Pressure Conversions

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Pressure Conversions

• 1 atm 1.01325 x 105 Pa
• 1 bar 1 x 105 Pa
• 1 millibar (mb) 100 Pa
• 1 atm 1.01325 bar
• 1 atm 760 torr
• 1 torr 1 mm Hg

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Change volume (V) and the pressure (P) will
change (assuming that temperature and the number
of molecules are constant)
Boyles Law
PV constant
Pressure and Volume are inversely proportional
P1V1 P2V2
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A gas occupying a volume of 725mL at a pressure
of 0.970 atm is allowed to expand at constant
temperature until its pressure reaches 0.541 atm.
What is the final volume?
(725 ml)(0.970 atm) (V2)(0.541 atm)
V2 1300 ml or 1.30 L
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Change the amount of gas (n) and the volume (V)
will change (assuming that temperature and
pressure constant)
Avogadros Law
n ? V
Number of Moles and Volume are proportional
V1 V2 n1 n2

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Change the temperature (T) and the pressure (P)
will change (assuming that the volume and number
of moles are constant)
Gay-Lussacs Law
T ? P
Temperature and Pressure are proportional
P1 P2 T1 T2

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An aerosol can is under a pressure of 3.00 atm at
25?C. Directions on the can caution the user to
keep the can in a place where the temperature
does not exceed 52?C. What would the pressure of
the gas in the aerosol can be at 52?C?
3.00 atm X atm 298 K 325 K

X 3.27 atm
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Change the temperature (T) and the volume (V)
will change (assuming that the pressure and
number of moles are constant)
Charles Law
T ? V
Temperature and Pressure are proportional
V1 V2 T1 T2

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A sample of neon gas has a volume of 752mL at
25?C. What volume will the gas occupy at 50?C if
the pressure remains constant?
752 ml X ml 298 K 323 K

X 815 ml
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What we find is that everything is
interrelated The combined Gas Law n ?
constant Such that P1V1 P2V2
T1 T2
PV T

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A He filled balloon has a volume of 50.0L at 15?C
and 820mmHg. What volume will it occupy at
650mmHg and 10?C?
(50.0 L)(820 mmHg) (X L)(650 mmHg)
(288 K) (283 K)
X 62.0 L
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Ideal Gas Law!
By defining the constant we can convert the
proportionality into workable equation
PV nRT
R is a constant which changes according to units,
See Table 8.1 on page 401
R 0.08206 L.atm/mol.K R
8.314 J/mol.K
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Ideal Gas Conditions

• Negligible Interactions
• Negligible Particle Size
• High Temperature
• Low Pressure

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Standard Temperature and Pressure (STP) 0oC 1
atm
Under standard conditions, what is the volume of
1.00 mol of gas?
PV nRT
(1 atm)( V ) (1 mol)(0.08206 L.atm/mol.K)(273 K)
V 22.4 L
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How many moles of gas are in my 600 ml Pepsi
bottle? (assume that the room temperature is 22oC)
PV nRT
n
(1 atm)
(0.6 L)
(0.08206 L.atm/mol.K)
(295 K)
n 0.025 mols