Transcript Unit: Gas Laws

Unit 9: Gases
Gay-Lussac’s and Combined Gas Laws
After today you will be able to…
• Explain the effect on gas
properties using Gay-Lussac’s
Law and the Combined Gas Law
• Calculate an unknown pressure,
temperature, or volume by
solving algebraically
Gay-Lussac’s Law: Pressure
and Temperature
Joseph Gay-Lussac
discovered the
relationship between
temperature and
pressure.
• His name is on the gas
law that describes
this relationship.
“For a given volume
of a gas, as the
temperature of an
enclosed gas
increases, the
pressure of a gas is
directly proportional.”
Gay-Lussac’s Law: Pressure
and Temperature
We can simplify this relationship by the
formula:
P1 P2
=
T1 T2
Where,
P1, P2 = pressure in any unit (atm, kPa, or
mmHg), BUT they must match!
T1, T2 = temperature is always in Kelvin!
(Recall, just add 273 + °C)
Gay-Lussac’s Law: Example
A gas has a pressure of 103kPa at 25°C. What will the
pressure be when the temperature reaches 928°C?
P1= 103kPa
P1 P2
=
T1= 25°C +273= 298K
T
T
1
2
P2= ?
T2= 928°C+273= 1201K
(P2)
(103kPa)
=
(1201K)
(298K)
P2 = 420kPa
The Combined Gas Law
The combined gas law is a
single expression that
combines Boyle’s, Charles’s,
and Gay-Lussac’s Laws.
•This gas law describes the
relationship between
temperature, pressure, and
volume of a gas.
•It allows you to do
calculations where only the
amount of gas is constant.
RB + JC +
JG-L = BFFs!
The Combined Gas Law
Helpful hint: You are able to
get which law you need by
For example, if there is no
IfIfthere
thereisisno
nomention
mention
of
ofpressure
volume in
in
covering
the
variable
that
mention of temperature in the
1
1
2
2
theisproblem,
cover
PV up
up
and
and
you
you
are
are
not
mentioned
in
the
problem!
problem, cover T up and you are
left There
with the
relationship
between
T 4
is
no
need
to
memorize
left with the relationship between
and
andP.V.(aka
(aka
Gay-Lussac’s
Charles’s 2
Law!)
Law!)
1
individual
just memorize
the
P and V. laws,
(aka Boyle’s
Law!)
Combined Gas Law and you can
derive all of the others!
PV PV
=
T
T
The Combined Gas Law
A gas occupies 3.78L at 529mmHg and 17.2°C. At what
pressure would the volume of the gas be 4.54L if the
temperature is increased to 34.8°C?
P1 V1 P2 V2
=
P1= 529mmHg
T
T
1
2
V1= 3.78L
T1= 17.2°C + 273= 290.2K
(P2)(4.54L)
(529mmHg)(3.78L)
P2= ?
=
(307.8K)
(290.2K)
V2= 4.54L
P2 = 467mmHg
T2= 34.8°C + 273= 307.8K