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LEARNING GOAL Use the combined gas law to calculate the final pressure, volume,

ID: 555270 • Letter: L

Question

LEARNING GOAL Use the combined gas law to calculate the final pressure, volume, or temperature of a gas when changes in two of these properties are given and the amount of gas is constant. A sample of helium gas has a volume of 6.50 L at a pressure of 845 mmHg and a temperature of 25 °C. What is the final pres- sure of the gas, in atmospheres, when the volume and tempera- ture of the gas sample are changed to the following, if the amount of gas does not change? a. 1850 mL and 325 K b, 2.25 L and 12°C c. 12.8 L and 47 °C 8.35 VI

Explanation / Answer

From gas law relation:

P1V1 / T1 = P2V2 / T2        --------------------(1)

Given, P1 = 885 mmHg = 1.164 atm; V1 = 6.50L and T1 = 25 + 273 = 298K

(a) now, P2 = ?, V2 = 1850mL = 1.850L, T2 = 325K

from eq (1): P2 = P1V1T2 / T1 V2

P2 = 1.164 x 6.50 x 325 / 298 x 1.850

P2 = 2458.95 / 551.3

P2 = 4.46atm

(b) now, P2 = ?, V2 = 2.25L, T2 = 12 + 273 = 285K

from eq (1): P2 = P1V1T2 / T1 V2

P2 = 1.164 x 6.50 x 285 / 298 x 2.25

P2 = 2156.31 / 670.5

P2 = 3.21atm

(c) now, P2 = ?, V2 = 12.8L, T2 = 47 + 273 = 350K

from eq (1): P2 = P1V1T2 / T1 V2

P2 = 1.164 x 6.50 x 350 / 298 x 12.8

P2 = 2648.1 / 3814.4

P2 = 0.694atm