Question

What sequence of coefficients will balance the following equation? `Ca(s) + O_2(g) -> 2CaO(s)`

Answer 1

You place a 2 in front of the `Ca` on the left side of the arrow to make the reaction balanced.

Explanation:

A reaction needs to be balanced in order to fulfil the Law of conservation of mass. Therefore at both sides of the reaction arrow (`->`) we must have the same amount of each atom. The act of doing so is called balancing.

Your reaction is
`Ca+O_2->2 CaO`

The first step to do, is to look how many atoms are on both sides of the arrow.

left side
`1xxCa`
`2xxO` (in `O_2`, there are `2xx O` atoms)

right side
`2xxCa`
`2xxO`

To balance the reaction, we must have on the left side 2 `Ca`-atoms. Therefore we place a 2 in front of the `Ca` on the left side. We obtain:
`2Ca+O_2->2 CaO`

You can see, that we now have 2 atoms of each element at the left and right side of the arrow. Therefore the reaction is balanced!

`color(red)("Please keep in mind:")`
By balancing reactions, you should only set the numbers in front of the molecules (like 2 Ca),
and thus not change the molecules (like `Ca_2` which is a different molecule)
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