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Heat & Changes of State

Heat & Changes of State. Changes of State. Solid to liquid Liquid to solid Liquid to gas Gas to liquid. Heat & Changes of State. When a change of state occurs by a gain or loss of heat, the temp remains constant until the change of state is complete!. Molar Heat of Fusion ( ∆H fus ).

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Heat & Changes of State

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  1. Heat & Changes of State

  2. Changes of State • Solid to liquid • Liquid to solid • Liquid to gas • Gas to liquid

  3. Heat & Changes of State • When a change of state occurs by a gain or loss of heat, the temp remains constant until the change of state is complete!

  4. Molar Heat of Fusion (∆Hfus) • Fusion - when a solid absorbs heat at its freezing point • Molar heat of fusion – heat absorbed by 1 mole of a solid as it melts into a liquid (at constant temp) • ∆Hfus for water: 1 mole = 6.01kJ

  5. Molar Heat of Solidification (∆Hsolid) • Solidification - when a liquid releases heat as it turns into a solid • Molar heat of solidification – heat released by 1 mole of a liquid as it becomes a solid (at constant temp) • ∆Hsolid for water: 1 mole = - 6.01kJ

  6. ∆Hfus = - ∆Hsolid • The quantity of heat absorbed by a melting solid is the same as the heat released when a liquid solidifies H2O (s) + 6.01kJ → H2O (l) H2O (l) - 6.01kJ → H2O (s)

  7. Examples • How many grams of ice at 0°C will melt if 2.25 kJ of heat are added? • How many kilojoules of heat are required to melt a 10g popcicle at 0°C? use molar mass of water

  8. Molar Heat of Vaporization (∆Hvap) • Vaporization - when a liquid absorbs heat at its boiling point to become a vapor • Molar heat of vaporization – heat absorbed by 1 mole of a liquid as it vaporizes into a gas • ∆Hvap for water: 1 mole = 40.7kJ

  9. Molar Heat of Condensation (∆Hcond) • Condensation- when a vapor releases heat as it turns into a liquid • Molar heat of condensation – heat released by 1 mole of a vapor as it becomes a liquid • ∆Hcond for water: 1 mole = 40.7 kJ

  10. ∆Hvap= - ∆Hcond • The quantity of heat absorbed by a vaporizing liquid is the same as the heat released when a vapor condenses H2O (l) + 40.7kJ → H2O (g) H2O (g) – 40.7kJ → H2O (l)

  11. Examples • How much heat (in kJ) is absorbed when 24.8g H2O(l) at 100°C & 101.3kPa is converted to steam at 100°C ? How many kJ of heat are absorbed when 0.46g of chloroethane (C2H5Cl, bp 12.3°C) vaporizes at it normal boiling point? Molar heat of vaporization of chloroethane is 26.4 kJ/mol.

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