About this experiment
Explore endothermic and exothermic enthalpy profiles while measuring bulk heating or cooling. Move a reaction-coordinate probe, lower a barrier with a catalyst and independently advance the amount reacted.
Learning goals
- Distinguish reaction enthalpy from forward and reverse activation barriers.
- Verify that a catalyst changes barriers without changing endpoint enthalpies.
- Connect molar enthalpy and reaction extent to calorimeter temperature.
How to use it
- 1Probe the beginning, peak and end of an exothermic enthalpy path.
- 2Follow the catalysed path and compare both activation barriers.
- 3Complete conversion and calculate the heat absorbed by the insulated solution.
- 4Reverse the sign of reaction enthalpy and compare cooling with heating.
The model
Assumptions
- The path is an imposed smooth enthalpy diagram, not a quantum transition-state calculation or a molecular trajectory. Its probe is independent of bulk conversion.
- Conversion is prescribed by the control clock; no rate law, equilibrium conversion or catalyst kinetics is inferred.
- The calorimeter is insulated, starts at 20 °C and has constant solution specific heat 4.18 J per gram kelvin. Reaction volume and solution mass changes are ignored.
Try this in class
- Q1Why does the same reaction heat cause a smaller temperature rise with more solution?
- Q2Why must the reverse barrier change when endpoint enthalpies change?
Frequently asked questions
Can the catalyst change the final calorimeter heat at the same conversion?
No. In this model it changes only the path barrier; endpoint enthalpy and the heat at a specified extent remain unchanged.
Is the moving path bead an individual molecule crossing a real barrier?
No. It is a probe of the displayed schematic energy curve. The model does not assign a probability of barrier crossing.