Chapter 7 Phases
Heat absorbed/released vs entropy increase/decrease vs Internal KE increase/decrease 1) condensation 2)vaporization 3) crystallization 4) fusion 5) sublimation 6) deposition
1) condensation (gas to liquid) -entropy decreases -heat released (molecules not move as freely in liquid compared to gas) -KE decreases 2) vaporization/boiling (liquid to gas) -entropy increases -heat absorbed -KE increases 3) crystallization (freezing liquid to solid) -heat released -entropy decreases -KE decreases 4) Fusion (melting: Solid to liquid) -entropy increases -heat absorbed -KE increases 5) sublimation (solid to gas) -entropy increases -heat absorbed -KE increases 6) deposition (gas to solid) -entropy decreases -heat releases -KE decreases
When a substance absorbs or releases heat, one of 2 things can occur: (when to use each equation)
1) temperature increases q=mcdeltaT 2) phase change (BUT temperature is constant)
1mL= ? cm^3
1cm^3 (equivalent)
1 cal= how many Joules?
4.2 Joules (SI for energy)
Phase changes that spread molecules out, ________ heat. What are they?
ABSORB (increase entropy) 1) sublimation 2) melting/fusion 3) vaporization/boiling
Phase diagram: Boundary lines between 2 phases represents? At what pressure, will MP and BP be determined? Temp & Pressure at which all 3 phases exist? Critical point marks the end of?
Boundary: equilibrium of 2 phases 1 atm: MP between solid and liquid (halfway) BP between liquid and gas (half way) Triple Point where all 3 phases exist Critical point marks the end of the liquid-gas boundary: has both liquid (high density) and gas (low viscosity) properties -SUPERCRITICAL FLUID (cannot increase pressure to force it back into liquid phase)
Heat Capacity (C)=?
C=mc mass x specific heat
A substance's heat of vaporization is ALWAYS ________ than its heat of fusion
GREATER
Ideal pressure and temp for gas vs solid
Gas: High temp and low pressure Solid: LOW temp and high pressure
Which is likely to have the highest specific heat? a) CH4 b) (CH3)4Si c) CO d) CH3OH
IM forces: hydrogen bonding>dipole forces>dispersion forces (nonpolar molecules) stronger the force, greater the specific heat, more resistant to temperature change D has strongest IM force
How much heat is necessary to raise the temperature of 2g of solid H2O from 0 degrees celsius to 85 degrees celsius? (heat of fusion=80cal/g and specific heat=1 cal/g X Celsius)
Melting/Freezing point of water is 0 degrees Celsius (depending if raising or lowering temp) 2 processes occur 1) phase change (melting/fusion) q=n x H of fusion q1= 2 x 80= 160 2) heat from 0 to 85 degrees q2=mcdeltaT q2=2 x 1 x (85-0)= 170 so qtotal=170 + 160= 330 cal of heat total
Temperature changes only occur when there is?
NO phase change -temperature remains constant during a phase change (hence the horizontal line) -temperature increases/decreases if a phase change is NOT occurring
Because the slope of the solid-liquid boundary for water is slightly ________, this means that an increase in pressure at constant temperature favors what phase?
Negative; line invades solid portion to spread out liquid (liquid more dense than solid for water); this favors the liquid phase NOT the solid phase (as in the case of most substances) hence why increasing the pressure of solid water produces liquid water due to the negative slope (increase pressure with skating which causes ice to melt and allow skaters to glide on thin layer of liquid ice)
Phase transitions are a type of ________ change
PHYSICAL (NOT chemical)
Phase changes that bring molecules together, ________ heat. What are they?
RELEASE 1) freezing/crystallization 2) condensation 3) deposition
During a phase change, temperature __________?
STAYS CONSTANT (DURING a phase change hence why q= n x deltaH)
Heat of transition if positive? if negative?
amount of heat absorbed and released DURING a phase change q= n x deltaH of the transition q= amount of heat (calories) n= # of mols (grams) deltaH= heat of phase transition (cal/g) q and deltaH positive: heat absorbed q and deltaH negative: heat released
During a phase transition, the temperature of the substance?
does NOT change; stays constant (hence the horizontal line in the phase transition diagram)
Phase transition diagram
during phase changes, temperature is constant so q=n x heat of transition "horizontal straight line" when no phase change is occurring but temperature decreases/increases, q=mcdeltaT: "linear vertical line"
When heat is RELEASED, entropy _______ and KE _________
entropy and KE decreases (form more ordered phases)
Supercritical fluid contains properties of both?
gas (low viscosity) and liquid (high density); occurs beyond critical point
The stronger the intermolecular forces, the ________ the specific heat
greater; more resistance to temperature change and disruption
Higher temperature, _________ the average kinetic energy, the _________ its entropy
higher KE, higher S (entropy/more disorder)
Temperature is a measure of?
internal kinetic energy that molecules have
specific heat (c)
intrinsic property of a substance that tells us how resistant is is to temperature change (different for type of substance) q=mcdeltaT
What happens when a container of liquid water (holding 100 mols of H20) at 0 degrees Celsius completely freezes? (deltaH fusion=6kJ/mol and delta H vaporization= 41kJ/mol)? a) 600kJ heat absorbed b) 600kJ heat released c) 4100kJ heat released d) 4100kJ heat absorbed
liquid to solid: entropy increases and heat is released so that eliminates A and D liquid to solid is a freezing/crystallization process so deltaH vaporization is useless q=n x deltaH freezing q= 100 x 6= 600 kJ released (B)
Going up in altitude __________ atm pressure, as a result the melting point of water will?
lower atm pressure water has negative slope of solid vs liquid -as pressure decreases, temperature increases so this increases the melting point of water in places of higher altitude LOWER; melting point of water will be higher
Physical changes only affect ___________ bonds NOT __________ bonds
only affect INTERMOLECULAR bonds (dispersion forces, dipole interactions, H bonds) NOT INTRAMOLECULAR bonds (nature of individual compounds conserved with physical changes)
The melting point of Iron is 1530 degrees Celsius, and its heat of fusion is 64cal/g. How much heat would be required to completely melt 50g of Iron at 1530 degrees celsius?
phase transition: asking for heat required (calories)=q q=n x deltaH fusion q (calories)= 50g x 64cal/g= 3200cal
A phase diagram shows how phases are determined by?
pressure (y axis) and temperature (x axis)
Of the four different metals (with same amount of mass and heat added), which will exhibit the smallest change in temperature? a) Al (c=0.9) b) Pd (c=0.13) c) Sn (c=0.23) d) Fe (c=0.45)
q=mcdeltaT solve for T T=q/mc so T is inversely proportional to c (specific heat) smallest temperature change occurs with largest specific heat (A) specific heat (c): resistance to temperature change
Temperature is ________ proportional to heat absorbed and __________ proportional to specific heat
q=mcdeltaT (solve for T) DIRECTLY (increase in absorbed heat increases temperature) INVERSELY to specific heat (higher the specific heat the lower the temperature change since it is more resistant)
The heat of sublimation of water is 46kJ/mol. If heat is transferred to the sample by the environment at a rate of 0.1 kJ/min, approximately how long with it take to lyophilize 40cm^3 of frozen water? (density= 0.91g/mL) a) 7.7 hours b) 15.3 hours c) 77 hours d) 153 hours
set up conversion (1mL=1cm^3) 40mL x 0.91g/mL x 1mol H20/18gH20 x 46kJ/mol x min/0.1 kJ x 1hr/60min equals about 15 hours
The most volatile compounds have the _____________ IM forces The higher the vapor pressure the _________ the melting and boiling point
weakest! (nonpolar compounds are very volatile since they have weak IM forces) higher the VP, the lower the MP and BP (easier it is for substances to melt/boil due to weaker IM forces)
When heat is ABSORBED, entropy ________ and KE _______
when heat is absorbed (endothermic), entropy and KE INCREASE because molecules are moving more freely to create more disorder
