This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? The requirement for continuous light input to produce glucose in photosynthesis shows energy absorption from the surroundings (light) into chemical bonds, classifying it as endothermic. Choice B correctly classifies the reaction as endothermic by properly interpreting the energy transfer direction from the need for light input. Choice A fails by labeling it exothermic, ignoring that light absorption indicates endothermic. The exothermic vs endothermic identification strategy: (1) Look for temperature change observations: Did temperature increase (solution got warmer, beaker hot to touch)? → EXOTHERMIC (reaction released heat to surroundings). Did temperature decrease (solution got colder, beaker cool to touch)? → ENDOTHERMIC (reaction absorbed heat from surroundings). No thermometer? Use your hand—does it feel warm (exo) or cool (endo)? (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy). (3) Check examples: combustion/burning (exo), photosynthesis (endo), ice melting (endo), hand warmers (exo), cold packs (endo), respiration (exo). Recognizing common examples helps! Memory tricks: EXOthermic = EXITs energy = energy comes OUT (releases to surroundings). ENDOthermic = energy goes IN = reaction absorbs energy (takes IN from surroundings). Or: EXOthermic = external gets hot (surroundings warm up). ENDOthermic = internal needs heat (reaction needs energy absorbed). Temperature thinking: the SURROUNDINGS' temperature change tells you the direction! If you touch the beaker and it's hot, the reaction GAVE heat to the beaker (exothermic). If the beaker is cold, the reaction TOOK heat from the beaker (endothermic). You're measuring the surroundings, which tells you what the reaction did: released (exo) or absorbed (endo) energy! Photosynthesis is a classic— you're growing your knowledge!

This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? The bright light and warming air near the flame show energy release as heat and light to surroundings, making the reaction exothermic. Choice B correctly classifies the reaction as exothermic by properly interpreting the heat and light as released energy. A distractor like Choice A fails by calling it endothermic despite energy release signs, but endothermic absorbs energy, often cooling things—keep that distinction clear! The exothermic vs endothermic identification strategy: (1) Look for temperature change observations: Did temperature increase (solution got warmer, beaker hot to touch)? → EXOTHERMIC (reaction released heat to surroundings). Did temperature decrease (solution got colder, beaker cool to touch)? → ENDOTHERMIC (reaction absorbed heat from surroundings). No thermometer? Use your hand—does it feel warm (exo) or cool (endo)? (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy). (3) Check examples: combustion/burning (exo), photosynthesis (endo), ice melting (endo), hand warmers (exo), cold packs (endo), respiration (exo). Recognizing common examples helps! Memory tricks: EXOthermic = EXITs energy = energy comes OUT (releases to surroundings). ENDOthermic = energy goes IN = reaction absorbs energy (takes IN from surroundings). Or: EXOthermic = external gets hot (surroundings warm up). ENDOthermic = internal needs heat (reaction needs energy absorbed). Temperature thinking: the SURROUNDINGS' temperature change tells you the direction! If you touch the beaker and it's hot, the reaction GAVE heat to the beaker (exothermic). If the beaker is cold, the reaction TOOK heat from the beaker (endothermic). You're measuring the surroundings, which tells you what the reaction did: released (exo) or absorbed (endo) energy! You're building strong skills—keep going!

This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? The hand warmer's temperature rose from 20°C to 41°C without external heating—the iron oxidation reaction releases energy to the surroundings, making this clearly EXOTHERMIC with energy flowing FROM the system TO the surroundings (warming the packet and nearby air). Choice B correctly identifies this as exothermic: energy flows from the system to the surroundings, which explains the temperature increase and why your hands feel warm when holding the packet. Choice A incorrectly calls it endothermic despite the warming; Choice C mislabels it as endothermic while describing exothermic energy flow; Choice D ignores the clear evidence of energy release. The exothermic vs endothermic identification strategy: (1) Look for temperature change observations: Did temperature increase (solution got warmer, beaker hot to touch)? → EXOTHERMIC (reaction released heat to surroundings). Did temperature decrease (solution got colder, beaker cool to touch)? → ENDOTHERMIC (reaction absorbed heat from surroundings). No thermometer? Use your hand—does it feel warm (exo) or cool (endo)? (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy).

This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? The temperature decrease from 22°C to 14°C upon dissolving shows heat absorption from surroundings, indicating an endothermic process. Choice A correctly classifies the process as endothermic by properly interpreting the cooling as absorption of heat. Distractors like Choice C fail by linking exothermic release to cooling, but release would warm surroundings—remember to match energy direction to temperature effect! The exothermic vs endothermic identification strategy: (1) Look for temperature change observations: Did temperature increase (solution got warmer, beaker hot to touch)? → EXOTHERMIC (reaction released heat to surroundings). Did temperature decrease (solution got colder, beaker cool to touch)? → ENDOTHERMIC (reaction absorbed heat from surroundings). No thermometer? Use your hand—does it feel warm (exo) or cool (endo)? (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy). (3) Check examples: combustion/burning (exo), photosynthesis (endo), ice melting (endo), hand warmers (exo), cold packs (endo), respiration (exo). Recognizing common examples helps! Memory tricks: EXOthermic = EXITs energy = energy comes OUT (releases to surroundings). ENDOthermic = energy goes IN = reaction absorbs energy (takes IN from surroundings). Or: EXOthermic = external gets hot (surroundings warm up). ENDOthermic = internal needs heat (reaction needs energy absorbed). Temperature thinking: the SURROUNDINGS' temperature change tells you the direction! If you touch the beaker and it's hot, the reaction GAVE heat to the beaker (exothermic). If the beaker is cold, the reaction TOOK heat from the beaker (endothermic). You're measuring the surroundings, which tells you what the reaction did: released (exo) or absorbed (endo) energy! Fantastic progress—stay curious!

This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? In Beaker 1, the temperature rise to 30°C shows exothermic with energy from system to surroundings; in Beaker 2, the drop to 16°C shows endothermic with energy from surroundings to system. Choice B correctly classifies the reaction as exothermic by properly interpreting the energy transfer direction from observable evidence for both beakers. Choice A fails by swapping the classifications, reversing the energy flow based on temperature changes. The exothermic vs endothermic identification strategy: (1) Look for temperature change observations: Did temperature increase (solution got warmer, beaker hot to touch)? → EXOTHERMIC (reaction released heat to surroundings). Did temperature decrease (solution got colder, beaker cool to touch)? → ENDOTHERMIC (reaction absorbed heat from surroundings). No thermometer? Use your hand—does it feel warm (exo) or cool (endo)? (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy). (3) Check examples: combustion/burning (exo), photosynthesis (endo), ice melting (endo), hand warmers (exo), cold packs (endo), respiration (exo). Recognizing common examples helps! Memory tricks: EXOthermic = EXITs energy = energy comes OUT (releases to surroundings). ENDOthermic = energy goes IN = reaction absorbs energy (takes IN from surroundings). Or: EXOthermic = external gets hot (surroundings warm up). ENDOthermic = internal needs heat (reaction needs energy absorbed). Temperature thinking: the SURROUNDINGS' temperature change tells you the direction! If you touch the beaker and it's hot, the reaction GAVE heat to the beaker (exothermic). If the beaker is cold, the reaction TOOK heat from the beaker (endothermic). You're measuring the surroundings, which tells you what the reaction did: released (exo) or absorbed (endo) energy! Fantastic comparing multiple setups!

This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? Reaction X only proceeds while being heated and stops when heat is removed—this shows the reaction continuously absorbs energy from the burner (surroundings) to proceed. This is endothermic behavior: the reaction needs constant energy input because it's absorbing that energy. Choice A correctly identifies this as endothermic because the reaction absorbs energy from surroundings to proceed. Choice C incorrectly claims needing heat proves the reaction releases heat—that's backwards! If it released heat, it wouldn't need continuous heating. The exothermic vs endothermic identification strategy: (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy). Memory tricks: ENDOthermic = energy goes IN = reaction absorbs energy (takes IN from surroundings). If you must keep adding heat for the reaction to continue, that heat is being absorbed BY the reaction—classic endothermic!

This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? The temperature drop from 23°C to 17°C and cooler beaker when dissolving ammonium chloride show heat absorption from the surroundings, indicating an endothermic process with energy flowing from surroundings to system. Choice B correctly classifies the reaction as endothermic by properly interpreting the energy transfer direction from observable evidence like the cooling. Choice A fails by labeling it exothermic, incorrectly tying release to cooling. The exothermic vs endothermic identification strategy: (1) Look for temperature change observations: Did temperature increase (solution got warmer, beaker hot to touch)? → EXOTHERMIC (reaction released heat to surroundings). Did temperature decrease (solution got colder, beaker cool to touch)? → ENDOTHERMIC (reaction absorbed heat from surroundings). No thermometer? Use your hand—does it feel warm (exo) or cool (endo)? (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy). (3) Check examples: combustion/burning (exo), photosynthesis (endo), ice melting (endo), hand warmers (exo), cold packs (endo), respiration (exo). Recognizing common examples helps! Memory tricks: EXOthermic = EXITs energy = energy comes OUT (releases to surroundings). ENDOthermic = energy goes IN = reaction absorbs energy (takes IN from surroundings). Or: EXOthermic = external gets hot (surroundings warm up). ENDOthermic = internal needs heat (reaction needs energy absorbed). Temperature thinking: the SURROUNDINGS' temperature change tells you the direction! If you touch the beaker and it's hot, the reaction GAVE heat to the beaker (exothermic). If the beaker is cold, the reaction TOOK heat from the beaker (endothermic). You're measuring the surroundings, which tells you what the reaction did: released (exo) or absorbed (endo) energy! Excellent work on dissolution examples!

This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? Here, the temperature drop from 24°C to 10°C and the cold feel show the chemical mixing absorbed heat from the surroundings, making this an endothermic process with energy flowing from surroundings to the system. Choice B correctly classifies the reaction as endothermic by properly interpreting the energy transfer direction from observable evidence like the cooling effect. Choice A fails by misclassifying it as exothermic, incorrectly linking heat release to cooling. The exothermic vs endothermic identification strategy: (1) Look for temperature change observations: Did temperature increase (solution got warmer, beaker hot to touch)? → EXOTHERMIC (reaction released heat to surroundings). Did temperature decrease (solution got colder, beaker cool to touch)? → ENDOTHERMIC (reaction absorbed heat from surroundings). No thermometer? Use your hand—does it feel warm (exo) or cool (endo)? (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy). (3) Check examples: combustion/burning (exo), photosynthesis (endo), ice melting (endo), hand warmers (exo), cold packs (endo), respiration (exo). Recognizing common examples helps! Memory tricks: EXOthermic = EXITs energy = energy comes OUT (releases to surroundings). ENDOthermic = energy goes IN = reaction absorbs energy (takes IN from surroundings). Or: EXOthermic = external gets hot (surroundings warm up). ENDOthermic = internal needs heat (reaction needs energy absorbed). Temperature thinking: the SURROUNDINGS' temperature change tells you the direction! If you touch the beaker and it's hot, the reaction GAVE heat to the beaker (exothermic). If the beaker is cold, the reaction TOOK heat from the beaker (endothermic). You're measuring the surroundings, which tells you what the reaction did: released (exo) or absorbed (endo) energy! You're doing great—keep connecting observations to energy flow!

This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? The need for continuous heating to sustain the decomposition of calcium carbonate indicates it absorbs energy from the heat source, classifying it as endothermic. Choice B correctly classifies the reaction as endothermic by properly interpreting the energy transfer direction from the requirement for ongoing input. Choice A fails by calling it exothermic, misunderstanding that energy input points to absorption. The exothermic vs endothermic identification strategy: (1) Look for temperature change observations: Did temperature increase (solution got warmer, beaker hot to touch)? → EXOTHERMIC (reaction released heat to surroundings). Did temperature decrease (solution got colder, beaker cool to touch)? → ENDOTHERMIC (reaction absorbed heat from surroundings). No thermometer? Use your hand—does it feel warm (exo) or cool (endo)? (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy). (3) Check examples: combustion/burning (exo), photosynthesis (endo), ice melting (endo), hand warmers (exo), cold packs (endo), respiration (exo). Recognizing common examples helps! Memory tricks: EXOthermic = EXITs energy = energy comes OUT (releases to surroundings). ENDOthermic = energy goes IN = reaction absorbs energy (takes IN from surroundings). Or: EXOthermic = external gets hot (surroundings warm up). ENDOthermic = internal needs heat (reaction needs energy absorbed). Temperature thinking: the SURROUNDINGS' temperature change tells you the direction! If you touch the beaker and it's hot, the reaction GAVE heat to the beaker (exothermic). If the beaker is cold, the reaction TOOK heat from the beaker (endothermic). You're measuring the surroundings, which tells you what the reaction did: released (exo) or absorbed (endo) energy! You're getting the hang of energy input clues—keep it up!

This question tests your understanding of exothermic reactions (which release energy to surroundings, making them feel hot) and endothermic reactions (which absorb energy from surroundings, making them feel cold). Exothermic and endothermic reactions differ in energy flow direction: EXOTHERMIC reactions release energy—usually as heat—to the surroundings, causing the temperature of the surroundings to increase (the reaction mixture or container feels hot, thermometer reading goes up). Examples include combustion (burning releases heat), hand warmers (iron oxidation releases heat), and acid-base neutralization (mixing acid and base releases heat, warming the solution). ENDOTHERMIC reactions absorb energy from the surroundings, causing the temperature of the surroundings to decrease (reaction mixture feels cold, thermometer reading goes down). Examples include instant cold packs (ammonium nitrate dissolving absorbs heat, cooling the pack), photosynthesis (plants absorb light energy to make glucose), and ice melting (absorbs heat from surroundings, cooling your drink). The key: look at what happens to the surroundings—do they get hotter (exothermic) or colder (endothermic)? The slow temperature rise from 25°C to 28°C during yeast fermentation, along with gas production, indicates the process released energy to the surroundings, making it exothermic. Choice A correctly classifies the reaction as exothermic by properly interpreting the energy transfer direction from observable evidence like the warming. Choice B fails by calling it endothermic, wrongly linking absorption to a temperature increase. The exothermic vs endothermic identification strategy: (1) Look for temperature change observations: Did temperature increase (solution got warmer, beaker hot to touch)? → EXOTHERMIC (reaction released heat to surroundings). Did temperature decrease (solution got colder, beaker cool to touch)? → ENDOTHERMIC (reaction absorbed heat from surroundings). No thermometer? Use your hand—does it feel warm (exo) or cool (endo)? (2) Look for energy input requirements: Does reaction need continuous heating, light, or electricity to proceed? → likely ENDOTHERMIC (absorbing that energy). Does reaction proceed on its own, producing heat or light? → likely EXOTHERMIC (releasing energy). (3) Check examples: combustion/burning (exo), photosynthesis (endo), ice melting (endo), hand warmers (exo), cold packs (endo), respiration (exo). Recognizing common examples helps! Memory tricks: EXOthermic = EXITs energy = energy comes OUT (releases to surroundings). ENDOthermic = energy goes IN = reaction absorbs energy (takes IN from surroundings). Or: EXOthermic = external gets hot (surroundings warm up). ENDOthermic = internal needs heat (reaction needs energy absorbed). Temperature thinking: the SURROUNDINGS' temperature change tells you the direction! If you touch the beaker and it's hot, the reaction GAVE heat to the beaker (exothermic). If the beaker is cold, the reaction TOOK heat from the beaker (endothermic). You're measuring the surroundings, which tells you what the reaction did: released (exo) or absorbed (endo) energy! Fermentation heats things up—nice catch!