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CHEM 0110
QUIZ 6
WEEK 8
MONDAY, 1:00 PM
October 18, 2010
NAME_______________________________________________________________________
pV = nRT;
u
=
2
1
mass
molar
RT
3
;R = 0.0821 L atm/mol K = 8.31 J/mol K
1. Assess each of the following statements as True or False. Give your reasoning.
a) Volume is directly proportional
to Temperature at constant pressure and # of moles of
gas.
b) Volume is directly proportional
to pressure at constant temperature and # of moles
c) A gas behaves more ideally at low temperature than at high temperature.
2.
A certain gas, in a closed metal container of volume 4.33L, had a pressure of
0.973atm at a temperature of 48
°
C. The mass of this sample of gas was found to be
6.71g.
a)
Determine the molar mass in g/mol of the gas.
b)
If the empirical formula of the gas is CH
2
, deduce the molecular formula.
ANSWERS
1.
a) True. As pV = nRT, as T increases at constant p, V will also increase.
b) False. As pV = nRT, if the righthand side is constant, an increase in V must be
accompanied by a decrease in p, which is an inverse proportionality.
c) False. A gas is more ideal at high temperature. At low temperature, the collisions
between molecules become inelastic (sticky). OR, at low temperature the gas
condenses to a liquid.
2.
a) The gas density =
6.71g
4.33L
= 1.55g/L
d =
p (MM)
RT
; i.e.
(MM) = dRT/p
(MM)
=
1.55 g / L x 0.0821 L atm / mol K x 321 K
0.973 atm
=
42.0 g/mol
[Or calculate the number of moles of gas, and then molar mass = mass/# of moles]
b)
Empirical formula mass of CH
2
= 14.0 g/mol = 42.0 g/mol / 3.
Molecular formula = 3 (CH
2
) = C
3
H
6
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View Full DocumentCHEM 0110
QUIZ 6
WEEK 8
MONDAY, 6:00 PM
October 18, 2010
NAME_______________________________________________________________________
pV = nRT;
u
=
2
1
mass
molar
RT
3
R = 0.0821 L atm/mol K = 8.31 J/mol K
1. A bulb of volume 1.20L contains N
2
gas at a pressure of 3.60atm and a temperature of
19
o
C. The bulb is connected, via a (closed) valve to another bulb, which has a volume
of 4.80L and is initially evacuated (no gas, p = 0)
a) Determine the mass of N
2
gas in the 1.20L bulb.
b) When the valve is opened, the gas expands to fill both bulbs. What is the final gas
pressure, if the temperature does not change?
2.
Two balloons, one containing Xe gas and the other Ar gas, have the same volume,
pressure and temperature.
a)
Which sample has the greater mass?
b)
Which sample has the greater average molecular speed?
Give your reasoning.
ANSWERS
1.
(a) Determine the number of moles of N
2
and then the mass.
n =
pV
3.60 atm x 1.20L
=
RT
0.0821 L atm/mol K x 292K
= 0.180 mol
Mass = 0.180 mol x 28.0 g/mol = 5.05g
(b) As n and T are constant, we can use p
1
V
1
= p
2
V
2
, with p
1
= 3.60atm, V
1
= 1.20L
and
V
2
= 1.20 + 4.80 L = 6.00L.
p
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 Spring '06
 Dr.Huston
 Chemistry

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