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CH_301-Sutcliffe-HW7 - romasko(qrr58 Homework 7...

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romasko (qrr58) – Homework 7 – sutcliffe – (50985) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points A gas has a pressure of 5 . 87973 atm when its volume is 3 . 45 L. What will the pressure be when the volume is changed to 1 . 09855 L, assuming constant temperature? Express the final pressure in torr. Correct answer: 14033 . 6 torr. Explanation: V 1 = 3 . 45 L V 2 = 1 . 09855 L P 1 = 5 . 87973 atm P 2 = ? By Boyle’s law, P 1 V 1 = P 2 V 2 P 2 = P 1 V 1 V 2 = (5 . 87973 atm) (3 . 45 L) 1 . 09855 L · parenleftbigg 760 torr atm parenrightbigg = 14033 . 6 torr 002 10.0 points For an ideal gas, pressure has what relation- ship to volume provided only pressure and volume are allowed to change? 1. proportional 2. unrelated 3. inversely proportional correct 4. equal Explanation: Boyle’s law, P = k 1 V or P 1 V , relates the volume and pressure of a sample of gas at constant temperature. This relationship is an inverse proportionality. 003 10.0 points Which of the following is a true statement about a fixed amount of ideal gas at constant pressure? 1. If a sample of gas is heated from 100 C to 200 C, the volume will decrease by a factor of two. 2. If a sample of gas is heated from 0 C to 273 C, the volume will double. correct 3. If a sample of gas is cooled from 400 C to 200 C, the volume will decrease by a factor of two. Explanation: Volume is directly proportional to temper- ature expressed on the Kelvin scale. 0 C 270 C: 0 C + 273 = 273 K; 273 C + 273 = 546 K. The Kelvin temperature changes by a factor of 2 parenleftbigg i . e ., 546 273 parenrightbigg , so the volume would also double. 400 C 200 C: 400 C + 273 = 673 K; 200 C + 273 = 473 K. The Kelvin temperature changes by a fac- tor of 0.70 parenleftbigg i . e ., 473 546 parenrightbigg , so the volume would change by a factor of 0.70. A temperature increase from 100 C to 200 C would cause the volume to increase, not decrease, so this response must be incor- rect. 004 10.0 points A sample of a gas occupies 1580 mL at 26 . 8 C and 740 torr. What volume would it occupy at the same pressure and 175 C? Correct answer: 2361 mL. Explanation: T 1 = 26 . 8 C + 273 = 299 . 8 K V 1 = 1580 mL T 2 = 175 C + 273 = 448 K Charles’ law relates the volume and abso- lute (Kelvin) temperature of a sample of gas: V 1 T 1 = V 2 T 2 V 2 = V 1 T 2 T 1 = (1580 mL) (448 K) 299 . 8 K
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romasko (qrr58) – Homework 7 – sutcliffe – (50985) 2 = 2361 mL 005 10.0 points A 764 mL gas sample at STP is compressed to a volume of 177 mL, and the temperature is increased to 30 C. What is the new pressure of the gas in Pa? Correct answer: 4 . 85419 × 10 5 Pa. Explanation: V 1 = 764 mL V 2 = 177 mL T 1 = 0 C + 273 = 273 K P 1 = 1 atm T 2 = 30 C + 273 = 303 K P 2 = ?
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