What happens when (give balanced equations):
A mixture of ethene and hydrogen is passed over nickel at `159^@C`

Explanation

To solve the question, we need to understand what happens when a mixture of ethene (C₂H₄) and hydrogen (H₂) is passed over nickel (Ni) at a temperature of 159°C. The process involved is known as hydrogenation.

### Step-by-Step Solution:

1. **Identify the Reactants**:
- Ethene (C₂H₄)
- Hydrogen (H₂)

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