Question

h3po4 + hcl → pcl5 + h2o

Explanation:

Step1: Balance phosphorus

$$\text{H}_3\text{PO}_4 + \text{HCl} ightarrow \text{PCl}_5 + \text{H}_2\text{O}$$

There is 1 P on both sides.

Step2: Balance oxygen

$$\text{H}_3\text{PO}_4 + \text{HCl} ightarrow \text{PCl}_5 + 4\text{H}_2\text{O}$$

Left side has 4 O (from $\text{H}_3\text{PO}_4$), right side now has 4 O (from $4\text{H}_2\text{O}$).

Step3: Balance hydrogen

$$\text{H}_3\text{PO}_4 + 5\text{HCl} ightarrow \text{PCl}_5 + 4\text{H}_2\text{O}$$

Left side has $3 + 5 = 8$ H (from $\text{H}_3\text{PO}_4$ and $5\text{HCl}$), right side has $4\times2 = 8$ H (from $4\text{H}_2\text{O}$).

Step4: Balance chlorine

$$\text{H}_3\text{PO}_4 + 5\text{HCl} ightarrow \text{PCl}_5 + 4\text{H}_2\text{O}$$

Left side has 5 Cl (from $5\text{HCl}$), right side has 5 Cl (from $\text{PCl}_5$).

Answer:

$$\text{H}_3\text{PO}_4 + 5\text{HCl} ightarrow \text{PCl}_5 + 4\text{H}_2\text{O}$$