Chem 302 Unit 1

Because ΔH and ΔS always have the same sign, ΔG of a phase change is always

temperature dependant

-ΔG means a reaction is spontaneous

for -ΔH and -ΔS: ΔG is negative at low temps (going down a phase)

for +ΔH and +ΔS: ΔG is negative at high temps (going up a phase)

calculating a phase transition temperature:

T_phase=ΔH/ΔS

If the reaction occurs spontaneously then ΔG:

is negative/below 0

if the reaction doesn’t occur spontaneously then ΔG:

is positive/above 0

when you are at equilibrium (equally between phases) ΔG:

is 0 (definition of equilibrium)

Higher IMF means _____ vapor pressure

lower

higher temp means _____ vapor pressure

exponentially higher

vapor pressure is a _____ phenomenon

surface

vapor pressure is _____ of volume

independant, bc pressure is collisions with container

vapor pressure is measured when gas and liquid phases…

are at equilibrium

unique thing about H₂O phase diagram:

negative slope for solid/liquid line, indicated solid is less dense than liquid because ice can melt at a lower temperature when pressure is highered (think of biting an ice cube and it melts)

because of the very strong hydrogen bonds/attraction in water molecules

ΔH_vap is:

always positive

ΔH_vap of water

40 kJ/mol

ΔH_vap of of HOCH₂CH₂OH (ethylene glycol)

60 kJ/mol

ΔH_vap of C₆H₁₄ (hexane)

30 kJ/mol

ΔH_vap of helium

2 kJ/mol

at triple points on phase diagram:

all three phases in equilibrium

at lines on phase diagram:

two phases in equilibrium

Substances with large heats of vaporization produce

low vapor pressures at room temperatures.

the Clausius Clapeyron applies when:

at equilibrium when ΔG=0

For the same substance at the same temperature, vapor pressure

will always be equal

HIGHER IMF MEANS _____ VAPOR PRESSURE

LOWER

Ideal gas constant

8.3 J/mol

Higher ΔH_vap:

stronger bonds/IMFS, lower vapor pressure

the phase with the smallest heat capacity will have:

the largest slope on a heat supplied vs temp graph and increase in temp most when the same amount of heat is added