Lesson
,c
W
Behavior of Gases
Key Words
Boyles law
charles’s law:
STI’:
volume of a gas decreases as pressure increases
temperature remains constant
if
volume of a gas increases as temperature increases if
pressure remains constant
standard temperature and pressure (1 atm and 273 K)
The propettles a gas irickide pressaxe, vdume, end temperattae. If the size of one
proper
’ of certain amount a g changes, the remE*g pmpert)es e acIied. The size
__LJ
and direction of these changes can be coiçuted If the gas Is In a closed container.
SCUBA divers depend on Self Contained Underwater Breathing Apparatus
for working underwater salvage. To stay under water, the diver needs a
good supply of oxygen. A fairly large volume of oxygen is reduced to a
small volume under high pressure in the diver’s tanks. As the oxygen is
released slowly from the tank, the pressure on the oxygen is reduced and
the volume of the released oxygen increases.
Boyle’s Law. According to Boyle’s law (boilz law), the volume of a gas
changes inversely with the pressure of the gas if the temperature remains
constant. In an inverse proportion, one value increases as the other value
decreases. The graph in Fig. 8-1 shows this relationship for Boyle’
s law
when the gas is in a dosed container and the temperature is constant.
Fig. 8-1
E E IEEE E E E E E
:::::::::::::
——
—
—
——
—
—
—
I.
—
—
%
—
—
-
%
E E EL- E E E E E E
Volume (liters)
Utt 2
P1mes at $.meu
Boyle’s law can be written as
v
2
ply! = P
is
In this equation, P = pressure; V = volume; I is for the first value; and 2
for the second value.
Problem: A 2.00-liter balloon is filled with helium gas at a pressure of
760 tort What will be the volume of the balloon if the pressure is lowered
to 608 torr?
Solution: Substitute the values into the equation for Boyle’s law.
ply, =
(760 torr) (2.001)
2
V
v
2
P
=
)
2
(608 torr) (V
(760 torr) (2.001)
(608 torr)
2 = 2.50 1
V
1. A container wIth 8.00 Uteri of hydrogen gas has a pressure of 2.00
atm. What volume will the hydrogen occupy If the pressure Is
increased to 4.00 atm?________________________________
Charles’s Law. According to Charles’s law, the volume of a gas increases as
die Kelvin temperature increases if the pressure remains constant. The graph
in Fig. 8-2 shows this relationship for Charles’s law when the gas is in a closed
container and the pressure is constant. Charles’s law can be written as follows:
V1
1
T
-
V2
2
T
In this equation, T = temperature in Kelvin degrees; V
first value; 2 is for the second value.
=
volume; us for the
FIg. 8-2
...:
Temperature ((eIvth)
Lesson S
Sdw,4or
Ges
____
To solve the following problem, substitute the values into the equation
above. Remember to always use Kelvin temperatures.
Pmblem A 5.00-liter sample of argon gas at 27° C is heated to 77° C. What
is the new volume of the sample?
1
V
2
V
T,
2
T
-
5.001
2
V
300K 350K
(5.00 1) (350 K)
(300K)
2 = 5.831
V
-
2. lOOmiofagaslsheatedfrom22°CtolOO°C.Whattsthenew
volume of the gas?
Combined Gas Laws. The volume of a gas changes when temperature
(T)
and pressure (P) change at the same time. You can find the new volum
e of
the gas by combining the equations used earlier.
V
1
P
1
T
2
T
-
A 10,0-liter weather balloon is filled with helium at a temperature of 20°
C
and a pressure of 740 tort The balloon rises in the atmosphere
to a point
where the temperature is -30° C and the pressure is 350 tort What is
the new
volume of the balloon?
1
Ply
V
2
P
1
T
-
-
(740 torT) (10.0 1)
293K
2
V
—
—
(350 torr) (V
)
2
243K
(740 torr) (10.01) (243 K)
(293 K) (350 torr)
2
V
=
17.51
3. A 25,0-mi sample of carbon dioxIde Is at 25° C and 800 tor
of
pressure. To wtat ICeMn temperature must the gas be heated to
increase Its volume to 30.0 mlat a pressure of 900 toni
L)nt 2
Piases &
____
Scientists have set conditions of temperature and pressure to have a basis
for a comparison. These conditions are called STT’, or standard temperature
and pressure. Standard pressure is normal barometric pressure (1 atm or
(00 C
760 torr), and standard temperature is the freezing temperature of water
or 273 K).
25.00 C. How much
See Fig. 8-3. A tank holds 3.0 liters of air at 8.0 atm and
space will the air occupy at STP?
ft. 8-3
1
Ply
—
TI
(8.0 atm) (3.0 1)
298K
(1.00 atm) (298 k)
(V
)
2
2
v
2
T
-
—
—
=
(1.0 atm) (1’2)
273K
(8.0 atm) (3.0!) (273 K)
(80 atm) (30 1) (273 K)
(1.0 atm) (298 K)
2
V
=
22.01
4. A 2.OO4ter taiic of fnec oxygen gas has a p.esswe of 6.00 atm at a
temperaWre of 30.00 C. What wtfl the vokime be at STP?
GAS LAW
PROPERTTES
Boyle’s Law
Pressure
Volume
Charles’s Law
Temperature
Volume
Combined Law
Temperature
Pressure
Volunie
TAKE
Ar4OTHER
EQUATION
00k
1
V
V
-
2
T
1
T
1
1
2 v2
Leno
a
Ie*w at Ga,es
___________
______
Heating a
same.
gas
number of molecules stays the
expands, its volume increases. See Fig. 8-4. The rate of
is directly proportional to the Kelvin temperature.
causes it to expand, but the
As a gas
expansion
Fig. 8-4
Thermometer
When the pressure on a gas increases, its volume
decreases. See Fig. 8-5.
Notice that the temperature and the number of molecules of gas stay the same.
Fig. 8-5
Check Your
Understanding
5.
In
the boxes below, write the equations for the
(a)
L
Charles’s Law
(b)
I
(c)
Boyle’s Law
Use the term increases or decreases
gas changes.
gas laws.
to
Combined Law
describe what happens when a property
of a
6.
Pressure increases when volume
7.
Volume
8.
When temperature increases, volume
Volume increases when pressure
9.
UrWI 2
Ptises o Mtt,
when temperature decreases.
—
_______
_______
______
______
__________
_______________
_____________
_______________
______________
___________
____________
Define SIP in terms of
10. degrees Celsius
11. degrees Kelvin
12. pressure
in
atmospheres
13. pressure in torr
14, pressure in mm
Write a B if the statement describes Boyle’s law, C if the statement describes
Charles’s law, and STP if the statement describes standard temperature or
standard pressure.
=P
1
P
2
V
is.
0°C
16.
19.
pressure is inversely proportional to volume
2
V
7
V
2
T
1
T
760 torr
20.
1 atm
21.
volume varies with Kelvin temperature
22.
273K
23
volume decreases when temperature decreases
volume increases when pressure decreases
17.
18.
24.
—
Underline the correct answer.
25. A 100-mi sample of nitrogen gas is at a pressure of 380 torr. If the
pressure of the gas is reduced to 190 torr, the new volume is
(200 ml, 50.0 ml, 900 ml, 290 ml).
26. 30.0 mI of neon gas is at 273 K. The temperature is increased to 364 K
What is the new volume of the gas in ml? (15.0, 40.0, 60.0, 90.0)
27. 20.0 liters of acetylene gas at STP are forced into a 2.0-liter tank at 300 K.
What is the pressure of the gas in atm? (2.00, 11.0, 40.0, 546)
Lssnn
tta1cr a G.,e.