AP®︎ Chemistry: Topic 6.6 Flashcards

Master key terms and definitions for Topic 6.6 of AP Chemistry – Introduction to Enthalpy of Reaction to help you prep for quizzes and the AP exam.

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Term

Enthalpy Change of Reaction

Definition

Heat absorbed or released by a reaction at constant pressure, written as ΔH.

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Enthalpy Change of Reaction
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Heat absorbed or released by a reaction at constant pressure, written as ΔH.

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Molar Enthalpy of Reaction
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Enthalpy change per mole of reaction as written in the balanced equation, usually in kJ/mol.

6.6.A
Heat / q
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Thermal energy transferred between a system and surroundings, measured in joules or kilojoules.

6.6.A
q = nΔH
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Calculate reaction heat by multiplying moles of reacting substance by molar enthalpy change.

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Calculating Moles from Heat and ΔH
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Rearrange q = nΔH to n = q/ΔH, keeping units and signs consistent.

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Limiting Reactant in Enthalpy Calculations
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Use the moles of the limiting reactant to determine the total heat of reaction.

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Thermal Equilibrium After a Reaction
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Energy is exchanged until products and surroundings reach the same final temperature.

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System and Surroundings
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The reacting chemicals are the system; everything else exchanging energy with them is the surroundings.

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Potential Energy to Kinetic Energy in Reactions
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Differences in chemical potential energy appear as particle kinetic energy changes and temperature changes.

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Reactant vs. Product Enthalpy in Exothermic and Endothermic Reactions
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Exothermic products have lower enthalpy than reactants; endothermic products have higher enthalpy.

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Constant Pressure and Enthalpy
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At constant pressure, the reaction enthalpy change equals the heat transferred, q.

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Exothermic and Endothermic Reactions
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Reactions releasing heat have negative ΔH, while reactions absorbing heat have positive ΔH.

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Bond Energy Changes in Reactions
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Breaking bonds absorbs energy and forming bonds releases energy, changing chemical potential energy.

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Enthalpy
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A thermodynamic quantity representing a system’s heat content at constant pressure.

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