What is the volume occupied by 2 moles of ammonia at s.t.p?

Analyze the question: You are asked for the volume of 2 moles of ammonia gas (NH₃) at s.t.p. (standard temperature and pressure).

Concept: At s.t.p. (0°C or 273 K, and 1 atm or 760 mmHg), one mole of any ideal gas occupies 22.4 dm³. This is the molar volume of a gas.

Volume = number of moles × molar volume

Solution:

Volume = n × 22.4 dm³/mol

Volume = 2 × 22.4

Volume = 44.8 dm³

Ammonia is treated as an ideal gas here, so the same molar volume applies. The kind of gas does not matter at s.t.p.

Check against the options:

• A. 44.8 dm³ matches our result.
• B. 22.4 dm³ is the volume of only 1 mole.
• C. 11.2 dm³ is the volume of 0.5 mole.
• D. 5.6 dm³ is the volume of 0.25 mole.

(The unit in the options is written as dm⁻³, which is a typing slip. The correct unit is dm³.)

Tip: For s.t.p. volume questions, remember the quick link: moles × 22.4 = volume in dm³. Just count the moles and multiply. Options that are half, quarter, or equal to 22.4 are common distractors for 0.5, 0.25, or 1 mole.