Molar MassMolar mass of ethane (C2H6)
The molar mass of ethane, C2H6, is 30.07 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 30.07 grams.
About ethane
Ethane is the second member of the alkane family and is present in natural gas. It is cracked to make ethene for plastics.
The working
The formula C2H6 has 2 carbon atoms and 6 hydrogen atoms, 8 atoms in all. Multiply each count by the atomic weight of the element and add:
| Element | Atoms | Atomic weight | Total | Share by mass |
|---|---|---|---|---|
| Carbon (C) | 2 | 12.011 | 24.022 | 79.89% |
| Hydrogen (H) | 6 | 1.0080 | 6.048 | 20.11% |
2 × 12.011 + 6 × 1.0080 = 30.070 g/mol
With the rounded atomic masses used in many school books (C = 12, H = 1) the answer is 30 g/mol. The difference from 30.07 is too small to matter in most school sums.
Percentage composition
By mass, C2H6 is 79.89% carbon and 20.11% hydrogen. The largest share comes from carbon. In a 100 g sample there are 79.9 g of carbon and 20.1 g of hydrogen.
Notice that hydrogen has more atoms in the formula (6) than carbon (2), yet gives a smaller share of the mass. Percentage by mass depends on how heavy each atom is, not only on how many there are.
Worked examples
Grams to moles. How many moles are in 20 g of C2H6? Divide the mass by the molar mass: 20 ÷ 30.07 = 0.6651 mol.
Moles to grams. What is the mass of 0.5 mol of C2H6? Multiply: 0.5 × 30.07 = 15.04 g.
Counting particles. 20 g contains 0.6651 mol × 6.022 × 1023 = 4.005 × 1023 molecules, and 3.204 × 1024 atoms in all.
As a gas. At 0 °C and 1 atmosphere one mole of an ideal gas occupies 22.4 litres, so the density of C2H6 is about 30.07 ÷ 22.4 = 1.34 g per litre. Air averages about 29 g/mol, so this gas is heavier than air.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 3.007 g |
| 0.5 mol | 15.04 g |
| 1 mol | 30.07 g |
| 2 mol | 60.14 g |
| 5 mol | 150.3 g |
| Mass | Moles |
|---|---|
| 1 g | 0.03326 mol |
| 10 g | 0.3326 mol |
| 100 g | 3.326 mol |
| 1 kg | 33.26 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of C2H6?
The molar mass of ethane (C2H6) is 30.07 g/mol, or 30.070 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of C2H6?
100 ÷ 30.07 = 3.326 mol.
What is the mass of one molecule of C2H6?
Divide the molar mass by the Avogadro constant: 30.07 ÷ 6.022 × 1023 = 4.993 × 10-23 g.
What is the percentage of carbon in C2H6?
Carbon makes up 79.89% of the mass of C2H6: 2 × 12.011 ÷ 30.070 × 100.
Which values? This site uses the abridged standard atomic weights published by IUPAC (CIAAW), read on 12 November 2026. Your textbook or question paper may round them differently, for example H = 1 and O = 16, so its answer can differ slightly. In an exam, use the values the paper gives.