 Heat
• Energy transferred due to differences in temperature
 Temperature
• Measure of the average kinetic energy of particles
composing a material
 Pressure
• Force per unit area
 Volume
• The amount of space a material occupies
 Pressure
and
volume are
indirectly related
 Pressure
and
1/volume are
directly related
1.
2.
A balloon initially occupies 12.4 L at 1.00 atm.
What will be the volume at 0.800 atm?
A sample of gas expands from 10.0 L to 30.0 L. If
the initial pressure was 1140 mm Hg, what is the
new pressure?
 Using
Boyles law
Calculate: A balloon contains 40.0 L of a gas at 101.3 kPa.
What is the volume of the gas when the balloon is brought
to an altitude where the pressure is only 10.0 kPa?
(Assume that the temperature remains constant.)
 Temperature
 At
and volume are directly related
constant pressure
 Absolute
zero
• Theoretically, point at which all motion stops.
• The temperature at which volume of a gas becomes
zero when the plot of temperature vs. volume is
extrapolated.
1. Calculate the decrease in temperature when 2.00
L at 20.0°C is compressed to 1.00 L.
2. A gas occupies 900.0 mL at a temperature of
27.0°C. What is the volume at 132.0°C?
 Temp
and pressure are directly related
 Absolute
zero
• The temperature at which the pressure of a gas
becomes zero when a plot of pressure versus
temperature for a gas is extrapolated
 -273C
= 0 K or K = C + 273
1.
Consider a container with a volume of 22.4
L filled with a gas at 1.00 atm at 273 K. What
will be the new pressure if the temperature
increases to 298K?
2. A container is initially at 47 mm Hg and 77K
(liquid nitrogen temperature.) What will the
pressure be when the container warms up to
room temperature of 25C?
3. A thermometer reads a pressure of 248 Torr at
0.0C. What is the temperature when the
thermometer reads a pressure of 345 Torr?
 STP
(standard temperature and pressure)
T = 273K (which is 0°C)
P = 1 atm, 101.3 kPa, 760 mmHg, 760 torr
V = 22.4 L (one mole of gas)
 Formula
P 1 V1 =
T1
P 2 V2
T2
 10.0
cm3 volume of a gas measured 75.6 kPa
and 60.0C is to be corrected to correspond to
the volume it would occupy at STP.
The Kinetic Molecular Theory describes IDEAL gases


Most gases approximate ideal gases and the model
works great for most gases.
Some REAL gases need adjustments
• Real gases experience electrostatic attractions.
• Real gases have volume
 PV
•
•
•
•
•
= nRT
P = pressure-measured in atm, kPa, mmHg, torr
V = volume - usually measured in L
T = temperature in K
n = number of moles (“mol”)
R = “universal gas constant”
 Calculate
R if pressure is in atm: (most
common)
(1 atm)(22.4 L) = 0.0821 atm*L/K*mol
(273 K)(1mol)
 Calculate
R if pressure is in kPa: (most
common)
(101.3 kPa)(22.4 L) = 8.312 kPa*L/K*mol
(273 K)(1mol)
 Calculate
R if pressure is in torr or mm Hg:
(rarely used)
(760 torr)(22.4 L) = 62.36 torr*L/K*mol
(273 K)(1mol)
(760 mmHg)(22.4 L) = 62.36 mmHg*L/K*mol
(273 K)(1mol)
 Calculate
the temperature of 0.500 moles of a
gas occupying a volume of 20.0 L with a
pressure of 99.9 kPa.
(99.9 kPa)(20 L)
(8.312 kPa*L/K*mol)(.5 mol)
= 480.75 K
 Calculate
the moles of a gas occupying a
volume of 500.0 mL with a temperature of
25.5C and a pressure of 755 torr.
(755 torr)(.5 L)
=
(298.5 K)(62.36 torr*L/K*mol)
0.0203 mol

Calculate the volume of 1.00 mol of H2 at STP
STP = 0C 273 K and 1.00 atm
 P = 1 atm
 V=?
 n = 1 mol
 R = 0.0821 L-atm/mol-K
 T = 273K
PV = nRT
nRT/P = V
(1 mol)(.0821L-atm/mol-K)(273 K) =
22.4 L
1 atm
That number should look familiar! It is the volume of one
mole of any gas at STP. The number from the mole map
comes from the ideal gas law.