Question

What is the inital volume of a gas at STP, if its final volume is 80.0 mL at 109 kPa and –12.5°C.

Answer 1

Apply combine gas law

`\\ \rm\Rrightarrow (P_1V_1)/(T_1)=(P_2V_2)/(T_2)`

`\\ \rm\Rrightarrow (101.325V_1)/(273)=(109(80))/(273-12.5)`

`\\ \rm\Rrightarrow 0.37V_1=33.5`

`\\ \rm\Rrightarrow V_1=90.5mL`

Answer 2

77.9 mL

Step-by-step explanation:

Initial conditions

• V₁ = ?
• P₁ = 1 atm = 101.325 kPa
• T₁ = 273 K

Final conditions

• V₂ = 80.0 mL
• P₂ = 109 kPa
• T₂ = -12.5°C = 260.5 K

Equating Inital and Final conditions

• V₁ = P₂V₂T₁/P₁T₂
• V₁ = 101.325 × 80 × 273 / 109 × 260.5
• V₁ = 2212938/28394.5
• V₁ = 77.9 mL