Question

Leslie incorrectly balances an equation as 2C4H10 + 12O2 → 8CO2 + 10H2O. Which coefficient should she change? A.)2 B.)8 C.)10 D.)12

Answer 1

Answer: Option (D) is the correct answer.

Explanation:

In the equation, number of molecules of carbon, hydrogen and oxygen on the reactant and product side are as follows.

           $C_{4}H_{10} + O_{2}\rightarrow CO_{2}+ H_{2}O$

No. of carbon atoms on reactant side = 4

No. of hydrogen atoms on reactant side = 10

No. of oxygen atoms on reactant side = 3

No. of carbon atoms on product side = 1

No. of hydrogen atoms on product side = 2

No. of oxygen atoms on product side = 3

Balance the product side by multiplying no. of carbon atoms with 4 and no. of hydrogen atoms with 5. Therefore, the equation will be as follows.

        $C_{4}H_{10} + O_{2}\rightarrow 4CO_{2}+ 5H_{2}O$

Now, the no. of oxygen atoms on product side is 8 + 5 = 13. The no. of oxygen atoms on reactant side 2.

Thus, multiplying the no. of oxygen atoms on reactant side by $\frac{13}{2}$. Therefore, the equation will become as follows.

      $C_{4}H_{10}$ + $\frac {13}{2}O_{2}\rightarrow 4CO_{2}+ 5H_{2}O$

Multiply the whole equation by 2, then the equation will be as follows.

$2C_{4}H_{10}$ + $13O_{2}\rightarrow 8CO_{2}+ 10H_{2}O$

Thus, we can conclude that the coefficient 12 should be changed by Leslie.

Answer 2

Answer: D.) 12

Explanation: $2C_4H_{10}+12O_2\rightarrow 8CO_2+10H_2O$

According to the law of conservation of mass, mass can neither be created nor be destroyed, and remains conserved. The mass of products must be same as that of the reactants.

Thus the number of atoms of each element must be same on both sides of the equation so as to keep the mass same and thus balanced chemical equations are written.

The number of atoms of oxygen are 26 ( 16 in $CO_2$ and 10 in $H_2O$) on product side and 24 (in $O_2$) on reactant side. Thus the coefficient 12 must be changed to 13 so that the number of atoms on the reactant side is also equal to 26 and a balanced chemical equation results.

The balanced chemical equation is:

$2C_4H_{10}+13O_2\rightarrow 8CO_2+10H_2O$