AP* Chemistry
GASES
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© 2008 by René McCormick. All rights reserved.
Early barometer
THE PROPERTIES OF GASES
Only 4 quantities are needed to define the
state of a gas
:
a) the
quantity
of the gas,
n
(in moles)
b) the
temperature
of the gas,
T
(
in KELVINS)
c) the
volume
of the gas,
V
(in liters)
d) the
pressure
of the gas,
P
(in atmospheres)
A gas uniformly fills any container, is easily compressed & mixes completely with any other gas.
GAS PRESSURE
:
A measure of the force that a gas exerts on its container.
Force is the physical quantity
that interferes with inertia.
Gravity is the force responsible for weight.
Force = mass × acceleration; Newton’s 2
nd
Law.
The units of force follow:
N
=
kg
×
m/s
2
Pressure
-- Force/ unit area; N/m
2
Barometer
--invented by Evangelista Torricelli in 1643; uses the height of a column of
mercury to measure gas pressure (especially atmospheric)
1 mm of Hg = 1 torr
760.00 mm Hg = 760.00 torr =1.00 atm = 101.325 kPa
≈
10
5
Pa
At sea level all of the above define STANDARD PRESSURE.
The SI unit of
pressure is the Pascal (Blaise Pascal); 1 Pa = 1 N / m
2
The
manometer
—a device for measuring the pressure of a gas
in a container.
The pressure of the gas is given by h [the
difference in mercury levels] in units of torr (equivalent to mm
Hg).
a)
Gas pressure = atmospheric pressure –
h
b)
Gas pressure = atmospheric pressure +
h
Exercise 1
Pressure Conversions
The pressure of a gas is measured as 49 torr. Represent this pressure in both atmospheres and pascals.
6.4 × 10
-2
atm
6.5 × 10
3
Pa