Heat & Changes of StateHeat & Changes of State

Changes of StateChanges of State

Solid to liquidSolid to liquid

Liquid to solidLiquid to solid

Liquid to gasLiquid to gas

Gas to liquidGas to liquid

Heat & Changes of StateHeat & Changes of State

When a change of When a change of state occurs by a state occurs by a gain or loss of gain or loss of heat, the temp heat, the temp remains constant remains constant until the change of until the change of state is complete!state is complete!

Molar Heat of Fusion (Molar Heat of Fusion (∆H∆Hfusfus))

Fusion - when a solid absorbs heat Fusion - when a solid absorbs heat at its freezing pointat its freezing point

Molar heat of fusionMolar heat of fusion – heat – heat absorbed by 1 mole of a solid as it absorbed by 1 mole of a solid as it melts into a liquid (at constant melts into a liquid (at constant temp)temp)

∆∆HHfusfus for water: 1 mole = 6.01kJ for water: 1 mole = 6.01kJ

Molar Heat of Solidification Molar Heat of Solidification ((∆H∆Hsolidsolid))

Solidification - when a liquid Solidification - when a liquid releases heat as it turns into a solidreleases heat as it turns into a solid

Molar heat of solidificationMolar heat of solidification – heat – heat released by 1 mole of a liquid as it released by 1 mole of a liquid as it becomes a solid (at constant temp)becomes a solid (at constant temp)

∆∆HHsolidsolid for water: 1 mole = - 6.01kJ for water: 1 mole = - 6.01kJ

∆∆HHfus fus = - ∆H= - ∆Hsolidsolid

The quantity of heat absorbed by a The quantity of heat absorbed by a melting solid is the same as the heat melting solid is the same as the heat released when a liquid solidifiesreleased when a liquid solidifies

HH22O O (s)(s) + 6.01kJ + 6.01kJ → → HH22O O (l)(l)

HH22O O (l) (l) - 6.01kJ - 6.01kJ → → HH22O O (s)(s)

ExamplesExamples

How many grams of ice at 0How many grams of ice at 0°C will °C will melt if 2.25 kJ of heat are added?melt if 2.25 kJ of heat are added?

How many kilojoules of heat are How many kilojoules of heat are required to melt a 10g popcicle at required to melt a 10g popcicle at 00°C? use molar mass of water°C? use molar mass of water

Molar Heat of Vaporization Molar Heat of Vaporization ((∆H∆Hvapvap))

Vaporization - when a liquid Vaporization - when a liquid absorbs heat at its boiling point to absorbs heat at its boiling point to become a vaporbecome a vapor

Molar heat of vaporizationMolar heat of vaporization – heat – heat absorbed by 1 mole of a liquid as it absorbed by 1 mole of a liquid as it vaporizes into a gas vaporizes into a gas

∆∆HHvapvap for water: 1 mole = 40.7kJ for water: 1 mole = 40.7kJ

Molar Heat of Condensation Molar Heat of Condensation ((∆H∆Hcondcond))

Condensation- when a vapor Condensation- when a vapor releases heat as it turns into a releases heat as it turns into a liquidliquid

Molar heat of condensationMolar heat of condensation – heat – heat released by 1 mole of a vapor as it released by 1 mole of a vapor as it becomes a liquidbecomes a liquid

∆∆HHcondcond for water: 1 mole = 40.7 kJ for water: 1 mole = 40.7 kJ

∆∆HHvap vap = - ∆H= - ∆Hcondcond

The quantity of heat absorbed by a The quantity of heat absorbed by a vaporizing liquid is the same as the vaporizing liquid is the same as the heat released when a vapor condensesheat released when a vapor condenses

HH22O O (l)(l) + 40.7kJ + 40.7kJ → → HH22O O (g)(g)

HH22O O (g) (g) – 40.7kJ – 40.7kJ → → HH22O O (l)(l)

ExamplesExamples

How much heat (in kJ) is absorbed when How much heat (in kJ) is absorbed when 24.8g H24.8g H22OO(l)(l) at 100 at 100°C & 101.3kPa is °C & 101.3kPa is converted to steam at converted to steam at 100100°C ?°C ?

How many kJ of heat are absorbed when How many kJ of heat are absorbed when 0.46g of chloroethane (C0.46g of chloroethane (C22HH55Cl, bp 12.3°C) Cl, bp 12.3°C) vaporizes at it normal boiling point? Molar vaporizes at it normal boiling point? Molar heat of vaporization of chloroethane is 26.4 heat of vaporization of chloroethane is 26.4 kJ/mol.kJ/mol.