Chemistry Unit Test On Equilibrium Constant And Entropy

Front 1

When is a reaction one way?

Back 1

It is unlikely 3 products will combine again. So when it is unlikely so many products will combine again.

Front 2

dynamic equilibrium

Back 2

reversible rxns in a closed system. The rate of the fwd rxn = rate of reverse rxn

Front 3

How can you tell when equilibrium is reached?

Back 3

All macroscopic properties (vol, temp, press) are constant

Front 4

Three types of equilibrium systems

Back 4

Phase Equilibrium
Solubility EqM
Chemical

Front 5

Phase Eqm

Back 5

Two or more states of a pure substance are in eqm. H2O(l) <=> H2O(g)
Rate evaporation=rate condensation
For every molecule that evaporates, one condenses

Front 6

Solubility Eqm

Back 6

Solute in a saturated solution of a solvent. Rate dissolving = rate crystallyzation.
CuSO4(s) <=>Cu2+(aq) + SO42-(aq) Solid solute in eqm with its ions

Front 7

solute

Back 7

the dissolved matter in a solution; the component of a solution that changes its state

Front 8

solvent

Back 8

a liquid substance capable of dissolving other substances; "the solvent does not change its state in forming a solution"

Front 9

saturated

Back 9

being the most concentrated solution possible at a given temperature; unable to dissolve still more of a substance; "a saturated solution"

Front 10

Solubility eqm example

Back 10

When I2 solid dissolved, I2 aq come out with little I2 solid at bottom. If you add I2 solid radioactive, and filter, after several hours radioactivity can b detected in solution. "For every iodine in solution, one comes out"

Front 11

Chemical eqm

Back 11

H2(g) + I2(g) <=> 2HI(g)
colourlesspurple colourless
It will b lite purple in closed container.

Front 12

Le Chatelier's Principle

Back 12

When a stress is added to a system at eqm, the system readjusts so as to relieve or offset the stress

Front 13

Haber Process 4 formation of ammonia

Back 13

N2(g) + 3H2(g) <=> 2NH3(g) + 92.5 KJ

Front 14

Draw rate vs time graph 4 chem eqm

Back 14

.

Front 15

Draw conc vs time graph 4 chem eqm

Back 15

.

Front 16

Adding a catalyst...

Back 16

decreases activation energy for the fwd and rev rxns by the same amount so that the fwd and reverse rxn both increase by the same amount. This has no effect on eqm except that this state is established faster

Front 17

When something is added in eqm to react with a reactant....

Back 17

the concentration of this reactant decreases

Front 18

Review limiting reactants

Back 18

.

Front 19

Keq = what ks?

Back 19

Kfwd / Krev

Front 20

k >> 1

Back 20

large value.
goes to completion
[PRODUCTS] / [reactants]

Front 21

k << 1

Back 21

Little rxn at all
[products] / [REACTANTS]

Front 22

k ~ 1

Back 22

intermediate value
Measurable amounts of product and reactant at eqm

Front 23

Pure solids or liquids

Back 23

have constant []'s so are omitted from Keq calc

Front 24

The only things that affect Kc

Back 24

temp and pressure

Front 25

To convert from conc to mol

Back 25

multiply by number of Litres

Front 26

For (1-2x) simplifying assumption to check % is:

Back 26

2x / 1

Front 27

For (2-3x) simplifying assumption to check % is:

Back 27

3x / 2

Front 28

if Q>K

Back 28

shifts left

Front 29

if Q=K

Back 29

at eqm

Front 30

If Q<K

Back 30

shift rite

Front 31

At constant temp, [] is directly related to the

Back 31

partial pressure of the gas

Front 32

[] of gases can b expressed in terms of

Back 32

partial pressures

Front 33

P=

Back 33

(n/v)RT

Front 34

Partila pressure formula =

Back 34

(n / v) RT = []RT

Front 35

R in pressure formulas =

Back 35

.0821 atm *L / mol*K

Front 36

Kp =

Back 36

Kc (RT)^dn

Front 37

Kc = Kp only when

Back 37

same # moles on each side

Front 38

When excess solid is present in a saturated solution...

Back 38

there is a SOLUBILITY EQM formed between the solid and its ions

Front 39

solubility constant is

Back 39

Ksp = equilibrium product constant = ion product constant

Front 40

Ksp is dependent on

Back 40

temp. not pressure bcs not gas

Front 41

Ksp only written for

Back 41

ionic compounds w/low solubility

Front 42

If solubility is high....

Back 42

ionic compound dissolves completely

Front 43

Concentration X # litres = new

Back 43

concentration! ex; [Ag+]

Front 44

precipitate

Back 44

Precipitation is the formation of a solid in a solution during a chemical reaction. When the reaction occurs, the solid formed is called the precipitate, and the liquid remaining above the solid is called the supernate.

Front 45

The precipitate will precipitate until

Back 45

Qsp = Ksp

Front 46

100 rule

Back 46

assumption valid as long as [ion] is 100x > Ksp

Front 47

reread "effect of a common ion on solubility"

Back 47

.

Front 48

entropy is

Back 48

a measure of molecular randomness or disorder

Front 49

nature spontaneously proceeds towards...

Back 49

the states that have the highest probability of existing.
Probability favours a disordered state

Front 50

Positional entropy

Back 50

Entropy increases if the # of configurations in space (positional microstate) increase. That is, more possible positions.

Front 51

1st law of thermodynamic

Back 51

Energy is never created/destroyed. Energy of universe is constant

Front 52

2nd law of thermodynamic

Back 52

Spontaneous processes will increase the entropy of the universe. The entropy of the universe is increasing.
dSuniv = dSsyst + dSsurr

Front 53

If dSuniv>0

Back 53

rxn is spontaneous

Front 54

if dSuniv <0

Back 54

rxn spontaneous in opp direction

Front 55

if dSuniv=0

Back 55

equilibrium

Front 56

Exothermic systems increase molecular motions in the surroundings so

Back 56

dSsurr = +
and dH = -

Front 57

For endothermic

Back 57

dH = +
and dSsurr = -

Front 58

if dSsys > 0

Back 58

spontaneous fwd

Front 59

If dSsurr < 0

Back 59

spontaneous rev

Front 60

What actually occurs (fwd or rev) depends on

Back 60

temp

Front 61

The impact of a transfer of energy as heat to the surroundings will be greater at

Back 61

lower temps (a greater % change in randomness)

Front 62

dSsurr =

Back 62

-dH / T (J/K) At constant temp and pressure. Point of view of surroundings are opp to system

Front 63

Gibb's Free Energy deals with

Back 63

the temp factor.
dG = dH - TdS All quantities refer to system.

Front 64

dSuniv = -

Back 64

-dG / T

Front 65

Rxns at constant temp and pressure will b spontaneous only if

Back 65

dG is neg

Front 66

Spontaneity requires that free energy must

Back 66

decrease

Front 67

3rd Law of Thermodynamics:

Back 67

The entropy of a perfect crystal is zero at absolute zero.Theoretical. Every substance has a measurable absolute entropy.

Front 68

dS*rxn =

Back 68

sigma np S*p - sigma nr S*r

Front 69

No instrument can measure

Back 69

free energy

Front 70

three methods of calcing dG*: 1

Back 70

dG* = dH* - TdS*

Front 71

three methods of calcing dG*: 2

Back 71

dG is a state function (indep of pathway). thrfr we can determine using a procedure similar to Hess's Law and dH

Front 72

Standard Free Energy of Formation Method 3

Back 72

dG* = sigma np dG*f(prod) -- sigma nr dG*f(reactats)
at 25 C and 1 atm

Front 73

To calc dG not at STP use

Back 73

dG = dG* + RT lnQ
in J and K and stuff where K=8.314

Front 74

The lowest possible free energy that chemical systems always seek occurs at eqm where

Back 74

dG = 0
Q = K (Kp or Kc)

Front 75

Therfore, rearranging olden equaiton with zeros and Qs....

Back 75

dG* = -RT lnK

Front 76

When Q = K, free energy is

Back 76

at a min

Front 77

Is it the sign of dG or dG* that determines the direction of the rxn's spontaneity?

Back 77

dG

Front 78

What does dG* tell us?

Back 78

The relative amounts of products and reactants when eqm is reached.

Front 79

If K>1, ln K, dG* and comments

Back 79

ln K = +
dG* = -
Comments = products favored over reactants at eqm

Front 80

If K=1, ln K, dG* and comments

Back 80

ln K = 0
dG* = 0
Comments = products and reactants equally favored at eqm

Front 81

If K<1, ln K, dG* and comments

Back 81

ln K = -
dG* = +
Comments = reactants favored over products and eqm

Front 82

neg dH favours

Back 82

fwd

Front 83

neg dS favours
(of sys)

Back 83

rev

Front 84

When pressure is lower

Back 84

vol is bigger. So lowering pressure increases entropy.

Front 85

dG and dH units

Back 85

kJ / mol

Front 86

dS units are

Back 86

J / K mol

Front 87

propane

Back 87

C3H8(g)