Read reaction energy from warming water.
An exothermic reaction transfers energy to the surroundings and has negative ΔH at constant pressure. An endothermic reaction absorbs energy and has positive ΔH. The system and surroundings must be distinguished when assigning signs.
A simple calorimeter estimates solution heat as mcΔT. Reaction heat is its negative when heat loss and apparatus heat capacity are neglected. Divide reaction heat by the reacting amount to obtain molar enthalpy change, keeping J and kJ consistent.
Heat measured by a solution
Explore the relationship
c = 4.18 J g⁻¹ K⁻¹; calorimeter heat capacity and environmental loss neglected. Reaction heat has the opposite sign.
Tap or focus a plotted point to read its values.
View plotted data as a table
| Series | Temperature rise / K | Heat gained by solution / kJ |
|---|---|---|
| Heat gained by solution / kJ | 0 | 0 |
| Heat gained by solution / kJ | 0.25 | 0.1045 |
| Heat gained by solution / kJ | 0.5 | 0.209 |
| Heat gained by solution / kJ | 0.75 | 0.3135 |
| Heat gained by solution / kJ | 1 | 0.418 |
| Heat gained by solution / kJ | 1.25 | 0.5225 |
| Heat gained by solution / kJ | 1.5 | 0.627 |
| Heat gained by solution / kJ | 1.75 | 0.7315 |
| Heat gained by solution / kJ | 2 | 0.836 |
| Heat gained by solution / kJ | 2.25 | 0.9405 |
| Heat gained by solution / kJ | 2.5 | 1.045 |
| Heat gained by solution / kJ | 2.75 | 1.1495 |
| Heat gained by solution / kJ | 3 | 1.254 |
| Heat gained by solution / kJ | 3.25 | 1.3585 |
| Heat gained by solution / kJ | 3.5 | 1.463 |
| Heat gained by solution / kJ | 3.75 | 1.5675 |
| Heat gained by solution / kJ | 4 | 1.672 |
| Heat gained by solution / kJ | 4.25 | 1.7765 |
| Heat gained by solution / kJ | 4.5 | 1.881 |
| Heat gained by solution / kJ | 4.75 | 1.9855 |
| Heat gained by solution / kJ | 5 | 2.09 |
| Heat gained by solution / kJ | 5.25 | 2.1945 |
| Heat gained by solution / kJ | 5.5 | 2.299 |
| Heat gained by solution / kJ | 5.75 | 2.4035 |
| Heat gained by solution / kJ | 6 | 2.508 |
| Heat gained by solution / kJ | 6.25 | 2.6125 |
| Heat gained by solution / kJ | 6.5 | 2.717 |
| Heat gained by solution / kJ | 6.75 | 2.8215 |
| Heat gained by solution / kJ | 7 | 2.926 |
| Heat gained by solution / kJ | 7.25 | 3.0305 |
| Heat gained by solution / kJ | 7.5 | 3.135 |
| Heat gained by solution / kJ | 7.75 | 3.2395 |
| Heat gained by solution / kJ | 8 | 3.344 |
| Heat gained by solution / kJ | 8.25 | 3.4485 |
| Heat gained by solution / kJ | 8.5 | 3.553 |
| Heat gained by solution / kJ | 8.75 | 3.6575 |
| Heat gained by solution / kJ | 9 | 3.762 |
| Heat gained by solution / kJ | 9.25 | 3.8665 |
| Heat gained by solution / kJ | 9.5 | 3.971 |
| Heat gained by solution / kJ | 9.75 | 4.0755 |
| Heat gained by solution / kJ | 10 | 4.18 |
| Heat gained by solution / kJ | 10.25 | 4.2845 |
| Heat gained by solution / kJ | 10.5 | 4.389 |
| Heat gained by solution / kJ | 10.75 | 4.4935 |
| Heat gained by solution / kJ | 11 | 4.598 |
| Heat gained by solution / kJ | 11.25 | 4.7025 |
| Heat gained by solution / kJ | 11.5 | 4.807 |
| Heat gained by solution / kJ | 11.75 | 4.9115 |
| Heat gained by solution / kJ | 12 | 5.016 |
| Heat gained by solution / kJ | 12.25 | 5.1205 |
| Heat gained by solution / kJ | 12.5 | 5.225 |
| Heat gained by solution / kJ | 12.75 | 5.3295 |
| Heat gained by solution / kJ | 13 | 5.434 |
| Heat gained by solution / kJ | 13.25 | 5.5385 |
| Heat gained by solution / kJ | 13.5 | 5.643 |
| Heat gained by solution / kJ | 13.75 | 5.7475 |
| Heat gained by solution / kJ | 14 | 5.852 |
| Heat gained by solution / kJ | 14.25 | 5.9565 |
| Heat gained by solution / kJ | 14.5 | 6.061 |
| Heat gained by solution / kJ | 14.75 | 6.1655 |
| Heat gained by solution / kJ | 15 | 6.27 |
Explore: Compare heat gained for different solution masses at the same temperature rise.
A reaction of 0.050 mol warms 100 g solution by 5.0 K; c = 4.18 J .
- Solution gains 100 × 4.18 × 5.0 = 2090 J.
- ΔH = = −41.8 kJ mol⁻¹.
Assumed knowledge
Mass, temperature change and moles.
Learning checkpoints & source
YOUR LEARNING CHECKPOINT- Distinguish exothermic and endothermic changes.
- Determine molar enthalpy change from calorimetry.