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# Hwk 7 Answers - huynh(hph268 – Homework 7 – Sutcliffe...

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Unformatted text preview: huynh (hph268) – Homework 7 – Sutcliffe – (52380) 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 4 . 24783 atm when its volume is 2 . 61 L. What will the pressure be when the volume is changed to 1 . 78903 L, assuming constant temperature? Express the final pressure in torr. Correct answer: 4709 . 81 torr. Explanation: V 1 = 2 . 61 L V 2 = 1 . 78903 L P 1 = 4 . 24783 atm P 2 = ? By Boyle’s law, P 1 V 1 = P 2 V 2 P 2 = P 1 V 1 V 2 = (4 . 24783 atm) (2 . 61 L) 1 . 78903 L · parenleftbigg 760 torr atm parenrightbigg = 4709 . 81 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. unrelated 2. inversely proportional correct 3. proportional 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 0 ◦ C to 273 ◦ C, the volume will double. correct 2. If a sample of gas is heated from 100 ◦ C to 200 ◦ C, the volume will decrease by a factor of two. 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. ◦ C → 270 ◦ C: ◦ 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 1560 mL at- 40 . 2 ◦ C and 740 torr. What volume would it occupy at the same pressure and 435 ◦ C? Correct answer: 4744 . 3 mL. Explanation: T 1 =- 40 . 2 ◦ C + 273 = 232 . 8 K V 1 = 1560 mL T 2 = 435 ◦ C + 273 = 708 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 = (1560 mL) (708 K) 232 . 8 K huynh (hph268) – Homework 7 – Sutcliffe – (52380) 2 = 4744 . 3 mL 005 10.0 points A 787 mL gas sample at STP is compressed to a volume of 226 mL, and the temperature is increased to 29 ◦ C. What is the new pressure of the gas in Pa?...
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Hwk 7 Answers - huynh(hph268 – Homework 7 – Sutcliffe...

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