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Latent Heat

Latent Heat. Solid. Gas. Phases of Matter. The properties of solids, liquids, and gases differ. How does matter change state?. Liquid. Watched Pot. You want to cook a pot of potatoes in boiling water. To use energy most efficiently, you should

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Latent Heat

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  1. Latent Heat

  2. Solid Gas Phases of Matter • The properties of solids, liquids, and gases differ. • How does matter change state? • Liquid

  3. Watched Pot • You want to cook a pot of potatoes in boiling water. To use energy most efficiently, you should • A) Heat it up quickly and leave it at a full boil • B) Heat it up slowly and turn it up to a full boil • C) Heat it up quickly and turn it down to simmer • D) Heat it up slowly and leave it at a low boil

  4. Energy of Phase • Internal energy can be stored as bonds between atoms and molecules. • Solids have the strongest bonds • Energy required to break them to a liquid

  5. Heat of Transformation • As a system reaches the point of a phase change heat no longer changes the temperature. • The heat is used to change the phase. heat of fusion heat of vaporization

  6. The heat of transformation per unit mass is called the latent heat (L). Measured in J/kg It takes as much energy to melt 1 g of ice as it does to raise the temperature from 0 C to 80 C. Material (f or v)Latent Heat Mercury (f) 11.3 kJ/kg Lead (f) 24.7 kJ/kg Uranium (f) 82.8 kJ/kg Copper (f) 205 kJ/kg Water (f) 334 kJ/kg Oxygen (v) 213 kJ/kg Water (v) 2300 kJ/kg Latent Heat

  7. Phase Diagrams • For each temperature and pressure a material is in a specific state. • The triple point is uniquely defined for each material. • P3 for water is used to define the Kelvin • The critical point is where there is no difference between liquid and gas. Phase diagram for water

  8. Sublimation • At low pressures a solid can go directly to a gas and vice versa. • This process is called sublimation. • Dry ice to gaseous carbon dioxide • Water vapor to frost • There is a latent heat of sublimation Phase diagram for carbon dioxide

  9. 200 g of ice at -10 C is added to 1.0 kg of water at 15 C. Is there enough ice to cool the water to 0 C? Find the amount of heat needed to bring the ice to 0 C and melt it. Qi = mcDT + mLf Qi = 70.9 kJ Find the heat needed to cool the water down to 0 C. Qw = mcDT Qw = 62.8 kJ Yes, there’s enough ice. Summer Cooler next

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