question 30

Kw is dependent on ___.

Answer 30

temperature (just like all equilibrium constants)

Question 31

Kw only equals 1x10^-14 at ___.

Answer 31

25 degrees celsius/298 kelvin

Question 32

Kw increases as ___ increases.

Answer 32

temperature

Question 33

The relationship between pH and hydrogen ion concentration is given by…

Answer 33

pH = - log(H+) and H+ = 10^-pH

Question 34

‘p’ basically just means ‘___’

Answer 34

-log