Question

When the equation `C_2H_4+O_2 -> CO_2+H_2O` is balanced using smallest whole numbers, what is the coefficient of the `O_2`?

Answer 1

`C_2H_4(g) + 3O_2(g) rarr 2CO_2(g) + 2H_2O(l)`

Explanation:

The answer is `3`. Is this balanced? For every reactant particle, is there a corresponding product particle? There are `2C` reactant particles, and `2C` product particles. You have to count up the number of remaining hydrogen and oxygen reactant particles, and see if these correspond to the number of hydrogen and oxygen product particles.

If these numbers do not agree, you know that the reaction is unbalanced; therefore, it is not consistent with physical reality.