Question

How many litres of carbon dioxide are produced when $2.0$ moles of $C{H_4}$ are burned at $STP$ ?

Answer 1

Write down the chemical equation of the combustion reaction for $C{H_4}$ and balance it. After balancing, find out the mole-to-mole ratio of $C{H_4}$ and $C{O_2}$ . We will also use the concept of $STP$ , that is, $1$ mol of a gas occupies ${\text{22}}{\text{.4}}$ litres of volume at $STP$ . The mole-to-mole ratio and $STP$ factor will help us in finding the litres of $C{O_2}$ produced on burning of ${\text{2}}$ moles of $C{H_4}$ .

Complete answer:
When methane $(C{H_4})$ undergoes combustion, then the following reaction takes place where methane on burning gives carbon dioxide as well as hydrogen.
$C{H_4} + 2{O_2}\xrightarrow{\Delta }C{O_2} + 2{H_2}O$
From the balanced equation above, we can see that the mole ratio of $C{H_4}:C{O_2}$ is $1:1$ or that $1$ mol of $C{H_4}$ gives $1$ mol of $C{O_2}$ . Therefore, on burning ${\text{2}}$ moles of $C{H_4}$ , it will produce ${\text{2}}$ moles of $C{O_2}$ .
Now, at $STP$ , ${\text{1}}$ mol of a gas occupies a volume of ${\text{22}}{\text{.4}}$ litres or we can say that ${\text{1 mol}}$ of a gas is equal to ${\text{22}}{\text{.4}}$ litres of that gas. Since, ${\text{1 mol}}$ of $C{H_4}$ on burning gives $1$ mol of $C{O_2}$ , we can say that we get ${\text{22}}{\text{.4}}$ litres of $C{O_2}$ . Thus, when ${\text{2}}$ moles of $C{H_4}$ is burned, ${\text{2}}$ moles of $C{O_2}$ will pe produced or we can say that $2 \times 22.4 = 44.8$ litres of $C{O_2}$ will be produced.
**Hence, when ${\text{2}}$ moles of $C{H_4}$ is burned, $44.8$ litres of $C{O_2}$ will be produced.

Note: **
Balancing of the chemical equation should be performed carefully. Any error in balancing will influence the mole-to-mole ratio of $C{H_4}$ and $C{O_2}$ which will ultimately result in an incorrect solution. Keep in mind the $STP$ factor of $22.4Lmol{e^{ - 1}}$ . Also, pay close attention to the units while writing the solution.