Question

c4h10 + o2 → co2 + h2o
how many molecules of o2 are needed to balance the equation?
a. 7
b. 12
c. 13
d. 26

Explanation:

Step1: Balance carbon atoms

First, balance the carbon atoms. In $C_4H_{10}$, there are 4 carbon atoms. So, we need 4 moles of $CO_2$ on the right - hand side: $C_4H_{10}+O_2
ightarrow4CO_2 + H_2O$.

Step2: Balance hydrogen atoms

In $C_4H_{10}$, there are 10 hydrogen atoms. So, we need 5 moles of $H_2O$ on the right - hand side to balance the hydrogen atoms: $C_4H_{10}+O_2
ightarrow4CO_2+5H_2O$.

Step3: Balance oxygen atoms

On the right - hand side, in 4 moles of $CO_2$ there are $4\times2 = 8$ oxygen atoms, and in 5 moles of $H_2O$ there are 5 oxygen atoms. So, in total there are $8 + 5=13$ oxygen atoms on the right - hand side. Since oxygen is $O_2$, we need $\frac{13}{2}$ moles of $O_2$ for the un - integer coefficient case. But if we multiply the whole equation by 2 to get rid of the fraction, we have $2C_4H_{10}+13O_2
ightarrow8CO_2 + 10H_2O$. So, 13 molecules of $O_2$ are needed to balance the equation.

Answer:

C. 13