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 Avagodro's Hypothesis and Molar Volume

Mole Conversions

Avogadro's Law proposed by Amedeo Avogadro

States that under equal conditions of temperature and pressure, equal volumes of gases contain an equal number of molecules.

Aug. 2003 #20. At the same temperature and pressure, 1.0 liter of CO(g) and 1.0 liter of CO2(g) have

A. equal masses and the same number of molecules
B. different masses and a different number of molecules
C. equal volumes and the same number of molecules
D. different volumes and a different number of molecules

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 C

Jan. 2010# 22 Which rigid cylinder contains the same number of gas molecules at STP as a 2.0-liter rigid cylinder containing H2(g) at STP?
(1) 1.0-L cylinder of O2(g)
(2) 2.0-L cylinder of CH4(g)
(3) 1.5-L cylinder of NH3(g)
(4) 4.0-L cylinder of He(g)

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 2

Jan 2009 #17 Which two samples of gas at STP contain the same total number of molecules?
(1) 1 L of CO(g) and 0.5 L of N2(g)
(2) 2 L of CO(g) and 0.5 L of NH3(g)
(3) 1 L of H2(g) and 2 L of Cl2(g)
(4) 2 L of H2(g) and 2 L of Cl2(g)

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 4

Jan 2002 15 At the same temperature and pressure, which sample contains the same
number of moles of particles as 1 liter of O2(g)?

(1) 1 L Ne(g)      (3) 0.5 L SO2(g)
(2) 2 L N2(g)       (4) 1 L H2O(ℓ)

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 1

Molar Volume of a Gas

This hypothesis was not acknowledged in Avogadro's lifetime and it wasn't until Stanislao Cannizzaro, in 1860, demonstrated that it was the solution to the problem of atomic and molecular weights that Avogadro's Law became widely accepted. The number of particles in one mole of a substance was named Avogadro's number in his honor, and is numerically equal to 6.02252 x 10 23

from-http://www.chemsoc.org/timeline/pages/1811.html

Avogadro’s law, which is derived from this basic idea, says that the volume of a gas maintained at constant temperature and pressure is directly proportional to the number of moles of the gas, or

V = constant x n (where n is the number of moles of the gas)

$P \cdot V = n \cdot R \cdot T$

which can be rearranged thus:

$\frac{V}{n} = \frac{R \cdot T}{P}$

P = the gas absolute pressure, in atm

n = number of moles, in mol

V = the volume, in L

T = the gas absolute temperature, in K

R = the universal gas law constant of 0.0821 L·atm/(mol·K)

1 mole of gas is calculated to be 22.4L/mole of a gas @STP.

 V= nRT = (1 mol)(0.0821)(273K) = 22.4L at STP P 1 atm

Mole Conversions