A sample of gas occupies 2.30 L at 825 mmHg and 70.0°C. What is its volume at STP

V₂ = 2.0 Liters at STP conditions

Explanation:

Solving problem using the combined gas law

Given:

Case I Conditions           Cast II Conditions

P₁ = 825mmHg                P₂ = 760mm

V₁ = 2.30 Liters                V₂ =  ?  

T₁ = 70°C + 273 = 343K    T₂ = 0°C = 273K                  

Substitute into combined gas law assuming moles of gas remains constant; solve for unknown volume under case 2 conditions

P₁·V₁/n₁·T₁ = P₂·V₂/n₂T₂ => V₂ = P₁·V₁·T₂ / P₂·T₁  => note: in this solution, moles of gas remains constant as is disregarded in final calculation.

V₂ = (825mm)(2.3L)(273K) / (760mm)(343K) = 1.987 Liters (calculator answer) ≅ 1.9 Liters (2 sig figs based on given volume (V₁)

V₂ = 1.987 Liters ≅ 2.0 Liters (2 sig figs based on given volume (V₁)                    

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