26-27 Flashcards
calorie to joules
4.2
Calorie is 4.2 J
Calorie > Joule
1 kCal = 4.2 (10)^3 joules
standard conditions versus STP (IMPORTANT)
1 ATM, 298 K
STP (standard temperature and pressure) is 273 K!
heat of formation (∆H*_f )
O2, H2, Cl2 are naturally diatomic
O2 = 0 O = 249 kJ/mol (energy needed to break the bond)
homolytic cleavage (Bond Dissociation Energy)
the stronger the bonds of the formed product (less enthalpy), the more exothermic
STRONGER BONDS = REDUCED ENTHALPY = EXOTHERMIC
heat of reaction
Bonds broken - Bonds formed
heat of fusion
solid to liquid
“fusing solid into liquid”
heat is RELEASED when steam CONDENSES into liquid
rules for entropy (IMPORTANT)
- Gases > liquids > solids (CHECK THIS! this is important!)
- particles in solution > solids
- 2 moles > 1 mole
Ice -> Liquid -> Gas
ENDOTHERMIC, gas has higher enthalpy than ice
gas condenses to liquid, crystalizes to solid (EXOTHERMIC)
sublimation/deposition
deposition: Heat released, Internal KE decreases, entropy decreases
fusion
SOLID to LIQUID (“fusive liquid”)
phase diagram for water
solid-liquid line is NEGATIVE slope due to denser liquid phase than solid
gas to liquid to solid (remember thing significant changes)
HEAT is RELEASED
Internal KE decreases
Entropy DECREASES
Ideal gas assumptions
- molecules are small = no volume
- collisions mean pressure
- no intermolecular forces
- KE of molecules is proportional to Temp
1 atm = 101.3 kPa
760 mm Hg or 760 torr
1 atm approximately 1 barr
PV = nRT (what is R) (IMPORTANT!)
0.0821
Charles’s law
temperature increases volume
Pressure = CONSTANT
Boyle’s law
PV is constant
“Boyle PV”
Constant Temperature
Gay-Lussac
Temperature and pressure in constant volume
Equal-volume containers, same temperature and pressure
SAME n MOLES of compound
At 0˚C and 1 atm, 1 mole of gas occupies…
22.4 L
deviations from ideal gas law
P_real < P_ideal (intermolecular forces)
volume_real < V_ideal (the particles take up empty space)
more ideal if the particle is SMALL
higher temperature = MORE IDEAL (low temperature causes condensation, which is more like liquid)
LOWER PRESSURE = MORE IDEAL (high pressure causes intermolecular mores, limits volume of actual empty space)
Polyatomic OCCUPY MORE VOLUME than monoatomic, even CH4 (16) and Ar (40 amu)
x
Partial pressure is related to MOLE FRACTION
if total pressure is 8 atm and Particle_A is 1/2 total moles, then Particle_a has 4 atm partial pressure
rms
KE is proportional to Temperature for ALL molecules in a gas
1/2mv^2 = 1/2mv^2
smaller mass, faster particle
RMS is the (larger/smaller)^1/2
(Memorize: Graham’s law of effusion p. 754)
Q: SOLIDS are least entropic
Solids are not necessarily polar/ionic
