kJ/mol to J Converter
Chemistry books list energy in kJ/mol, and sometimes you need J/mol or J per molecule. The first is times 1,000. The second needs one more divide.
Quick answer: multiply the kJ/mol by 1,000 to get J/mol. For example, 1 kJ/mol is 1,000 J/mol, 40.65 kJ/mol is 40,650 J/mol and 100 kJ/mol is 100,000 J/mol.
The kJ/mol to J formula
A kilojoule is 1,000 joules (Wikipedia: Joule per mole).
So you multiply the kJ/mol by 1,000 to get J/mol.
Take 40.65 kJ/mol. Multiply by 1,000. The answer is 40,650 J/mol.
Take 100 kJ/mol. Multiply by 1,000. The answer is 100,000 J/mol.
Energy per mole
The J/mol is the SI unit of molar energy. The kJ/mol is 1,000 times bigger (Wikipedia: Joule per mole).
Chemists use kJ/mol because J/mol numbers are too long (Wikipedia: Joule per mole).
To get energy per molecule, divide by the Avogadro constant, 6.022 × 10²³ per mole.
How to convert kJ/mol to J step by step
- Write down the energy in kJ/mol.
- Multiply by 1,000.
- The answer is in J/mol.
- Divide by 6.022 × 10²³ for J per molecule.
Example 1: 40.65 kJ/mol
- Water takes about 40.65 kJ to vaporize one mole.
- 40.65 × 1,000 = 40,650.
- The energy is 40,650 J/mol.
40.65 kJ/mol = 40,650 J/mol
Example 2: 100 kJ/mol
- A typical bond is about 100 kJ/mol (Wikipedia: Joule per mole).
- 100 × 1,000 = 100,000.
- The energy is 100,000 J/mol.
100 kJ/mol = 100,000 J/mol
Example 3: 1 kJ/mol per molecule
- Start with 1 kJ/mol, which is 1,000 J/mol.
- 1,000 ÷ 6.022 × 10²³ = 1.66 × 10⁻²¹.
- That is 1.66 × 10⁻²¹ J per molecule.
1 kJ/mol = 1.66 × 10⁻²¹ J per molecule
Ionization energies are about 1,000 kJ/mol, which is 1,000,000 J/mol (Wikipedia: Joule per mole).
kJ/mol to J conversion table
| kJ/mol | J/mol | J per molecule |
|---|---|---|
| 1 kJ/mol | 1,000 J/mol | 1.6605e-21 J per molecule |
| 10 kJ/mol | 10,000 J/mol | 1.6605e-20 J per molecule |
| 40.65 kJ/mol | 40,650 J/mol | 6.7501e-20 J per molecule |
| 100 kJ/mol | 100,000 J/mol | 1.6605e-19 J per molecule |
| 242 kJ/mol | 242,000 J/mol | 4.0185e-19 J per molecule |
| 413 kJ/mol | 413,000 J/mol | 6.8580e-19 J per molecule |
| 436 kJ/mol | 436,000 J/mol | 7.2400e-19 J per molecule |
| 1,000 kJ/mol | 1,000,000 J/mol | 1.6605e-18 J per molecule |
The highlighted row, 40.65 kJ/mol, is the default of the converter. The last column divides by the Avogadro constant.
A quick mental shortcut for kJ/mol to J
Move the decimal three places right. So 2.5 kJ/mol is 2,500 J/mol.
The name changes, but the energy is the same.
What a kJ/mol is
It is 1,000 joules for each mole of a substance (Wikipedia: Joule per mole).
It is common in enthalpy and bond tables.
What a J/mol is
It is the SI unit of molar energy (Wikipedia: Joule per mole).
Its base form is kg·m²·s⁻²·mol⁻¹.
Typical values
Heats of fusion and vaporization are about 10 kJ/mol. Bond energies are about 100 kJ/mol (Wikipedia: Joule per mole).
Ionization energies are about 1,000 kJ/mol.
Per mole or per molecule
Per mole means 6.022 × 10²³ particles. Per molecule means just one.
Always check which one a table gives.
Gibbs and enthalpy
Free energy and enthalpy are often written in kJ/mol (Wikipedia: Joule per mole).
Use J/mol when the calculation needs SI units.
Gas constant sums
The gas constant R is 8.314 J/(mol·K). So an energy used with R must be in J/mol.
That is the main reason to change kJ/mol to J/mol.
Other molar units
Divide kJ/mol by 4.184 to get kcal/mol (Wikipedia: Kilocalorie per mole). Divide by 96.485 to get eV per particle.
Use the linked converters.
J/mol back to kJ/mol
To go back, divide the J/mol by 1,000.
So 40,650 J/mol is 40.65 kJ/mol.
Check your answer
Divide your J/mol answer by 1,000. You should get your starting kJ/mol.
The J/mol number must be 1,000 times bigger.
More values at a glance
0.1 kJ/mol is 100 J/mol, 1 kJ/mol is 1,000 J/mol and 5 kJ/mol is 5,000 J/mol.
10 kJ/mol is 10,000 J/mol, 50 kJ/mol is 50,000 J/mol and 100 kJ/mol is 100,000 J/mol.
500 kJ/mol is 500,000 J/mol, and 1,000 kJ/mol is 1,000,000 J/mol.
The unit sizes
One kJ is 1,000 J. So the J/mol number is always 1,000 times bigger.
If a result looks very large or very small, compare it with these sizes before you use it.
Checking in reverse
Convert 5,000 J/mol back to kJ/mol. You should get 5 kJ/mol.
Energy per molecule
A bond of 400 kJ/mol is 400,000 J/mol. Divide by Avogadro number, 6.022 × 10²³, to get about 6.64 × 10⁻¹⁹ J for one molecule.
Scale of the units
A kJ/mol value is large because it covers a whole mole. One molecule holds a very small share, so state clearly whether your answer is per mole or per particle.
Quick conversion answers
| Conversion | Result |
|---|---|
| 1 kJ/mol to J/mol | 1,000 J/mol |
| 10 kJ/mol to J/mol | 10,000 J/mol |
| 40.65 kJ/mol to J/mol | 40,650 J/mol |
| 100 kJ/mol to J/mol | 100,000 J/mol |
| 436 kJ/mol to J/mol | 436,000 J/mol |
| 1,000 kJ/mol to J/mol | 1,000,000 J/mol |
Where this conversion is used
Chemistry students prepare values for gas-constant sums.
Lab workers move between table and equation units.
Teachers check enthalpy and bond energy answers.
Common mistakes to avoid
- Dividing by 1,000. That goes the wrong way.
- Mixing J/mol and J per molecule. They differ by 6.022 × 10²³.
- Forgetting the unit. J/mol, not J.
- Mixing kJ and kcal. They differ by 4.184.
Related converters
A water example
Water needs 40.65 kJ per mole to vaporize. That is 40,650 J/mol.
Per molecule, it is 6.75 × 10⁻²⁰ J.
A gas constant example
To find a rate with R = 8.314 J/(mol·K), use J/mol. So 50 kJ/mol must become 50,000 J/mol.
Then the sum divides by R times the temperature.
A bond example
The H–H bond is about 436 kJ/mol. That is 436,000 J/mol.
Per molecule, it is 7.24 × 10⁻¹⁹ J.
Frequently asked questions
How do I convert kJ/mol to J/mol?
Multiply the kJ/mol by 1,000.
How many J/mol is 1 kJ/mol?
1,000 J/mol.
How do I get J per molecule?
Divide the J/mol by 6.022 × 10²³.
Why is kJ/mol used?
J/mol numbers are too long.
What is 100 kJ/mol in J/mol?
100,000 J/mol.
How many kcal/mol is 1 kJ/mol?
About 0.239 kcal/mol.
Sources
- Wikipedia: Joule per mole (en.wikipedia.org)
- Wikipedia: Kilocalorie per mole (en.wikipedia.org)
