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CHANGE IN PHASE – occurred whenever the supplied heat energy is enough to overcome the intermolecular forces of attraction - occurred at specific temperatures.

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Presentation on theme: "CHANGE IN PHASE – occurred whenever the supplied heat energy is enough to overcome the intermolecular forces of attraction - occurred at specific temperatures."— Presentation transcript:

1 CHANGE IN PHASE – occurred whenever the supplied heat energy is enough to overcome the intermolecular forces of attraction - occurred at specific temperatures (freezing/melting temperatures) and (boiling/condensation temperatures)

2 PHASE CHANGE FACTORS AFFECTING AMOUNT OF HEAT ENERGY (H) NEEDED:
1. AMOUNT OF MATERIAL (m = mass) 2. TYPE OF PHASE CHANGE (dependent on material present) FORMULA: Q = ΔH = Hp m Hp is equal to Hf = heat of fusion (melting) -Hf = heat of freezing Hv = heat of vaporization -Hv = heat of condensation

3 Melting Points and Heat of Fusion
Substance Melting point K Melting point °C Heat of fusion (1 J/g) Helium 3.5 5.23 Hydrogen 13.84 58.6 Nitrogen 63.18 25.5 Oxygen 54.36 13.8 Ethyl alcohol 159 -114 104.2 Mercury 234 -39 11.8 Water 273.15 0.00 334 Sulfur 392 119 38.1 Lead 600.5 327.3 24.5 Antimony 903.65 630.50 165 Silver 960.80 88.3 Gold 64.5 Copper 1356 1083 134

4 Heat of vaporization ( J/g)
Boiling Points and Heat of Vaporization Substance Boiling point K Boiling point °C Heat of vaporization ( J/g) Helium 4.216 20.9 Hydrogen 20.26 452 Nitrogen 77.34 201 Oxygen 90.18 213 Ethyl alcohol 351 78 854 Mercury 630 357 272 Water 373.15 100.00 2256 Sulfur 717.75 444.60 326 Lead 2023 1750 871 Antimony 1713 1440 561 Silver 2466 2193 2336 Gold 2933 2660 1578 Copper 2840 2567 5069

5 Negative sign indicates exothermic reaction
CHANGE IN PHASE What is the amount of heat energy needed to change 200 g of water at 0oC to ice? (Hf ice = 334 J/g) SOLUTION: Q = ΔH = Hf m = (-334 J/g) (200g) = J Negative sign indicates exothermic reaction

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