Intermolecular Forces in Solution
(Why substances dissolve?)
Solution Formation
There are three types of interactions among particles in solutions:
Heat of solution and solution cycles
Thermochemical Solution Cycle
∆𝑯𝒔𝒐𝒍𝒏 = ∆𝑯𝟏 + ∆𝑯𝟐
∆Hsoln = negative
(H2SO4 in water)
+
∆𝑯𝟑
∆Hsoln = positive
(NH4NO3 in water)
Heat of solution and
solution cycles
Commercial Cold Packs for Treating Injuries.
▪
These packs contain solid NH4NO3 and
water in separate compartments.
▪
Because ΔHsoln for this solution is positive,
so heat is absorbed from surrounding,
producing local temperatures less than
0°C.
Quantitative Ways Expressing Concentration
▪ Concentration is the proportion of a substance in a
mixture
▪ Concentration is most often expressed as the ratio of the
quantity of solute to the quantity of solution.
Units of Concentration
1. Strength (S): (g/L)
No. of grams of the solute that dissolve in one
liter of the solvent.
2. Part Per Million (ppm): (mg/L or µg/mL)
No. of milligrams of the solute that dissolve in
one liter of the solvent.
3. Part Per Billion (ppb): (µg/L or ng/mL)
No. of micrograms of the solute that dissolve
in one liter of the solvent.
4. Mass percent
𝒘
𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆
%
=
𝒙 𝟏𝟎𝟎
𝒘
𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒗𝒆𝒏𝒕
Units of Concentration
5. Molarity (M)
Number of moles of solute per liter of solution
(mol/L).
6. Molality (m)
Number of moles of solute per kilogram of solvent
(mol/kg).
7. Normality (N)
Number of gram equivalent of solute per liter of
solution.
𝑴=
𝑵𝒐. 𝒐𝒇 𝒎𝒐𝒍𝒆𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆
𝑳𝒊𝒕𝒆𝒓𝒔 𝒐𝒇 𝒔𝒐𝒍𝒗𝒆𝒏𝒕
𝑵𝒐. 𝒐𝒇 𝒎𝒐𝒍𝒆𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆
𝒎=
𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒗𝒆𝒏𝒕 (𝒌𝒈)
𝑵=
𝑵𝒐. 𝒐𝒇 𝒈𝒓𝒂𝒎 𝒆𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆
𝑳𝒊𝒕𝒆𝒓𝒔 𝒐𝒇 𝒔𝒐𝒍𝒗𝒆𝒏𝒕
Units of Concentration
8. Mole Fraction (X)
The mole fraction of any component in a solution
is given by the number of moles of the component
divided by the total number of moles making up
the solution (including solvent)
𝑿=
𝑴𝒐𝒍𝒆𝒔 𝒐𝒇 𝒄𝒐𝒎𝒑𝒐𝒏𝒆𝒏𝒕
𝑻𝒐𝒕𝒂𝒍 𝒎𝒐𝒍𝒆𝒔 𝒎𝒂𝒌𝒊𝒏𝒈 𝒖𝒑 𝒕𝒉𝒆 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏
Equivalent weight
It is weight of compound that contains one equivalent of it
How to calculate Equivalent Weight
𝒎𝒐𝒍𝒂𝒓 𝒎𝒂𝒔𝒔 𝒊𝒏 𝒈𝒓𝒂𝒎
𝑬𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 𝒘𝒆𝒊𝒈𝒉𝒕 =
𝒙
1. 𝐹𝑜𝑟 𝑎𝑐𝑖𝑑𝑠: 𝑥 𝑖𝑠 𝑛𝑜. 𝑜𝑓 𝐻 +
2. 𝐹𝑜𝑟 𝑏𝑎𝑠𝑒: 𝑥 𝑖𝑠 𝑛𝑜. 𝑜𝑓 𝑂𝐻 −
3. 𝐹𝑜𝑟 𝑠𝑎𝑙𝑡: 𝑥 𝑖𝑠 𝑡ℎ𝑒 ℎ𝑖𝑔ℎ𝑒𝑠𝑡 𝑣𝑎𝑙𝑒𝑛𝑐𝑒
4. 𝐹𝑜𝑟 𝑜𝑥𝑖𝑑 − 𝑟𝑒𝑑 𝑟𝑒𝑎𝑐𝑡𝑖𝑜𝑛𝑠: 𝑥 𝑖𝑠 𝑡𝑜𝑡𝑎𝑙 𝑛𝑜. 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛𝑠 𝑡𝑟𝑎𝑛𝑠𝑓𝑒𝑟𝑟𝑒𝑑
𝒘𝒆𝒊𝒈𝒕𝒉 𝒊𝒏 𝒈𝒓𝒂𝒎
𝑵𝒐. 𝒐𝒇 𝒈𝒓𝒂𝒎 𝒆𝒒𝒖𝒊𝒗𝒂𝒍𝒆𝒏𝒕 =
𝑬𝒒. 𝒘𝒕.
Problems
4.00 grams of NaOH was dissolved in water and completed to 250 mL find the
concentration of the resulting solution in all concentration terms mentioned before.
Knowing that density of water = 1.00 g/L and atomic weight (H= 1.008 g/mol, O=16.00 and
Na= 22.99 g/mol) .
Problems
Calculate no of moles present in the following solutions:
1. 500 𝑚𝐿 𝑜𝑓 𝑁𝑎2 𝐶𝑂3 𝑖𝑡𝑠 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 3 𝑀.
2. 4.00 𝑙𝑖𝑡𝑒𝑟𝑠 𝑜𝑓 𝐾𝐶𝑙 𝑖𝑡𝑠 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 1𝑔/𝐿.
Calculate no of gram equivalent present in the following solutions:
1. 50 𝑔 𝑜𝑓𝑁𝑎2 𝐶𝑂3 .
2. 50 𝑔 𝐶𝑎(𝑂𝐻)2 .
3. 100 𝑚𝑙 𝑜𝑓 𝑁𝑎𝑂𝐻 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛 𝑖𝑡𝑠 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 0.5 𝑁𝑜𝑟𝑚𝑎𝑙.
Problems
_BaCl2(aq) + _MgSO4(aq)---> _BaSO4(S) +_MgCl2(aq)
1. Balance this equation then calculate how many mL of BaCl2 solution its
concentration 0.200 N is needed to form 0.200 mole of BaSO4?
What is
equilibrium?
o
Basically, the term refers to what we might call a
"balance of forces“
What is equilibrium?
Mechanical equilibrium
An object is in a state of
mechanical
equilibrium
when it is either static
(motionless) or in a state of
unchanging motion.
Thermal equilibrium
When two objects are brought
into contact, heat will flow from
the warmer object to the cooler
one until their temperatures
become identical.
Chemical equilibrium
The composition will
remain unchanged as long
as the system remains
undisturbed
Chemical Equilibrium
o
A chemical reaction is in equilibrium when there is no
tendency for the quantities of reactants and products to
change.
CaCO3(s) + CO2(aq) + H2O(l) → Ca2+(aq) + 2HCO3-(aq) (1)
Ca2+(aq) + 2HCO3-(aq) → CaCO3(s) + CO2(aq) + H2O(l) (2)
o
Reaction (2) is the reverse of reaction (1).
At equilibrium, the two opposing reactions occur at the same rate.
Concentrations of chemical species do not change once equilibrium
is established.
Chemical
Equilibrium
Applies to the extent (or yield) of
a reaction, the concentrations of
reactant and product present
after an unlimited time (end of
the reaction, no further change)
Reaction Quotient and Equilibrium Constant
• At a given temperature, a chemical system reaches a state in which
a particular ratio of reactant and product concentrations has a
constant value.
Law of chemical equilibrium, or the law of mass action.
This ratio of concentration terms is called :
reaction quotient (Q), also known as the mass-action expression)
Reaction Quotient and Equilibrium Constant
Qc is the ratio between reactant and product concentration
raised to their stoichiometric coefficient at any time.
Kc is the ratio between reactant and product concentration
raised to their stoichiometric coefficient at equilibrium.
The Significance of the Magnitude of K
Using Equilibrium Constant
Knowing the value of the equilibrium constant for a chemical reaction lets
us judge:
• The extent of the reaction;
• Predict the direction of the reaction;
• Calculate equilibrium concentrations from initial concentrations.
Q and K
• Thus, we can make the following generalizations
concerning the direction of the reaction:
• If Qc < Kc net reaction goes from left to right
(reactants to products).
• If Qc > Kc net reaction goes from right to left
(products to reactants).
• If Qc = Kc no net reaction occurs.
Acid Dissociation Constant (Special case for equilibrium constant)
Acidity constant, or Acid-ionization constant (Ka)
Acid dissociation constant (Ka)
HCl =1 x 103
CH3COOH =1.75 × 10−5
Reaction Quotient Forms
1. For an Overall Reaction
Reaction Quotient Forms
2. For a Forward and a Reverse Reaction
Reaction Quotient Forms
3. For a Reaction Involving Pure Liquids and Solids
A pure solid or Liquid always has the same “concentration” at a given temperature,
the same number of moles per liter of its volume, just as density of any pure
material (L) (S) is constant and equal 1.
[Cao(s)]= 1 [CaCO3(s)]= 1
Reaction Quotient Forms
4. For a Reaction with Coefficients Multiplied by a Common Factor
N2(g) + 3 H2(g)
2N2(g) + 6 H2(g)
2NH3(g)
4NH3(g)
[NH3]2
K1=
[N2][H2]3
[NH3]4
K2=
[N2]2[H2]6
The Relationship between Kp and Kc
aA + bB  cC + dD
PAV = n A RT
nA
PA =
RT = [A]RT
V
(𝑃𝐶 )𝑐 . (𝑃𝐷 )𝑑 [𝐶]𝑐 (𝑅𝑇)𝑐 . [𝐷]𝑑 (𝑅𝑇)𝑑 [𝐶]𝑐 [𝐷]𝑑
(𝑐+𝑑)−(𝑎+𝑏)
𝐾𝑃 =
=
=
𝑅𝑇
(𝑃𝐴 )𝑎 . (𝑃𝐵 )𝑏 [𝐴]𝑎 (𝑅𝑇)𝑎 . [𝐵]𝑏 (𝑅𝑇)𝑏 [𝐴]𝑎 [𝐵]𝑏
 K P = K C RT ( c + d ) −( a +b ) = K C ( RT ) n
Δn : change in number of moles of gas in the reaction
Δn = (moles of gaseous products) - (moles of gaseous reactants)
Note: When Δn = 0, Kp = Kc, since RT to power of 0 = 1.
If the Kc for the chemical equation below is 0.500 at a temperature of 300. K, then what is the
Kp?
2 OF2(g) + 2 NH3(g) <—> N2F4(g) + O2(g) + 3 H2(g)
Electrochemistry
▪
Study of the relationship between chemical change and electrical
work.
Chemical Change: oxidation-reduction (redox) reaction
Electrical work: movement of electrons from one chemical species to another.
Electrochemical Cells
Galvanic Cell (Voltic Cell)
Voltaic cell based on Zn – Copper Reaction
(Electrical energy from chemical reaction)
Spontaneous
Electrochemical Cells
Electrolytic Cell
non-Spontaneous
Reduction Potential
Corrosion
Natural redox process that oxidizes metals to their oxides, sulfides and/or Carbonates
Corrosion of Copper
Corrosion of Iron
Corrosion of
Iron
1. Iron does not rust in dry air nor in air-free
water.
2. Rust distributes randomly at the surface.
3. Iron rusts more quickly at low pH (high
[H+]).
4. Iron rusts more quickly in contact with
ionic solutions.
5. Iron rusts more quickly in contact with a
less active metal (such as Cu)
6. and more slowly in contact with a more
active metal (such as Zn).
Prophylactic Protection
Applying a protective coating of another
metal that is more difficult to oxidize
Chromium (Cr)
Tin (Sn)
Corrosion Prevention
Cathodic Protection
Using a more easily oxidized metal to protect iron from corrosion
1. Zn (E° = −0.76 V for Zn2+ + 2e−→ Zn)
becomes the anode, and iron becomes the
cathode
Corrosion Prevention
Cathodic Protection
Using a more easily oxidized metal to protect iron from corrosion
2. Mg (E° = −2.37 V for Mg2+ + 2e−→ Mg)
Sacrificial Electrode
Corrosion Prevention