Calculator Inputs
Use the responsive grid below. Large screens show three columns, smaller screens show two, and mobile shows one.
Calculation History
Recent runs are stored during the session for quick comparison.
| Time | Label | Method | Basis | Moles | Heat (kJ) | ΔHm (kJ/mol) | Class |
|---|---|---|---|---|---|---|---|
| No session calculations yet. | |||||||
Example Data Table
| Scenario | Input Summary | Total Heat | Moles | Molar Enthalpy |
|---|---|---|---|---|
| Direct reaction | 48.6 kJ released, 1.20 mol basis | -48.6 kJ | 1.20 mol | -40.5000 kJ/mol |
| Solution calorimetry | 250 g, 4.184 J/g·°C, 24.0→28.6 °C, Ccal=0.09 kJ/°C, 0.10 mol | -5.2256 kJ | 0.10 mol | -52.2560 kJ/mol |
| Phase change | 36 g, 2.26 kJ/g absorbed, 2.00 mol basis | 81.3600 kJ | 2.00 mol | 40.6800 kJ/mol |
Formula Used
Molar enthalpy expresses heat change per mole on a defined basis, such as per mole of limiting reactant, product, or reaction extent.
Direct method: ΔHₘ = q / n
Calorimetry method: q_surroundings = (m × c × ΔT) + (C_cal × ΔT), then ΔHₘ = -q_surroundings / n
Phase-change method: q = m × L, then ΔHₘ = q / n
Use a positive sign when the system absorbs heat and a negative sign when the system releases heat.
How to Use This Calculator
- Enter a sample label and define the mole basis.
- Select the method matching your chemistry data source.
- Choose whether you already know moles or need mass conversion.
- Fill in only the panel used by your selected method.
- Press the calculate button to show the result above the form.
- Review the signed heat, molar enthalpy, and calculation steps.
- Download the current result or the whole session history as CSV or PDF.
FAQs
1. What does molar enthalpy represent?
Molar enthalpy is the heat change linked to one mole of a stated chemical basis. That basis may be a reactant, a product, or one mole of reaction as written.
2. Why is exothermic enthalpy negative?
Exothermic processes release heat from the system to the surroundings. By thermodynamic sign convention, the system loses energy, so the enthalpy change is negative.
3. When should I use the calorimetry method?
Use calorimetry when you measure temperature change in a solution or calorimeter. The calculator converts that observed heat transfer into the reaction enthalpy per mole.
4. Can I enter mass instead of moles?
Yes. Select mass conversion, enter the reacting mass, and supply molar mass in grams per mole. The tool converts mass to moles before calculating molar enthalpy.
5. What basis should I choose for the result?
Choose the basis that matches your report or stoichiometric interpretation. Common choices are per mole of limiting reactant, per mole of product, or per mole of reaction.
6. Why include a calorimeter constant?
The calorimeter itself can absorb heat. Including its constant improves accuracy by adding the heat taken up by the apparatus to the surroundings heat balance.
7. Is phase-change enthalpy different from reaction enthalpy?
Yes. Phase-change enthalpy covers melting, freezing, vaporization, condensation, or similar transitions. Reaction enthalpy describes heat change caused by chemical transformation.
8. What units does this calculator support?
You can work with J, kJ, cal, kcal, mol, mmol, mg, g, and kg. Results are reported as both kJ/mol and J/mol.