Useful Constants: 1 Torr = 133.32 Pa; R = 8.3145 J/mol·K You have a thin metal s

Question

Useful Constants: 1 Torr = 133.32 Pa; R = 8.3145 J/mol·K

You have a thin metal sphere of unknown volume that contains helium gas. You hold the entire metal sphere in the room temperature water bath (measured to be 21.0 °C), and a pressure gauge on the sphere indicates a pressure of 145 kPa.

a) You now place the metal sphere in boiling water. What is the new pressure? 184 kPa b) You now place the metal sphere in ice water. What is the new pressure? 134.6 kPa c) You now place the metal sphere in a mixture of dry ice and methanol. What is the new pressure? 96.2 d) You now place the metal sphere in a liquid nitrogen bath. What is the new pressure? 38.0 kPa e) Given that the volume of the metal sphere, pressure gauge, etc., was 331 mL, how many moles of helium gas would you have? 0.0184 x mol

Explanation / Answer

We can use PV = nRT for part e

V = 331 x 10-3 L

= 331 x 10-6 m3

P = 145 x 103 Pa

T = 21 +273 K

= 294 K

PV = nRT

(145 x 103 )(331 x 10-6) = n (8.3145)(294)

n = 0.0196 moles

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