A sample of helium gas at 25.0°C is compressed from 200.0 cm3 to 0.24 cm3.

Question

Its pressure is now 30.0 mmHg. What was the original pressure of the helium?  

Answer 1

From the ideal gas law, when n and T are constant, P₁V₁ = P₂V₂ and P₁ = P₂V₂ / V₁ = (30.0 mmHg) (0.24 cm³) / (200. cm³) = 0.036 mmHg.