Calculator
Result
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Formula:
E_{mass} = \frac{E_{molar}}{M}
Where Emolar is in J/mol, M in g/mol, and Emass in J/g before any output-unit conversion.
Results Table
| # | Energy | Molar mass | Output unit | Result | Timestamp |
|---|
Example data table
| Energy (per mol) | Molar mass | Output | |
|---|---|---|---|
| 50,000 J/mol | 58.44 g/mol | J/g | |
| 285.8 kJ/mol | 18.015 g/mol | kJ/g | |
| 3.5 MJ/mol | 44.01 g/mol | kJ/g |
Formula used
Core relation: energy per gram equals energy per mole divided by molar mass.
E_{mass} \;[J/g] = \dfrac{E_{molar} \;[J/mol]}{M \;[g/mol]}Unit handling:
- Normalize Emolar to J/mol: multiply by 10³ for kJ/mol, by 10⁶ for MJ/mol; multiply by 4.184 for cal/mol, by 4184 for kcal/mol.
- Normalize M to g/mol: multiply by 1000 if entered in kg/mol.
- Compute J/g, then convert to the desired output unit (kJ/g = J/g ÷ 1000; MJ/g = J/g ÷ 10⁶).
How to use this calculator
- Enter the energy per mole value and select its unit.
- Enter the compound’s molar mass and select its unit.
- Choose your preferred output unit, then click Calculate.
- Review the step-by-step normalization and final computed value.
- Click Add to table to accumulate multiple results.
- Use Export CSV or Export PDF to download your table.
One line per entry, comma-separated:
energy, energyUnit, molarMass, massUnit, outUnitExample: 285.8, kJ/mol, 18.015, g/mol, kJ/g
Notes
- All computations are performed client-side in your browser.
- Use appropriate significant figures for scientific reporting.
- Molar mass must be greater than zero.
More about J/mol → J/g
Why convert J/mol to J/g?
- Compare energetic quantities across different substances by mass, not moles.
- Report data aligned with gravimetric specifications in materials datasets.
- Prepare inputs for simulations requiring mass-specific energy parameters.
Worked example with ethanol
Given an energy of 1367 kJ/mol and molar mass 46.07 g/mol:
J/mol normalization:
Compute J/g:
Convert to kJ/g:
1367 kJ/mol → 1,367,000 J/molCompute J/g:
1,367,000 ÷ 46.07 ≈ 29,672 J/gConvert to kJ/g:
29,672 J/g ÷ 1000 ≈ 29.7 kJ/g
Rounded to three significant figures for reporting.
Common pitfalls and tips
- Molar mass basis: Always use g/mol for the formula; convert if needed.
- Mixtures: If using a mixture, ensure the molar mass reflects composition.
- Unit mix-ups: Distinguish enthalpy per mole from specific heat capacity units.
- Significant figures: Match the least precise input for the final report.