1. Pressure and Temperature
William Thomson
“Lord Kelvin”

2. CA Standards
Students know the values and meanings of standard temperature and pressure (STP).
Students know how to convert between the Celsius and Kelvin temperature scales.
Students know there is no temperature lower than 0 Kelvin.

3. Measuring Pressure The first device for measuring atmospheric
pressure was developed by Evangelista Torricelli
during the 17th century.
The device was called a “barometer”
Baro = weight
Meter = measure

4. An Early Barometer
The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.

5. Pressure
is caused by the collisions of molecules with the walls of a container
is equal to force/unit area
can be measured using a variety of units

6. Pressure Pressure is the force created by the collisions
of molecules with the walls of a container
Unit
Symbol
Definition/Relationship
Millimeter of mercury
mm Hg
Pressure that supports a 1 mm column of mercury in a barometer
Torr
torr
1 torr = 1 mm Hg
Pascal Pa
SI pressure unit
1 Pa = 1 newton/meter2
Atmosphere
atm
Average atmospheric pressure at sea level and 0 C

7. Standard Pressure 760 torr 760 mm Hg (millimeters of mercury)
101.3 kPa (kilopascals)
1 standard atmosphere (atm)

8. Converting Pressure Units
Gas law problems involving pressure require that the pressure be in the SAME UNITS!
1 atm = kPa = 760 mm Hg
Converting kPas to atms
x atms = ____ kPas
1atm kPa
Converting kPas to mm Hg
x mm Hg = ____ kPas
760 mm Hg kPa

9. Converting Pressure Units
1 atm = kPa = 760 mm Hg
A gas sample has a pressure of mmHg. What is the pressure of this gas sample in atmospheres and in kilopascals?
Converting mm Hg to atms
x atms = 800 mm Hg
1atm mm Hg
Converting mm Hg to kPas
x kPas = 800 mm Hg
101.3 kPa 760 mm Hg
x = atm
x = kPa

10. Converting Pressure Units
1 atm = kPa = 760 mm Hg
A tank of oxygen is under a pressure of about 4.00 x 103 kPa. Express this pressure in millimeters of mercury.
Converting kPas to mm Hg
x mm Hg = 4 x 103 kPas
760 mm Hg kPa
x = 3.00 x 104 mm Hg

11. Air Pressure has many applications (in real life!)
Here’s one of those applications !

12. The Kelvin Scale

13. Standard Temperature Standard Temperature equals: 273 Kelvin (273 K)
0 C

14. Converting Celsius to Kelvin
Gas law problems involving temperature require that the temperature be in KELVINS!
Kelvins = C + 273
°C = Kelvins - 273

15. Standard Temperature and Pressure “STP”
Either of these:
273 Kelvin (273 K)
0 C
Standard Temperature and Pressure “STP”
And any one of these:
1 atm
101.3 kPa
760 mm Hg
760 torr