Chemistry 3 Flashcards
What is the relationship between the following:
- vapor pressure
- intermolecular forces
- boiling point
- ΔHvap
vapor pressure is inversely related to the following:
intermolecular forces
boiling point
ΔHvap
So, as vapor pressure DECREASES, intermolecular forces, boiling point, and ΔHvap INCREASE
What happens to the boiling point if you throw salt in water?
What about the freezing point?
Because the ion dipole is stonger than the H-bonding, the molcules will want to stay in the liquid phase more.
So:
Boiling point incrases
Freezing point decreases
Although only molecules having much great than average kinetic energy can escape liquid, the temperature of a liquid in equalibrium with its vapor is found to be the same as that of the vapor.
How can this be interpreted?
The excess kinetic energy is expended on overcoming attractive forces exerted by the molecules of the liquid.
(explains why phase changes are isothermal)
Vapor Pressure Depression (Raoult’s Law)
PA = XAPAº
- dependent on SURFACE AREA!!!
- Assumes ideal liquids without intermolecular reactions/forces
- What is the molarity? Under standard conditions shown by PAº we know that we are at 1 M concentration so the vapor pressure of A when XA = 1 (Q=1 in standard conditions)
- XA = mole fraction: ranges from 0 to 1.
molality
moles solvent / kg solent
Ex: [1 mole NaCl (s)] / [1 kg H2O] = 1 m
i
particles/ mole solute
Freezing point depression
ΔTf=iKfm
Kf is a constant for a given solvent
Boiling point elevation
ΔTb=iKbm
Kb is a constant for a given solvent
Osmotic Pressure
π=MRTi
Henry’s Law
As partial pressure of a gas decreases the partial pressure of solution drives rxn toward gas phase. So solubility decreases
CO2 (g) –>/<– CO2 (aq) + heat
ΔHsol is negative
Corrosion reaction
Metals deteriorate in corrosion reactions when a liquid or gas, usually oxygen, chemically attacks the surface of the metal.
Rusting of Iron:
Sulfur on silverware:
Decomposition reactions
Decomposition reactions occur when a compound breaks down into two or more substances, usually as a result of heating, electrolysis, or light.
*The reverse of a decomposition reaction is always a combination reaction, and vice versa.
Single displacement
Single displacement reactions occur when an atom (or ion) of one compound is replaced by an atom of another element.
Single displacement reactions are often further classified as redox reactions.
Oxidation Number Assignmet
The oxidation number is the number assigned to an atom in an ion or molecule that denotes its real or hypothetical charge.
- The oxidation number of a free element is 0.
- The oxidation number of a monatomic ion equals the charge of the ion.
- The sum of the oxidation numbers in a neutral compound is 0.
- For a polyatomic ion, the sum of the oxidation numbers equals the overall charge of the ion.
- The more electronegative element in a species is assigned its typical negative oxidation number; the more electropositive element has a positive oxidation number.
- Fluorine, the most electronegative element, always has a -1 oxidation state in its compounds.
- Oxygen, second only to fluorine in electronegativity, generally has an oxidation state of -2 in its compounds; the two exceptions are in peroxides, where the oxidation state of oxygen is -1, and in superoxides, where it is -1/2.*
- Hydrogen usually has an oxidation state of +1, except when paired with more electropositive elements, which make it have an oxidation state of -1.
redox reactions
Reduction-oxidation, or redox, reactions involve the transfer of electrons from one species to another.
