Question

Alkanes undergo combustion in the presence of oxygen. Consider the following combustion reaction of an alkane, where a is an unknown co-efficient:
a CnH2n + 2 (g) + 7O2(g) à 4CO2(g) + 6H2O(g)

The alkane is
Question 9 options:

methane

ethane

propane

butane

pentane

Answer 1

Ethane.

Reason: From the products, total C = 4 so a·n = 4, and total H = 12 (from 6 H2O) so a·(2n+2) = 12. Solving gives a = 2 and n = 2, so the alkane is C2H6 (ethane). The balanced equation is 2C2H6 + 7O2 → 4CO2 + 6H2O.