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

Jun 13, 2017

You place a 2 in front of the $C a$ 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 ($\to$) we must have the same amount of each atom. The act of doing so is called balancing.

$C a + {O}_{2} \to 2 C a O$

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

left side
$1 \times C a$
$2 \times O$ (in ${O}_{2}$, there are $2 \times O$ atoms)

right side
$2 \times C a$
$2 \times O$

To balance the reaction, we must have on the left side 2 $C a$-atoms. Therefore we place a 2 in front of the $C a$ on the left side. We obtain:
$2 C a + {O}_{2} \to 2 C a O$

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!

$\textcolor{red}{\text{Please keep in mind:}}$
By balancing reactions, you should only set the numbers in front of the molecules (like 2 Ca),
and thus not change the molecules (like $C {a}_{2}$ which is a different molecule)
$\frac{\textcolor{w h i t e}{a a a a a a a a a a a a a a a a}}{\textcolor{w h i t e}{a}}$