1. Gases

2. The Nature of Gases Gases expand to fill their containers
Gases are fluid – they flow
Gases have low density
1/1000 the density of the equivalent liquid or solid
Gases are compressible
Gases effuse and diffuse

3. 1) Which statement about atmospheric pressure is false? 
A) As air becomes thinner, its density decreases.
B) Air actually has weight.
C) With an increase in altitude, atmospheric pressure increases as well.
D) The colder the air, the lower the atmospheric pressure

4. Ideal Gases Ideal gases are imaginary gases that perfectly
fit all of the assumptions of the kinetic molecular theory.
Gases consist of tiny particles that are
far apart relative to their size.
Collisions between gas particles and between
particles and the walls of the container are
elastic collisions
No kinetic energy is lost in elastic
collisions

5. Ideal Gases (continued)
Gas particles are in constant, rapid motion.
They therefore possess kinetic energy, the
energy of motion
There are no forces of attraction
between gas particles
The average kinetic energy of gas
particles depends on temperature, not
on the identity of the particle.

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

7. 2) A gas at a pressure of 10.0 Pa exerts a force of __________ N on an area of 5.5 m2
B) 0.55
C) 5.5
D) 1.8
E) 18

8. Standard Pressure 1 standard atmosphere (atm) 101.3 kPa (kilopascals)
14.7 lbs/in2
760 mm Hg (millimeters of mercury)
760 torr

9. 3) A pressure of 1.00 atm is the same as a pressure of __________ of mm Hg.
A) 193 B) 101 C) 760 D) 29.9 E) 33.0

10. 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

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

12. 4) In a Torricelli barometer, a pressure of one atmosphere supports a 760 mm column of mercury. If the original tube containing the mercury is replaced with a tube having twice the diameter of the original, the height of the mercury column at one atmosphere pressure is __________ mm.
A) 380
B) 760
C) 1.52x103
D) 4.78 x 103
E) 121

13. The Kelvin Scale

14. 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
14.7 lbs/in2 (psi)
760 mm Hg
760 torr

15. A) a gas is made up of molecules
4) One significant difference between gases and liquids is that __________.
A) a gas is made up of molecules
B) a gas assumes the volume of its container
C) a gas may consist of both elements and compounds
D) gases are always mixtures
E) All of the above answers are correct.