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chem 1b mid tern 1 - Midterm I Version B Information you...

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Midterm I Version B Information you may (or may not) find useful Constants constant value unit Planck’s constant ( h ) 6 . 626 × 10 - 34 J · s Rydberg constant ( R H ) 2 . 178 × 10 - 18 J speed of light 2.997924 × 10 8 m/s Avogadro’s number 6 . 022 × 10 23 gas constant (R) 8 . 31451 J/K · mol gas constant (R) 0 . 08206 L · atm/K · mol electron charge ( e ) 1 . 6022 × 10 - 19 C electron mass 9 . 1094 × 10 - 31 kg Proton mass 1 . 67252 × 10 - 27 kg Neutron mass 1 . 67495 × 10 - 27 kg 1
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1 ldeal Gas Law Consider an expandable balloon filled with 6.20 g of CH 4 gas. The pressure of the gas is the same as the outside pressure (1.00 atm) and the volume is 10.0 L. a What is the temperature of the gas? n = 6 . 20 g 16 . 04 g/mol = 0 . 387 mol of CH 4 T = pV nR = 1 . 00 × 10 . 0 0 . 387 × 0 . 08206 = 315 K Answer: 315 K 6 points b The weather changes. The pressure rises to 1.10 atm and the balloon expands to 11.2 L. Calculate the new temperature of the gas. T 2 = T 1 p 2 V 2 p 1 V 1 = 315 × 1 . 10 × 11 . 2 1 . 00 × 10 . 0 = 388 K Answer: 388 K 6 points c Consider another expandable balloon with a volume of 8.00 L at 1.00 atm and 15.0 o C. Given that the total mass of the gas is 10.26 g, calculate the molar mass of the gas. d = m/V = 10 . 26 g/ 8 . 00 L = 1 . 283 g/L M = dRT p = 1 . 283 × 0 . 08206 × 288 . 15 1 . 00 = 30 . 34 g/mol Answer: 30.3 g/mol 8 points 2
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2 Partial Pressure A 10.0 L cylinder at 1.00 atm and 21.0 o C contains F 2 gas. a Calculate the number of moles of the gas in the cylinder. n = pV RT = 1 . 00 × 10 . 0 0 . 08206 × (21 . 0+273 . 15) = 0 . 414 mol of F 2 Answer: 0.414 mol 6 points b The cylinder is connected to a second cylinder with a valve. The second cylinder has a vol- ume of 5.00 L and contains 0.800 mol of SO 2 gas. After opening the valve, the gases mix and the temperature decreases to 18.5 o C. Calculate the partial pressure of SO
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