Question

A gas bottle contains 0.250 mol of gas at 730 mm hg pressure. if the final pressure is 1.15 atm, how many moles of gas were added to the bottle?

Answer 1

Answer: 0.049 mol

Explanation:

1) Data:

n₁ = 0.250 mol

p₁ = 730 mmHg

p₂ = 1.15 atm

n₂ - n₁ = ?

2) Assumptions:

i) ideal gas equation: pV = nRT

ii) V and T constants.

3) Solution:

i) Since the temperature and the volume must be assumed constant, you can simplify the ideal gas equation into:

pV = nRT ⇒ p/n = RT/V ⇒ p/n = constant.

ii) Then p₁ / n₁ = p₂ / n₂

⇒ n₂ = p₂ n₁ / p₁

iii) n₂ = 1.15atm × 760 mmHg/atm × 0.250 mol / 730mmHg = 0.299 mol

iv) n₂ - n₁ = 0.299 mol - 0.250 mol = 0.049 mol