Calculator Input
Example Data Table
| Case | Mass (g) | Cp (J/g·°C) | Ti (°C) | Tf (°C) | Ccal (J/°C) | Effective Moles | Reaction Heat (kJ) | ΔH (kJ/mol) |
|---|---|---|---|---|---|---|---|---|
| Ammonium nitrate dissolution | 250 | 4.18 | 25.0 | 18.5 | 45 | 0.1200 | 7.0850 | 59.0417 |
| Barium hydroxide mixture | 500 | 3.95 | 24.0 | 16.0 | 60 | 0.2000 | 16.2800 | 81.4000 |
| Hydrated salt absorption run | 150 | 4.20 | 27.0 | 21.8 | 30 | 0.0684 | 3.4320 | 50.1754 |
Formula Used
1. Effective mass from direct entry or density correction:
m = entered mass or m = volume × density
2. Effective reacted moles with purity, conversion, and scaling:
neffective = n × (purity / 100) × (conversion / 100) × batches
3. Temperature change:
ΔT = Tfinal - Tinitial
4. Heat exchanged by surroundings:
qsurroundings = (m × c + Ccal) × ΔT
5. Reaction heat from calorimetry sign convention:
qreaction = -qsurroundings
6. Molar enthalpy change:
ΔH = qreaction / neffective
For an endothermic reaction, the measured mixture often cools, giving a negative ΔT and a positive qreaction.
How to Use This Calculator
- Enter the reaction name to label the run.
- Provide solution mass directly, or enter volume and density.
- Add specific heat capacity and the calorimeter constant.
- Type the initial and final measured temperatures.
- Enter reacted moles, then adjust purity, conversion, and batch count.
- Press Calculate Heat to display results above the form.
- Review reaction heat, molar enthalpy, energy conversions, and the Plotly graph.
- Use the CSV and PDF buttons to export the calculation summary.
FAQs
1. What does a positive reaction heat mean here?
A positive reaction heat means the reaction absorbed energy. In calorimetry, that usually happens when the solution temperature drops, so the surroundings lose heat while the reaction gains it.
2. Why is the sign opposite between surroundings heat and reaction heat?
Energy conservation requires the reaction and surroundings to balance. When the surroundings cool and carry a negative heat value, the reaction receives that energy and becomes positive.
3. Can I use volume instead of mass?
Yes. Leave direct mass empty and enter solution volume with density. The calculator multiplies them to estimate mass before computing total heat capacity and reaction heat.
4. What specific heat value should I enter?
Use the measured or literature specific heat for the reaction mixture. If unavailable, many dilute aqueous systems are approximated near 4.18 J/g·°C, but measured values are better.
5. Why do purity and conversion matter?
They adjust reacted moles to match real chemical participation. Lower purity or incomplete conversion reduces the effective amount reacting, which changes the calculated molar enthalpy.
6. What if my result becomes negative?
A negative reaction heat means the entered temperatures describe an exothermic signature. Double-check the sign, probe readings, mixing time, and whether the process is actually endothermic.
7. Does the calorimeter constant always matter?
It matters whenever the container, probe, lid, or sensor stores measurable heat. Ignoring a nontrivial calorimeter constant can understate or overstate reaction heat, especially in small samples.
8. What does the graph show?
The graph shows how calculated reaction heat changes along the temperature path from the initial reading to the final reading. It helps visualize the thermal direction and total absorbed energy.