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Endothermic and Exothermic Processes

▶︎  Watch it animatedinteractive step-through · ~3 min · optional

A process is endothermic if the system absorbs energy from its surroundings (ΔH > 0) and exothermic if it releases energy (ΔH < 0). The sign of the enthalpy change, ΔH, is defined from the system's point of view. Energy is transferred between system and surroundings — never created or destroyed.

UNIT 6 TOPIC 6.1 • ENDOTHERMIC AND EXOTHERMIC PROCESSES ENERGY FLOW ENDOTHERMIC PROCESS System absorbs energy from surroundings ΔH > 0 energy in enthalpy reaction progress reactants products ΔH > 0 EXOTHERMIC PROCESS System releases energy to surroundings ΔH < 0 energy out enthalpy reaction progress reactants products ΔH < 0 ENERGY LEDGER RULE Breaking attractions or bonds absorbs energy · Forming attractions or bonds releases energy Dissolving may be endothermic or exothermic, depending on relative interaction strengths. TAKEAWAY Sign of ΔH describes heat flow for the system: positive = energy in, negative = energy out. AP Chemistry · Unit 6 · Thermodynamics
Energy flows between a system and its surroundings. An endothermic process absorbs energy (ΔH > 0); an exothermic process releases energy (ΔH < 0). The sign of ΔH is defined from the system's point of view, and energy is transferred, never used up.
Energy Flow · Open the sandbox →

The traps invert the sign convention (exothermic is negative ΔH, not positive), imagine energy is 'used up' rather than transferred, and assume only chemical reactions have enthalpy changes (physical processes do too). Keep the system's perspective and track where the energy goes.

The work

3 ways in · any order
Lesson
Endo- and Exothermic ›

Endothermic absorbs energy (ΔH > 0); exothermic releases it (ΔH < 0), from the system's viewpoint. The lesson tracks energy flow and the sign convention, then closes with a ten-scenario check.

Skill check · 10 scenarios
Open lesson →
Diagnostic
10-item topic check ›

Ten items spanning the Topic 6.1 misconceptions: the exothermic direction inverted, energy imagined to be used up, only reactions credited with enthalpy changes, and thermal equilibrium misread.

Not started · 10 items · ~15 min
Start diagnostic →
Targeted Practice
Drill a single misconception ›

Pick one of the failure modes you missed and drill it on its own. The round is adaptive: two correct in a row clears the misconception and moves you to the next.

Take the diagnostic to identify your misconceptions
Diagnostic first