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Phase Changes Involving Solids

Phase Changes Involving Solids. Melting point : temperature at which melting occurs. Same as freezing point! Enthalpy of fusion , D H fusion , is the quantity of heat required to melt a given amount (one gram, one mole) of solid. Sublimation : transition of solid  vapor.

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Phase Changes Involving Solids

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  1. Phase Changes Involving Solids • Melting point: temperature at which melting occurs. • Same as freezing point! • Enthalpy of fusion, DHfusion, is the quantity of heat required to melt a given amount (one gram, one mole) of solid. • Sublimation: transition of solid  vapor. • Example: frost disappearing from window below 0 oC • Enthalpy of sublimation, DHsubln, is the sum of the enthalpies of fusion and vaporization. • Triple point: vapor pressure curve and sublimation curve meet. • All three phases are in equilibrium.

  2. Some Enthalpies of Fusion

  3. Heating Curve For Water …until the solid begins to melt, at which time the temperature is constant… The temperature of the solid increases… …until all the solid is melted. The temperature begins to rise again.

  4. Cooling Curve For Water Temperature remains constant at the freezing point, until… Temperature drops as liquid water cools. …all the liquid solidifies, then the temperature of the solid drops. If the liquid is cooled carefully, it can supercool.

  5. How much energy is required to heat 5.0g ice at -4⁰C to liquid water at 25⁰C?

  6. Is 150kJ enough energy to boil 60.0g water that starts as ice at 0⁰C?

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