AP®︎ Chemistry: Topic 6.5 Flashcards

Master key terms and definitions for Topic 6.5 of AP Chemistry – Energy of Phase Changes to help you prep for quizzes and the AP exam.

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Term

Heating Curve

Definition

A graph of temperature versus heat added showing warming slopes and flat phase-change plateaus.

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Heating Curve
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A graph of temperature versus heat added showing warming slopes and flat phase-change plateaus.

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Cooling Curve
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A graph of temperature versus heat removed showing cooling slopes and flat phase-change plateaus.

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Phase Changes and Energy Direction
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Melting and vaporization absorb heat; freezing and condensation release heat.

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Constant Temperature During a Phase Change
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A pure substance’s temperature stays unchanged while added or removed energy changes its phase.

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Molar Enthalpy of Fusion and Vaporization
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The energy per mole required to melt or vaporize a substance at constant temperature.

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Complementary Phase-Change Enthalpies
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Opposite phase changes have equal magnitudes and opposite signs, such as vaporization and condensation.

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Phase-Change Heat Calculation
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Use q = nΔH for phase changes, with moles times the molar enthalpy.

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Heating and Cooling Curve Calculations
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Use q = mcΔT on slopes and q = nΔH or mH on plateaus, then sum steps.

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Heat of Vaporization vs Heat of Fusion
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Vaporization usually requires more energy than melting because more intermolecular attractions must be overcome.

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Molar Enthalpy of Condensation and Freezing
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The energy released per mole when a gas condenses or a liquid freezes.

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