States of Matter / IMF Flashcards
Heating Curve
Shows changes in phase as heat is added and temperature increases
Calculating Heat in Temp. Change
Q = mCpAT
Calculating Heat Solid to Liquid
Q = mHf
Calculating Heat Liquid to Gas
Q = mHv
Intermolecular Forces (IMF)
Gasses don’t have IMFs
Gasses are made by breaking IMF
Three types of IMF : London Dispersion, Dipole-Dipole, Hydrogen Bond Forces (AKA “Hydrogen Bonds”)
Forces between molecules (covalent compounds)
IMF holds liquids and solids together (gives liquids and solids definite volume, and holds together the particles)
Evaporation
Breaks IMF
Only happens at the surface of a liquid
Occurs at any temp. even cold ones
Evaporation is a COOLING process
London Dispersion Forces
Weakest of the IMF types
Temporary
Form from nonpolar (pure) molecules
Break down easily, evaporate easily
Become gasses at room temp. (Ex. liquid nitrogen)
Are solids and liquids at cold temps.
All diatomics are held together by this IMF force
Dipole-Dipole Forces
Medium strength IMF force
Forms from polar molecules
Liquids at room temp.
Alcohols typically have this IMF force
diPOL = POLar
Nonpolar (pure) Molecules
Symmetrical
NO LONE PAIRS ON CENTRAL ATOM
2 atoms, subtract electronegativity with a difference of 0.0 - 0.4
Polar Molecules
Asymmetrical
LONE PAIRS ON CENTRAL ATOM
2 atoms, subtract electronegativity with a difference of 0.5 - 1.6
Hydrogen Bond Forces
Special kind of Dipole force
Strongest IMF
Extremely polar molecules
Huge difference in electronegativity
When H bonds with either N, O, or F it is hydrogen bonding
Boiling Points
Temperature at which something boils (IMFs break)
Molecules with strong IMFs have higher boiling points
If they have the same IMF than molecules with higher molar mass
Vapor Pressure
Vapor = Gas formed when liquid evaporates
Vapor pressure = Pressure exerted by vapor particles
Easy to evaporate (weakest IMF)
If they have the same IMF than molecules with lowest molar mass
Enthalpy
The energy stored in bonds
(delta)H = Hproducts - Hreactants
Exothermic:
Change is negative
Reactants –> Products + Heat
Endothermic:
Change is positive
Reactants + Heat –> Products
1st Law of Thermodynamics
Universe favors a DECREASE (exothermic) in enthalpy
