handouts lecture # 7 current gkfd

8/9/2019 Handouts Lecture # 7 Current GKFD

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Lecture # 7

Chapter # 5, pages 206-211; chapter # 10 pages 482-485

Exercises: 43, 50 page 240; 7, 65, 73 pages493-496

Melting(fusion): transition of solidliquid.

Melting point: temperature at which melting occurs. Sameas freezing point!

Enthalpy of fusion, H!usi", is the quantity of heat required (melting isendothermic process) to melt a set amount (one gram, one mole) of solid.

Enthalpy or heat of fusion$!usi":$2%&s' ( $2%&)'; $!usi"* +601 ./")

Freezing is exothermic processamount of heat released when a given amount ( mole)

of liquid is frozen.Enthalpy or heat of freezing$!reeig:

$2%&)' ( $2%&s'; $!reeig* - 601 ./") Sublimation: transition of solidvapor.

"ample: #ce cu$es slowly %disappear& in the freezer. Enthalpy of sublimation, Hsu), is the sum of the enthalpies of fusion and

vaporization ' amount of heat required to transform a given amount ( mole) of

solid su$stance directly to gas.Enthalpy or heat of sublimation$su) * $!usi"+ $apSublimation is endothermic process

Depositionis the reverse process, the condensation of vapor to a solid (e"othermic). phase diagram is a graphical representation of the conditions of temperature and

pressure under which a su$stance e"ists as a solid, liquid, a gas, or some com$ination ofthese in equili$rium.

*, solid'vapor equili$rium (su$limation curve). ' +riple point: all three phasessolid, liquid, vaporare in equili$rium., solid'liquid equili$rium (fusion curve).-, liquid'vapor equili$rium (vapor pressure curve)


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C"")ig cure "! ater1 +he liquid water cools until

2 the freezing point is reached, at which time the temperature remains constantas solid forms.

3 #f the liquid is cooled carefully, it can supercool.4 /nce all of the liquid has solidified, the temperature again drops.

$eatig cure "! ater. +he temperature of the solid increases as it is heated

0. until the solid $egins to melt, at which time the temperature remains constant

1. until all the solid is melted, at which time the temperature again rises.

0 12

0

1


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We can examine phase changes indetail by looking at a heating-cooling curve for a particularsubstance, which shows thechanges that occur when heat isadded to or removed from the

system at a constant rate.

3se the following data to s4etch a

cooling curve for 0.5 mole of

water. 6tart curve at 718- and end at '28-.

tep i

c"")ig cure

Ti,

C

T!,

9C Calculate Energy q, .

hases (/ne or

two: specify each

as as s, l, g)

-ooling gas 18 88 q heat n " -p(gas)" +

q 0.58 mol " 11. ;


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Exercise # 1

Ghat happens if we heat up a $loc4 of ice 8.8 4g from '8.8 H- to $oilingpoint 88.8 H- and convert to vaporI

. Garming the ice.

0. Eelting the ice.


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1. ?eating the liquid

2. *oiling point (evaporation)

handouts lecture # 7 current gkfd

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