Molar MassMolar mass of ethene (C2H4)
The molar mass of ethene, C2H4, is 28.05 g/mol. One mole of it, which is 6.022 × 1023 molecules, has a mass of 28.05 grams.
28.05 g/mol
2 × 12.011 + 4 × 1.0080 = 28.054 · 6 atoms in the formula · also called ethylene
About ethene
Ethene is the simplest alkene, with a double bond between its carbon atoms. It is the starting material for polythene and it ripens fruit.
Other names: ethylene.
The working
The formula C2H4 has 2 carbon atoms and 4 hydrogen atoms, 6 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 | 85.63% |
| Hydrogen (H) | 4 | 1.0080 | 4.032 | 14.37% |
2 × 12.011 + 4 × 1.0080 = 28.054 g/mol
With the rounded atomic masses used in many school books (C = 12, H = 1) the answer is 28 g/mol. The difference from 28.05 is too small to matter in most school sums.
Percentage composition
By mass, C2H4 is 85.63% carbon and 14.37% hydrogen. The largest share comes from carbon. In a 100 g sample there are 85.6 g of carbon and 14.4 g of hydrogen.
Notice that hydrogen has more atoms in the formula (4) 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 10 g of C2H4? Divide the mass by the molar mass: 10 ÷ 28.05 = 0.3565 mol.
Moles to grams. What is the mass of 1.5 mol of C2H4? Multiply: 1.5 × 28.05 = 42.08 g.
Counting particles. 10 g contains 0.3565 mol × 6.022 × 1023 = 2.147 × 1023 molecules, and 1.288 × 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 C2H4 is about 28.05 ÷ 22.4 = 1.25 g per litre. Air averages about 29 g/mol, so this gas is lighter than air.
Quick conversion tables
| Amount | Mass |
|---|---|
| 0.1 mol | 2.805 g |
| 0.5 mol | 14.03 g |
| 1 mol | 28.05 g |
| 2 mol | 56.11 g |
| 5 mol | 140.3 g |
| Mass | Moles |
|---|---|
| 1 g | 0.03565 mol |
| 10 g | 0.3565 mol |
| 100 g | 3.565 mol |
| 1 kg | 35.65 mol |
For other amounts use the grams and moles converter.
Questions people ask
What is the molar mass of C2H4?
The molar mass of ethene (C2H4) is 28.05 g/mol, or 28.054 g/mol before rounding, using IUPAC abridged atomic weights.
How many moles are in 100 g of C2H4?
100 ÷ 28.05 = 3.565 mol.
What is the mass of one molecule of C2H4?
Divide the molar mass by the Avogadro constant: 28.05 ÷ 6.022 × 1023 = 4.658 × 10-23 g.
What is the percentage of carbon in C2H4?
Carbon makes up 85.63% of the mass of C2H4: 2 × 12.011 ÷ 28.054 × 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.