Question

What is the sum of the coefficients of the products for the following reaction?
$K_{2}C{r}_2{O}_7+HCl\to KCl+CrC{l}_3+H_{2}O+C{l}_2$

• A. 10
• B. 12
• C. 13
• D. 14
• E. 15

Answer 1

The correct option is D 14

The unbalanced chemical equation is
$K_{2}C{r}_2{O}_7+HCl\to KCl+CrC{l}_3+H_{2}O+C{l}_2$
Balance all atoms except H and O.
$K_{2}C{r}_2{O}_7+10HCl\to 2KCl+2CrC{l}_3+H_{2}O+C{l}_2$
Assign oxidation numbers.

$K_2\underset{+6}{C{r}_2}{O}_7+10H\underset{-1}{Cl}\to 2KCl+2\underset{+3}{Cr}C{l}_3+H_{2}O+\underset{0}{C{l}_2}$
The oxidation number of Cr decreases from +6 to +3. Total decrease in the oxidation number of two Cr atoms is 6. The oxidation number of Cl increases from -1 to 0. Total increase in the oxidation number of 2 Cl atoms is 2.
Balance increase in oxidation number with decrease in oxidation number by using appropriate coefficients.
$K_{2}C{r}_2{O}_7+14HCl\to 2KCl+2CrC{l}_3+H_{2}O+3C{l}_2$
Balance O atoms by adding six water molecules on products side.
$K_{2}C{r}_2{O}_7+14HCl\to 2KCl+2CrC{l}_3+7H_{2}O+3C{l}_2$
H atoms are balanced.
$K_{2}C{r}_2{O}_7+14HCl\to 2KCl+2CrC{l}_3+7H_{2}O+3C{l}_2$
This is balanced chemical equation.
The sum of the coefficients of the products is $2+2+7+3=14$