Question
Question: Which of the following contains the maximum number of molecules? (A) 1 gm of \(C{{O}_{2}}\) ...
Which of the following contains the maximum number of molecules?
(A) 1 gm of CO2
(B) 1 gm of N2
(C) 1 gm of H2
(D) 1 gm of CH4
Solution
For a molecule, molecular weight in grams is equal to the Avogadro number. By calculating the molar mass of each given compound and then equating it with the above relation we would get the compound which is having the highest number of molecules.
Complete step by step answer:
- Let's start with the idea of Avogadro number and concept of moles. Avogadro’s number can be defined as a proportion that relates molar mass on an atomic scale to physical mass on a human scale. It is defined as the number of elementary particles such as molecules, atoms, compounds, etc. per mole of a substance.
- Or in other words, the number of units in one mole of any substance is called Avogadro’s number or Avogadro’s constant. Its value is given as 6.023×1023.
- Avogadro number is often denoted as NA.
- An additional property of Avogadro’s number is that the mass of one mole of a substance is equal to that substance’s molecular weight. Also, the gram atomic mass of an element is the mass of one mole of that element and the gram molecular mass of a compound refers to the mass of a single mole of the compound.
-Let's consider CO2. By the above definition the gram atomic mass of CO2 an be found.
For CO2the molar mass
= 12+(16×2) ( since ,molar mass of Carbon =12 and molar mass of oxygen =16)
= 44 g
By the definition of Avogadro's number, we can write
Number of molecules of in 44 g of CO2 =6.023×1023
Therefore in 1 g of CO2= 446.023×1023
= 1.37×1022molecules
For N2 the molar mass is 28 g.
Hence number of molecules in 28 g of N2= 6.023×1023
∴ In 1 g of N2=286.023×1023
= 2.15×1022 molecules
For H2the molar mass is 2 g.
Hence number of molecules in 2 g of H2= 6.023×1023
∴ In 1 g of H2 = 26.023×1023
= 3.011×1023 molecules
For CH4 the molar mass is 16 g.
Hence number of molecules in 16 g of CH4=6.023×1023
∴ In 1 g of CH4 =166.023×1023
= 3.76×1022 molecules
So, the correct answer is “Option C”.
Note: We could also find the answer in a simpler way. The given mass is the same for all the four gases.
Therefore, the gas having lowest molar mass will have maximum number of moles and maximum number of molecules. Among the given options H2 is having the lowest molar mass (2 g). Hence H2 will have a maximum number of molecules.