Question

$20\,mL$ of methane is completely burnt using the $50\,mL$ of the oxygen. The volume of the gas left after cooling to the room temperature is:
A. $80\,mL$
B. $40\,mL$
C. $60\,mL$
D. $30\,mL$

Answer 1

At first we will find what is methane and its chemical composition. Then we will find its combustion reaction of oxygen with methane. We will write with a balanced reaction. Then from that reaction we will calculate how many moles of oxygen will react to how many moles of the methane. From that comparison we will know the volume used and then the volume left of each gas.

Complete answer:
Step 1: Methane is a chemical compound whose formula is $C{H_3}$ . It has one carbon atom with four hydrogen atoms attached to it with a single covalent band. It is the simplest alkane. Methane is found in abundance on earth. It is a cheap fuel.
Step 2: The oxygen gas reacts to the methane and performs a combustion reaction. It will produce carbon dioxide and water.
The balanced reaction is given below.
$C{H_4} + 2{O_2} \to C{O_2} + 2{H_2}O$
Step3: From the above reaction we can see that $2$ moles of oxygen will be required for the combustion of $1$ mole of methane. This reaction also shows that $1$ mole of the methane will produce one mole of the Carbon dioxide and two moles of water. The same will be true if we talk in the terms of the volume
Step 4: So to combust the $20\,mL$ of the methane we need $40\,mL$ of the oxygen.
Hence the oxygen left will be $50 - 40 = 10\,mL$
The volume of $C{O_2}$ formed will be as same of the volume of the volume of methane used in:e $20\,mL$
Step 5: Hence the total volume will be $20 + 10 = 30\,mL$ left after cooling of the room temperature.

**Hence the option D is the correct answer.

Note:**
Methane is widely used as the fuel for many things. It is a major part of natural gas. It is used as the fuel in gas turbines or the steam generators. The ratio of the carbon dioxide to the unit of heat released is less than any of the other fuels.