IMFs and thermodynamics

order of IMFs from strongest to weakest

ion-ion, hydrogen bonding, dipole-dipole, dispersion

polarizability

the measure of how easily the electron cloud can be distorted
more electrons=stronger polarizability
for nonpolar molec. look for longest hydrocarbon chain

ideal conditions

-no imfs between gases
-most ideal-least polarizable
-hotter temp
-low pressure

boiling point

the temp at which all IMFs break in order for a liquid to boil. Strong IMFs=Strong BP

vapor pressure

can only be determined when the rate of condensation=rate of evaporation. The higher the vapor pressure the weaker the IMFs

cohesive forces

attractions between the same molecule

adhesive forces

attractions between different molec.

surface tension:

the surface molecule has higher energy than bulk molec.
-the inward forces that must be overcome in order to expand the surface area of a liquid

viscosity

resistance to flow
-increase in temp, decrease in viscosity
-increase in molar mass, increase viscosity
-more branching, increase viscoity

molecular solids

connected though IMFs: hydrogen bonds, dipole-dipole, and dispersion
-covalent molec.
-usually MP is below 500k
ex: H2O, CO2,

ionic solids

ion-ion bonds
-hard, rigid, aqueous ionic solutions conduct electricity

covalent solids

network of covalent bonds only
-melting points above 500k
-brittle and insoluble in water
-ex: B, C, P, BN

metallic solids

held together only by metallic bonds

change in internal energy

change in U=q+w

isothermal

constant temp

adiabatic

constant heat

isobaric

constant pressure

Internal energy U

sum of Kinetic and potential energy

work

w=-P*change in V* (101.325)
-volume decrease work is positive: Work done ON system BY surrounding
-volume increase, work is negative: Work done BY system ON surrounding
also
w=-change in n*RT
positive change in n, negative w
negative change in n, postive w

heating curves

transition from solid-liquid-gas: endothermic
gas-liquid-solid: exothermic

heat energy

q=mc*change in T
use when in the same physical state
q=m*change in heat
use during phase change

heat of vaporization

heat needed to vaporize a specific amount of a substance
= -heat of condensation

heat of fusion

heat needed to melt a specific amount of substance
= -heat of freezing

heat of sublimation

=heat of fusion + heat of vaporization
- = -heat of deposition

at constant volume

change in U is equal to q

If U is positive and change in volume is positive, at constant pressure

w is negative, q is positive
q is larger here than if U is positive at constant volume

at constant pressure

q= change in H
-Change in H is the quantity of heat transferred in or out of a system as it undergoes a chemical or physical change at constant pressure

When would Change in H equal change in U at constant pressure

if w=-change in nRT, then when n=0 w=0
for change in n look at gasses only
n and w have opposite signs

Standard Enthalpy

the change in H for a reaction when all reactant and products ae in their standard states
-T=298 and P=1 atm

change in H is negative

exothermic
favorable

Standard molar enthalpy of reaction

= standard molar enthalpies of products - reactants

bomb calorimeter: constant volume

When you calculate heat (q) you are finding change in internal energy (U)

Coffee cup calorimeter: constant pressure

When you calculate heat you are finding change in H

at constant pressure

q=H

at constant volume

q=U

Hess's Law

the enthalpy change for a reaction is the same whether it occurs by one step or by a series of steps s

standard molar enthalpies of formation

1. reactants need to be elements in their standard state

2. forms only one mol of one molecule as a products -most negative standard molar enthalpies are the most favorable -elements in their standard states are 0

Enthalpy of a reaction (H)

net result of bond breaking and bond forming
(bonds broken)-(bonds formed)

bond energy

the amount of energy that must be absorbed (+) to break a specific chemical bond
-the stronger the bond the higher the bond energy

entropy

a state function that is a measure of the dispersal of energy
-the ratio of reversible heat (qrev) and temp (T)
change in S=(qrev)/T
-when positive, reaction is spontaneous

Microstate

a specific configuration of the locations and energies of the atoms or molecules that comprise a system
-molecular geometry dictates the location of the atoms
-change in S=kln(micro state final)/(micro states initial)
-when micro states increase change in S is positive
-the most probable distribution is the one with the most micro states (greatest S)

to find sign of change in S

(number of moles of gas in the products)-(moles of gas in the reactants)

2nd law of thermodynamics

All spontaneous changes are accompanied by an increase in universal entropy
-universal entropy= entropy of system + entropy of surrounding
-entropy of system does not equal -entropy of surroundings

3rd law of thermo

the entropy of a pure perfect crystalline substance at absolute zero is zero (one microstate)

absolute entropies

entropy of the reaction= (entropy of products)-(entropy of reactants)

increase in temperature

increase in entropy

increase in volume

increase in entropy

phase change

from solid to liquid to gas, increase in entropy

delta S of surroundings

-(change in H of the system)/T

mixing

increase in entropy

in an endothermic reaction

delta H, S, and q will be postive

delta S of the universe

determines spontaneity

Mercury and Br

are liquid in the standard state

Gibbs free energy

=delta H-T(delta S)
***watch units

Standard Free energy of formation (delta G)

products-reactants
-1 mol of substance formed from it's elements in their standard states

spontaneous at high T

H positive, S positive

spontaneous at low temperatures

H negative, S negative

never sponanteous

H positive, S negative

always spontaneous

H negative, S postive

to calculate MP or BP

delta H/delta S

delta S

=q/t