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Unformatted text preview: Chapter M - Problems Blinn College - Physics 2425 - Terry Honan Problem M.1 30 g of water is placed in a 2.5 liter pressure cooker and heated up to 350 °C. What is the pressure inside the cooker assuming no gas escapes and neglecting the gas that was initially inside it? Solution to M.1 The mass of a molecule in u gives the mass of a mole in g. (This is because one mole is N A , Avogadros number, of molecules and N A u = 1 g .) m H 2 O = 2 m H + m O = 2 μ 1 u + 16 u = 18 u ï m mole = 18 g The number of moles is: m tot = n m mole ï n = m tot m mole = 30 18 = 1.667 moles The ideal gas law gives the pressure. P = n R T V = n 8.31 H 273 + 350 L 2.5 μ 10- 3 = 3.45 μ 10 6 Pa Problem M.2 A spherical weather balloon can expand to a volume with radius 25 m when it is at the extreme height where the pressure is 0.04 atm and where the temperature is - 70 °C. What is its radius when it is near the ground at 1 atm and 25 °C? Solution to M.2 The volume of a sphere is proportional to its radius. V = 4 3 p r 3 ï V 2 V 1 = r 2 r 1 3 . The ideal gas law, P V = n R T with a constant n gives P 2 P 1 V 2 V 1 = T 2 T 1 ï P 2 P 1 r 2 r 1 3 = T 2 T 1 ï 1 0.04 K r 2 25 O 3 = 273 + 25 273- 70 ï r 2 = 9.72 m Problem M.3 A tank contains some unknown gas that may be treated as ideal. When the tank contains 8 kg of gas, the pressure gauge on the tank reads 30 atm. After gas is let out of the tank and the temperature is allowed to return to its earlier value the gauge reads 12 atm. Whatreads 30 atm....
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This document was uploaded on 02/01/2010.
- Spring '09