##### (a) An ideal gas occupies a volume of 1.8 cm3 at 20°C and atmospheric pressure.

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(a) An ideal gas occupies a volume of 1.8 cm3 at 20°C and atmospheric pressure. Determine the number of molecules of gas in the container.

molecules

(b) If the pressure of the 1.8-cm3 volume is reduced to 2.4 ✕ 10−11 Pa (an extremely good vacuum) while the temperature remains constant, how many moles of gas remain in the container?

Jun 21st, 2015

PV = nRT
n = PV/RT

P = 1.00 atm
V = 1.8 cm³ = 1.8 cm³ x (1 mL / 1 cm³) x (1 L / 1000 mL) = 0.0018 L
R = 0.0821 Latm/moleK
T = 20C = 20+273.15 = 293.15K

n = (1.00 atm) x (0.0018 L) / [ (0.0821 Latm/moleK) x (293.15K) ]
n = 7.48x10^-5 moles..

finally...
7.48x10^-5 moles x (6.022x10^23 molecules / 1 mole) = 4.50x10^19 molecules.

you should probably only have 2 sig figs since 1.8 has 2 and 20 has at most 2.....

# molecules = 4.5x10^19

b)

using the same formula, we get

1atm=10^5 Pa

2.4 ✕ 10−11 Pa= ?

= 2.4 X10−11 / 10^5 atm

n = (2.4 ✕ 10−11/10^5) x (0.0018 L) / [ (0.0821 Latm/moleK) x (293.15K) ]

Jun 21st, 2015

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Jun 21st, 2015
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Jun 21st, 2015
Sep 25th, 2017
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