Question 6.1: Balancing a Chemical Equation Propane, C3H8, is a colorless,......
Balancing a Chemical Equation
Propane, C_3H_8, is a colorless, odorless gas often used as a heating and cooking fuel in campers and rural homes. Write a balanced equation for the combustion reaction of propane with oxygen to yield carbon dioxide and water.
Follow the four steps described in the text:
Step 1 Write the unbalanced equation using correct chemical formulas for all substances:
\mathrm{C}_3 \mathrm{H}_8+\mathrm{O}_2 \longrightarrow \mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \quad \text { Unbalanced }Step 2 Find coefficients to balance the equation. It’s usually best to begin with the most complex substance—in this case C_3H_8—and to deal with one element at a time. Look at the unbalanced equation, and note that there are 3 carbon atoms on the left side of the equation but only 1 on the right side. If we add a coefficient of 3 to CO_2 on the right, the carbons balance:
\mathrm{C}_3 \mathrm{H}_8+\mathrm{O}_2 \longrightarrow 3 \mathrm{CO}_2+\mathrm{H}_2 \mathrm{O} \text { Balanced for } \mathrm{C}Next, look at the number of hydrogen atoms. There are 8 hydrogens on the left but only 2 (in H_2O) on the right. By adding a coefficient of 4 to the H_2O on the right, the hydrogens balance:
\mathrm{C}_3 \mathrm{H}_8+\mathrm{O}_2 \longrightarrow 3 \mathrm{CO}_2+4 \mathrm{H}_2 \mathrm{O} \text { Balanced for } \mathrm{C} \text { and } \mathrm{H}Finally, look at the number of oxygen atoms. There are 2 on the left but 10 on the right. By adding a coefficient of 5 to the O_2 on the left, the oxygens balance:
\mathrm{C}_3 \mathrm{H}_8+5 \mathrm{O}_2 \longrightarrow 3 \mathrm{CO}_2+4 \mathrm{H}_2 \mathrm{O} \text { Balanced for } \mathrm{C}, \mathrm{H} \text {, and } \mathrm{O}Step 3 Make sure the coefficients are reduced to their smallest whole-number values. In this case, our answer is already correct, but we might have arrived at a different answer through trial and error:
2 \mathrm{C}_3 \mathrm{H}_8+10 \mathrm{O}_2 \longrightarrow 6 \mathrm{CO}_2+8 \mathrm{H}_2 \mathrm{O}Although the preceding equation is balanced, the coefficients are not the smallest whole numbers. It would be necessary to divide all coefficients by 2 to reach the final equation.
Step 4 Check your answer. Count the numbers and kinds of atoms on both sides of the equation to make sure they’re the same: