What is the formation (not combustion) equation of C2H4 gas?

Ethene or ethylene (C2H4) is formed by catalytic dehydration of ethyl alcohol (or ethanol). The relevant equation can be written as:

`C_2H_5OH (g) -> C_2H_4 (g) + H_2O (g)`

The catalyst for this reaction can be concentrated sulfuric acid (H2SO4) or concentrated phosphoric acid (H3PO4). We can also use pumice powder or aluminum oxide (Al2O3) powder.

For this reaction, ethanol is heated till it vaporizes and these vapors are passed over the heated catalyst. These heated ethanol vapors undergo cracking and result in ethene gas and water vapors.

In a laboratory setup, we can collect all the resulting ethene gas in inverted glass tubes, kept in a vessel full of water (to avoid air contact).

If you are using concentrated acids for catalysis, just make sure to be very cautious for safety reasons.

Hope this helps.