Question

Arrange the following in decreasing order of the number of molecules contained in: (A) 16 g of O$_2$, (B) 16 g of CO$_2$, (C) 16 g of CO, (D) 16 g of H$_2$

• A. (A), (B), (C), (D)
• B. (D), (C), (A), (B)
• C. (B), (A), (D), (C)
• D. (C), (B), (D), (A)

Answer 1

The Correct Option is B

The given question requires us to arrange the substances based on the number of molecules present in 16 grams of each. To do this, we must calculate the number of moles in 16 g of each substance, as the number of molecules is proportional to the number of moles. The number of moles can be calculated using the formula: 

moles = mass / molar mass

• O₂: The molar mass is 32 g/mol. The moles in 16 g = 16 g / 32 g/mol = 0.5 moles.
• CO₂: The molar mass is 44 g/mol. The moles in 16 g = 16 g / 44 g/mol ≈ 0.364 moles.
• CO: The molar mass is 28 g/mol. The moles in 16 g = 16 g / 28 g/mol ≈ 0.571 moles.
• H₂: The molar mass is 2 g/mol. The moles in 16 g = 16 g / 2 g/mol = 8 moles.

Now, we rearrange these based on the number of moles:

1. H₂: 8 moles
2. CO: ≈ 0.571 moles
3. O₂: 0.5 moles
4. CO₂: ≈ 0.364 moles

Thus, the order in decreasing number of molecules is (D), (C), (A), (B).

Answer 2

To arrange the given substances in decreasing order of the number of molecules, we need to calculate the number of moles for each substance and then relate it to the number of molecules using Avogadro's number.

(A) 16 g of O₂

Molar mass of O₂ = 2 × 16 g/mol = 32 g/mol

Moles of O₂ = 16 g / 32 g/mol = 0.5 mol

Number of molecules = 0.5 mol × Avogadro's number (N_A)

(B) 16 g of CO₂

Molar mass of CO₂ = 12 g/mol + 2 × 16 g/mol = 44 g/mol

Moles of CO₂ = 16 g / 44 g/mol ≈ 0.36 mol

Number of molecules ≈ 0.36 mol × N_A

(C) 16 g of CO

Molar mass of CO = 12 g/mol + 16 g/mol = 28 g/mol

Moles of CO = 16 g / 28 g/mol ≈ 0.57 mol

Number of molecules ≈ 0.57 mol × N_A

(D) 16 g of H₂

Molar mass of H₂ = 2 × 1 g/mol = 2 g/mol

Moles of H₂ = 16 g / 2 g/mol = 8 mol

Number of molecules = 8 mol × N_A

Now, let's compare the number of moles:

H₂: 8 mol

CO: ≈ 0.57 mol

O₂: 0.5 mol

CO₂: ≈ 0.36 mol

Therefore, the decreasing order of the number of molecules is:

(D) > (C) > (A) > (B)

The correct answer is:

Option 2: (D), (C), (A), (B)