Solve: Helium gas has a volume of 250 mL at 0°C at 1.0 atm. What will be the final
pressure if the volume is reduced to 100 mL at 45°C?
Given: V1 = 250mL V2 = 100 mL
T1 = 00C + 273.15= 273.15 K T2 = 450C + 273.15=318.15 K P1 = 1 atm P2 = ?
Given:
P1 = 1.0 atm
V1 = 250 mL
T1 = 0°C + 273.15 = 273.15 K
P2 = ???
V2 = 100 mL
T2 = 45°C + 273.15 = 318.15 K
Solution:
Combined gas law can be used.
Mathematical expression for the combined gas law:
P1V1/T1 = P2V2/T2
Cross-multiply to clear the fractions:
P1V1T2 = P2V2T1
Divide to isolate P2:
P2 = P1V1T2 / V2T1
P2 = (1.0 atm × 250 mL × 318.15 K) / (100 mL × 273.15 K) = 2.9 atm
P2 = 2.9 atm
Answer: The final pressure will be 2.9 atm
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