Unit 5: Gases – Temperature &
Pressure Relationships: GayLussac’s Law
11.08 & 09 Ms. Boon Chemistry
Objectives:
•I can define Standard
temperature and pressure.
•I can state Gay-Lussac’s Law
and use it to solve problems
involving pressure and
temperature.
Agenda
Catalyst
• What is air pressure?
How do we measure air
pressure?
• Catalyst
• Soda Can Crush
• Pressure and
Temperature
HW: Complete today’s
• STP
practice problems. Pp. 445
• Exit Slip
#3, 9, 10, 24, 25
Homework Review
• The name of the gas law relating pressure and
volume is called Boyle’s Law. Boyle’s law states
that pressure and volume are inversely
proportional, if the temperature is kept constant.
▫ This means:




if pressure increases, volume decreases.
If pressure decreases, volume increases.
If volume increases, pressure decreases.
If volume decreases, pressure increases.
Homework Review
• The name of the gas law relating volume and
absolute temperature is Charles’s law. Charles’s
Law states that volume and absolute
temperature are directly proportional, if the
pressure is kept constant.
▫ This means:




If temperature increases, volume increases.
If temperature decreases, volume decreases.
If volume increases, temperature increases.
If volume decreases, temperature decreases.
Homework Review
• The name of the gas law relating pressure and
pressure and absolute temperature is GayLussac’s law. Gay-Lussac’s law states that
pressure and absolute temperature are directly
proportional, if the volume is kept constant.
▫ This means:




If pressure increases, temperature increases.
If pressure decreases, temperature decreases.
If temperature increases, pressure increases.
If temperature decreases, pressure increases.
Homework Review
• Avogadro’s law expresses the direct relationship
between amount of gas molecules and the
volume of gas, if temperature and pressure are
kept constant.
▫ This means:
 If the number of gas particles increases, the volume
increases.
 If the number of gas particles decreases, the volume
decreases.
Soda Can Crush
• The demonstration shows the relationship
between ___________ and ____________.
• As temperature increases, pressure
___________________. As temperature
decreases, pressure ___________.
Soda Can Crush
• Summary of Procedure: (1) A small amount of water
(~15 mL) is poured into an empty soda can. (2) The can
is heated until steam comes out and the water boils for
about 30 seconds. (3) Then the can is quickly plunged
upside down into ice cold water.
Hypothesis: What do you
think will happen to the can
when it is put into the ice
cold water? Why?
Soda Can Crush: Explanation
• Describe what happened using the kinetic
molecular theory of gases!
•When we put the can on the hot
plate, the temperature of the gas
inside the can increases.
•But the air pressure inside and
outside the can remain the same
because the can is open.
•When we flip the can over and
dunk it in the icy water, the
temperature of the gas decreases.
•This causes a decrease in pressure.
•When the pressure outside the can
is more than inside, the can
crushes.
Gay-Lussac’s Law: Temperature
and Pressure Relationships
• In 1802, Joseph Gay-Lussac discovered that gas
pressure and Kelvin Temperature are directly
proportional at constant volume.
•For example, if the absolute
temperature (temperature expressed in
Kelvin) is doubled, the pressure is
doubled. If the pressure is cut in half,
the absolute temperature is also cut in
half.
• When gas volume is held constant, the
following equation expresses the pressure
and temperature relationship:
If any three of the variables in
the above equation are known,
then the unknown fourth
variable can be calculated.
• Example 1: P1 = 100 mm Hg, T1 = 50 K, P2 = ??,
T2 = 100 K
• Example 2: At 273K, the pressure of a sample of
nitrogen is 1000 atm. What will the temperature
be at 250 atm?
• Example 3: At 500K, a 5 L sample of oxygen has
a pressure of 760 torr. If the temperature
doubles, what will the new pressure be?
Pressure and Temperature Unit
Conversions
• Example Pressure problem (#7)
320 mm Hg = ________ atm
• Standard Temperature and Pressure:
•
STP stands for Standard Temperature and
pressure. It is a term used in Chemistry to indicate
that an experiment or measurement was recorded when
the temperature was 0° C and the air pressure was 1
atm. STP is a number (or CONDITION) that we can
use in calculations that does not change.
•
If you see STP (standard temperature and pressure)
you should immediately think:
0° C (or 273K) and 1 atm (or 760 torr or 760 mm Hg)
STP = 0° C (or 273K) and 1 atm (or 760 torr or
760 mm Hg)
• Example: A chemist has a 10 L sample of fluorine gas
at standard temperature and pressure. If the volume is
kept constant and the temperature is increased to 300K.
What is the new pressure?
Exit Slip 4c
1. At constant volume, as temperature increases,
pressure __________. Pressure and temperature are
_________ proportional.
2. T1 = 300K, P1 = 1000 mm Hg, T2 = 900 K, P2= ___?
3. A 10 mL sample of hydrogen gas exerts a pressure of
150 torr at a temperature of 300K. When the pressure
changes to 50 torr, what is the new temperature?
4. What is standard temperature and pressure in Kelvin
and atmospheres?
5. What is the new temperature when a sample of gas at
standard temperature and pressure is decreased to 0.5
atm?