Topic 2 of 4
Investigate an energy change
Make the measurement large enough to interpret fairly.
O-Level 6092 (2026) / SEC G3 K324 (2027)
Investigate an energy change
Make the measurement large enough to interpret fairly.
Measure the initial temperatures, mix the specified quantities in an insulated cup, stir consistently and record the highest or lowest temperature reached. A lid reduces energy transfer to the air; the probe should measure the mixture rather than rest on the cup. Use the same volumes, concentrations and apparatus when comparing repeats.
Worked example
Interpret a cooling experiment
Water starts at 24 degrees C. After a salt dissolves, the lowest temperature is 18 degrees C, before slowly returning towards 24.
- The initial fall is evidence that the dissolving process absorbed energy.
- The change in the measured temperature is 18 - 24 = -6 degrees C.
- The later warming occurs as the cooler solution gains energy from the room.
Dissolving is endothermic. The later return towards room temperature does not change that classification.
A smaller observed temperature change may result from heat exchange with the room, a different amount of reacting substance or a different amount of water being warmed. It need not mean a different reaction type. Report measurements and limitations rather than claiming that temperature change alone is an energy value in joules.