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, kPa 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.  ΔH v  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.  ΔH f  Dependent on attractive forces b/t molecules

 Sublimation – the change of state from a solid directly to a gas = CO 2  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 t c – the t above which the substance cannot exist in the liquid state  Critical Pressure P c – 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  Δh vap = kJ/mol  Δh fus = 6.01 kJ/mol  C ice = 2.09 J/g* K  C water = 4.18 J/g* K  C steam = 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 H 2 O 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.