A technician burns ethene and ethane separately in the same burner, using the same air supply. Their molecular formulae are shown in the table.
| Fuel | Molecular formula |
|---|---|
| Ethene | C2H4\text{C}_2\text{H}_4C2H4 |
| Ethane | C2H6\text{C}_2\text{H}_6C2H6 |
Explain why ethene is expected to produce a smokier flame than ethane.