10.4 phase – any part of a system with uniform composition and properties. condensation – gas...

10.4

Phase – any part of a system with uniform composition and properties.

Condensation – gas changes to a liquid

Molecules of liquid can evaporate and then condense and re-enter the liquid phase

Condensation and evaporation can happen at the same rate…

Equilibrium – a dynamic condition in which 2 opposing changes occur at equal rates in a closed system

No net change in amt. of substance in either phase.

• P is directly proportional to [ ]• Equilibrium vapor pressure – pressure exerted by vapor in equilibrium with its corresponding liquid at a given temp

• Different for each liquid• The higher the bond strength, the __________the EVP

• Think about the KMT

• Volatile Liquids – liquids that evaporate readily

• __________ forces of attraction.• Boiling – conversion of a liquid to a vapor within the liquid as well as at the surface

• Boiling point – the temp at which the equilibrium vapor pressure of the liquid = atm pressure

• The ________ the atm pressure, the lower the b.p.

• Temp is constant while boiling• Normal atmospheric pressure = 1 atm, 760 torr, 101.325kPa

• E needs to be + constantly to continue boiling

MEV – the amt of E as heat that is needed to vaporize 1 mol of liquid at the liquids b.p. at constant pressure.

ΔHv Measure of attraction of particles

• Freezing – physical change of liquid to solid

• Loss of E• Freezing point – the temp at which solid and liquid are at equilibrium at 1 atm

• At f. p. particles have same amt of ave K. E.

At m.p. the solid and liquid have the same amt of k.e. also.

For pure crystalline solids, f.p. and m.p. are at the same temp.

Temp is constant until all one phase

Example: water and ice

MEF – the amount of energy as heat required to melt one mole of solid at the solid’s m.p.

ΔHf

Dependent on attractive forces b/t molecules

Sublimation – the change of state from a solid directly to a gas = CO2

Deposition – the change of state from a gas directly to a solid = Frost

Phase Diagram – a graph of pressure versus temperature that shows the conditions under which the phases of a substance exist

Triple point – indicates the temp and press conditions at which the solid, liquid, and vapor coexist at equilibrium

Critical point – indicates the critical t and critical p

Critical temperature tc – the t above which the substance cannot exist in the liquid state

Critical Pressure Pc – the lowest p at which the substance can exist as a liquid

•This is the phase diagram for water.•Notice the triple and critical points

•The Heating curve for water.•Notice the 2 flat lines

Some constant for heating curve calcualtions

Δhvap = 40.67 kJ/molΔhfus

= 6.01 kJ/molCice = 2.09 J/g* KCwater = 4.18 J/g* KCsteam = 1.84 J/g*K

Calculate the enthalpy change upon converting 1.00 mol of ice at -25°C to water vapor (steam) at 125°C under a constant pressure of 1 atmosphere.

What is the enthalpy change during the process in which 100 grams of H2O at 50.0°C is cooled to ice at – 30.0°C?

How much energy in kJ is needed to cool 385 grams of steam at 900°C to ice at -200°C?

How much energy (in kJ) is needed to convert 50.0 grams of water at 75°C to steam at 120°C?

Calculate the enthalpy change upon converting 5.00 mol of ice at -75°C to water vapor (steam) at 225°C under a constant pressure of 1 atmosphere.