Gen Chem 2 Exam 1

Prefixes (conversion)

mega (M)- 10^6

kilo (k)- 10^3

deka (da)- 10

deci (d)- 10^-1

centi (c)- 10^-2

milli (m)- 10^-3

micro (the weird u symbol)- 10^-6

nano (n)- 10^-9

pico (p)- 10^-12

Charges on Periodic table

metals & non metals on periodic table

sig figs in multiplication and division

determined by original number that has smallest # sig figs

• 4.242 x 1.23 = 5.21766 → SIG FIGS → real answer: 5.22

sig figs in addition and subtraction

-least # of decimal places

• 142.5 + 2.67 → use 142.5 → answer w ONE decimal place

Phase

physically distinct, homogeneous part of a system e.g. liquid water, ice, water vapor

Potential Energy

attractive forces draws particles together

Kinetic energy

disperses particles (repels)

Gas Volume/Shape

• no fixed shape or volume

Liquid Volume/Shape

• fixed volume, no fixed shape

solid to liquid

melting

liquid to solid

freezing

gas to liquid

vaporization

liquid to gas

evaporation

solid to gas

sublimation

gas to solid

deposition

endothermic

• system absorbs heat

• surroundings temp decreases

• Delta H > o

exothermic

• system releases heat

• temp or surroundings raises

• Delta H < 0 (negative)

endothermic phases

sublimation, melting, vaporization

exothermic phases

freezing, condensation, deposition

Heating- Cooling Curve

label

Mark these sections on phase diagram

What phases on heating cooling curve have constant T/ 2 phases

2,4

What phases on heating cooling curve have changing T/ 1 phase

1, 3, 5

Hess Law

1. Identify the target equation, the step whose ΔH is unknown

   1. Note the amounts of each reactant and product

2. Manipulate each equation with known ΔH values so that the target amount of each substance is on the correct side of the equation

   1. Change the sign of ΔH when you have to reverse the  equation

   2. Make sure to multiply the number of moles and ΔH by the same factor

3. Add  the manipulated equations and their resulting ΔH values to get the target equation and its ΔH

   1. All substances, except those in the target equation, MUST cancel

Which is phase diagram for water

Density formula

-D=mass/volume

-g/mL (solid/liquid)

-g/L (gas)

how would you solve

how would you solve

what formula do you use for transition 2 phases happening at constant T

what formula do you use for heating/cooling of 1 phase causing change in T

dynamic equilibrium

molecules are leaving and entering the liquid at the same rate

What happens at equilibrium

the vapor pressure is constant

boiling point of liquid is temp where

Vapor prssure = external pressure

normal boiling point of a substance is observed at

760 torr = 1 atm

Evaporation vs Boiling

Factors affecting vapor pressure

• Temperature

  • higher temp = higher pressure bc more KE

• IMF

  • less intermolecular forces = higher pressure

    • bc weaker forces = more easily molecules can leave liquid & enter gas phase

Units of this

how would you solve

∆Hvap

Hfinal – Hinitial = Hvapor – Hliquid

∆Hvap at critical point

0 kJ/ mol

Heating-cooling curve shows…

• T vs. heat

• shows the change in T of a substance when it absorbs or releases heat. Within a phase, T changes. During a phase change, T is constant

Phase diagram shows…

• P vs. T: shows which phase exists under given set of P & T, P & T for phase transition, and critical and triple points

Lewis Dot Structure Steps

1. find total valence e- (group #)

2. draw skeleton structure w/ single bonds

3. assign remaining valence e-

   1. make multiple bonds if octet rule not satisfied

Intermolecular vs Intramolecular

• Intermolecular forces are attractive, determine physical properties,

  different for each phase

• Intramolecular forces are attractive, determine chemical properties,

  • the same for each phase e.g. H2O molecules are present in water, ice, and vapor

3 intramolecular forces

ionic bond, covalent bond, metallic bond

ionic bond

metal + nonmetal

covalent bond

nonmetal + nonmetal

metallic bond

metal + metal

3 types intermolecular forces

1) hydrogen

2) dipole- dipole

3) dispersion

whats strongest & weakest intermolecular

• h bonding strongest

• dispersion weakest

Hydrogen bonds

• H bonds have HIGH bp

• H bonded to N, O, F, S, Cl

H bonding of water

• high heat capacity of water

  • moderates T changes on Earth

• high heat of vaporization

  • stabilizes our body T

• ice is less dense than water

  • prevents whole lake from freezing

Dipole dipole

• pair of equal but oppositely charged poles separated by distance

• Caused by electronegativity

electronegativity

• the ability of a bonded atom to attract shared electrons (tug of war)

• Increases up and to right

• stronger forces = higher BP

Dipole moment

charge x distance

when are dipole dipole present

in POLAR molecules only!

Dispersion forces

• always present

Identifying IMF’s

• Determine if polar or non polar

• If H bonded to N, O, F, S, Cl → hydrogen bonding

• If nonpolar → dispersion only

• if polar → london dispersion, dipole dipole

how to determine if polar or nonpolar

• non polar:

  • central atom has NO lone pairs & surrounding atoms are the same

  • Single elements are always nonpolar (He2, N2, etc)

• If it is only C & H- nonpolar & LDF only

Polarizability

• ability to distort electron cloud

• Focus on atomic size!

  • smaller size = less polarizable

  • larger size = more polarizable

• more e- = more mass = higher BP

Cylinder A: Bp is -34

Cylinder B: Bp is -188

1) polar or nonpolar?

• both nonpolar

2) look at electrons

• Cl has more e- → more forces → higher bp

3) -34= Cl2 -188= F2

When comparing substances with similar molar masses (or #e-):

• presence of H bonding & dipole-dipole INCREASES mp,bp, ∆Hvap

solve

When comparing substances with widely different molar masses (or #e-):

dispersion forces between larger molecules will increase mp, bp, ∆Hvap (see also CH3F vs. CCl4)

solve

• Cl has more e- than CH3 but its lower because (CH3)2 CO has more IMF present

which IMF explained by coulombs law

• H bonding

• dipole dipole

which IMF explained by quantum mechanical theory

• dispersion

Surface tension

• Surface molecules experience a net attractive intermolecular forces downward. This causes a liquid surface to have the smallest area possible.

• An interior molecule is attracted by others on all sides.

• weird y is the nrd req to increase surface area of liquid

• higher IMF= higher weird Y

• higher Temp = lower weird Y

Capillary Action

• rising of a liquid through a narrow opening against the pull of gravity

• occurs when adhesion forces to the walls are stronger then the cohesive forces between the liquid molecules.

The _____ of rising liquid depends upon the _____ of liquid, which the _____ will lift.

• The height of rising liquid depends upon the weight of liquid, which the surface tension will lift.

Concave meniscus

F adh > F Coh

Convex meniscus

F adh < Fcoh

Cohesive Forces

intermolecular forces between LIKE molecules

Adhesive Forces:

intermolecular forces between UNLIKE molecules

when Fadh > F Coh

• adhesion of H2O to the surface is stronger then H2O...H2O attractions

• hydrophillic surface

when Fadh < FCoh

• adhesion of H2O to the surface is weaker then H2O...H2O attractions

• hydrophobic surface

Viscosity

• resistance of a fluid to flow due to the intermolecular attractions that impede the movement of molecules around and past each other

• high visc= honey

• low visc= water

• higher IMF = Higher visc.

• Higher temp= lower visc.

Crystalline solid

particles arranged in a long- range periodically repeating 3-D geometric array, the crystal lattice (diamond, quartz, sugar, salt)

Polycrystalline

Made of variously oriented crystals (short-range order) that are separated by grain boundaries (metals, ceramics, rocks, ice)

Amorphous

articles are not organized in a definite lattice pattern (glass, plastic, wax, rubber, wax, metals can be made amorphous)

identify which solid is which

Unit Cell

the smallest portion of a crystal lattice that yields the crystal if repeated in all directions

simple cubic unit cell

• 8 x 1/8 particle =
  1 particle in one
  unit cell,

• 52 % of unit-cell

  volume occupied

body centered unit cell

• 8 x 1/8 + 1 particle=
  2 particles in one
  unit cell

• 68 % of unit-cell

  volume occupied

face centered unit cell

• 8 x 1/8 + 6 × ½ =
  4 particles in one
  unit cell

• 74 % of unit-cell

  volume occupied

Solution

homogenous mixture of two or more substances

anything + liqud =

liquid

_____ + _____ = Solution

solute + solvent

Solute

substance dissolving (sugar)

solvent

liquid substance dissolves in (water)

general rule of solubility

• Like dissolves like

• polar compounds dissolve in polar solvents

• nonpolar compounds dissolve in nonpolar solvents

salts dissolve bc….

strong ion-dipole intermolecular forces

Predicting the solubility of compounds in water and hexane

solubility & temps

• most solids more soluble at higher T

• Gases are less soluble at higher T

Unsaturated solution

• contains less than the maximum amount of solute that is capable of being dissolved

• more solute can be dissolved

Saturated solution

• contains the maximum amount of solute that can be dissolved under the condition at which the solution exists

• no more solute will dissolve

supersaturated solution

• contains more than the maximum amount of solute that is capable of being dissolved at a given temperature

• becomes unstable

  • crystals form

label

• if solution @ 40 C, most u can dissolve is approx 13 g