Chapter 9, Problem 11STP

Interpretation Introduction

Interpretation:

The balanced chemical equation for the reaction of solid calcium with water to produce calcium hydroxide and hydrogen gas needs to be determined.

Concept introduction:

For balancing an equation first write the skeleton equation. After that count the atoms of both side, count each polyatomic ion as a single element. Find the correct coefficient and placed them in front of the atoms and checked both side element equal or not.

Answer to Problem 11STP

The balanced equation is as follows:

$\text{Ca}\left(\text{s}\right){\text{+2H}}_2\text{O}\left(\text{l}\right)\to \text{Ca}{\left(\text{OH}\right)}_{\text{2}}\left(\text{aq}\right){\text{+H}}_2\left(\text{g}\right)$

Explanation of Solution

Write the word equation for the reaction of solid calcium with water to produce calcium hydroxide and hydrogen gas.

$\text{Calcium}\left(\text{s}\right)\text{+water}\left(\text{l}\right)\to \text{Calcium}\text{hydroxide}\left(\text{aq}\right)\text{+Hydrogen}\left(\text{g}\right)$

Now, write the skeleton equations.

$\text{Ca}\left(\text{s}\right){\text{+H}}_2\text{O}\left(\text{l}\right)\to \text{Ca}{\left(\text{OH}\right)}_{\text{2}}\left(\text{aq}\right){\text{+H}}_2\left(\text{g}\right)$

In the reactant side number of calcium is 1, hydrogen is 2 and oxygen atom is 1 while in product side number of calcium is 1, oxygen is two and hydrogen is 4. To balance H and O in both sides multiply the reactant side water molecule by 2. Therefore, the equation become

$\text{Ca}\left(\text{s}\right){\text{+2H}}_2\text{O}\left(\text{l}\right)\to \text{Ca}{\left(\text{OH}\right)}_{\text{2}}\left(\text{aq}\right){\text{+H}}_2\left(\text{g}\right)$

Conclusion

A balanced chemical equation means the number of atoms on both the product side participates and the reactant side is identical.