Question

The volumes of gases A, B, C and D are in the ratio, 1 : 2 : 2 : 4 under the same conditions of temperature and pressure.

1. Which sample of gas contains the maximum number of molecules?
2. If the temperature and pressure of gas A are kept constant, then what will happen to the volume of A when the number of molecules is doubled?
3. If this ratio of gas volume refers to the reactants and products of a reaction, which gas law is being observed?
4. If the volume of A is actually 5.6 dm³ at STP, calculate the number of molecules in the actual Volume of D at STP (Avogadro's number is 6 × 10²³).
5. Using your answer from (iv), state the mass of D if the gas is dinitrogen oxide (N₂O).

Answer 1

(i) D contains the maximum number of molecules because the volume is directly proportional to the number of molecules.

(ii) The volume will double because it is directly proportional to the number of molecules at constant temperature and pressure.

${\displaystyle \frac{{\text{V}}_1}{{\text{V}}_2}}$ = ${\displaystyle \frac{{\text{n}}_1}{{\text{n}}_2}}$

${\displaystyle \frac{{\text{V}}_1}{{\text{V}}_2}}$ = ${\displaystyle \frac{{\text{n}}_1}{2{\text{n}}_1}}$

So, V₂ = 2V₁

(iii) Gay Lussac's law of combining volume is being observed.

(iv) The volume of D = 5.6 × 4 = 22.4 dm³, so the number of molecules = 6 x 10²³ because according to mole concept 22.4 litre volume at STP has 6 x 10²³ molecules.

(v) No. of moles of D = 1 because volume is 22.4 litre.

∴ Mass of N₂O = (14 × 2 + 16 × 1) = 44 g