# Question #1e358

Jan 15, 2017

${\text{CaC"_2 + "2H"_2"O" → "C"_2"H"_2 + "Ca(OH)}}_{2}$

#### Explanation:

You follow a systematic procedure to balance the equation.

The other product is calcium hydroxide.

Start by converting the words to a chemical equation.:

${\text{CaC"_2 + "H"_2"O" → "C"_2"H"_2 + "Ca(OH)}}_{2}$

A method that often works is first to balance everything other than $\text{O}$ and $\text{H}$, then balance $\text{O}$, and finally balance $\text{H}$.

Another useful procedure is to start with what looks like the most complicated formula.

The most complicated formula looks like ${\text{Ca(OH)}}_{2}$. We put a 1 in front of it to remind ourselves that the number is now fixed.

${\text{CaC"_2 + "H"_2"O" → "C"_2"H"_2 + color(red)(1)"Ca(OH)}}_{2}$

Balance $\text{Ca}$:

We have $\text{1 Ca}$ on the right, so we need $\text{1 Ca}$ on the left. We put a 1 in front of the ${\text{CaC}}_{2}$.

$\textcolor{\mathmr{and} a n \ge}{1} {\text{CaC"_2 + "H"_2"O" → "C"_2"H"_2 + color(red)(1)"Ca(OH)}}_{2}$

Balance $\text{C}$:

We have fixed $\text{2 C}$ on the left. We need $\text{2 C}$ on the right. Put a 1 in front of ${\text{C"_2"H}}_{2}$.

$\textcolor{\mathmr{and} a n \ge}{1} {\text{CaC"_2 + "H"_2"O" → color(blue)(1)"C"_2"H"_2 + color(red)(1)"Ca(OH)}}_{2}$

Balance $\text{O}$:

We have fixed $\text{2 O}$ on the right. We need $\text{2 O}$ on the left. Put a 2 in front of $\text{H"_2"O}$.

$\textcolor{\mathmr{and} a n \ge}{1} {\text{CaC"_2 + color(purple)(2)"H"_2"O" → color(blue)(1)"C"_2"H"_2 + color(red)(1)"Ca(OH)}}_{2}$

Every formula now has a coefficient. We should have a balanced equation.

Let's check.

$\boldsymbol{\text{Atom" color(white)(m)"lhs"color(white)(m)"rhs}}$
$\textcolor{w h i t e}{m} \text{Ca} \textcolor{w h i t e}{m m l} 1 \textcolor{w h i t e}{m m l} 1$
$\textcolor{w h i t e}{m} \text{C} \textcolor{w h i t e}{m m m} 2 \textcolor{w h i t e}{m m l} 2$
$\textcolor{w h i t e}{m} \text{H} \textcolor{w h i t e}{m m m} 4 \textcolor{w h i t e}{m m l} 4$
$\textcolor{w h i t e}{m} \text{O} \textcolor{w h i t e}{m m m} 2 \textcolor{w h i t e}{m m l} 2$

All atoms balance. The balanced equation is

${\text{CaC"_2 + "2H"_2"O" → "C"_2"H"_2 + "Ca(OH)}}_{2}$