Transcript The Gas Laws! - Pleasanton Unified School District

The Gas Laws!
Ch 14 Notes
Properties of Gases
• Gases are compressible because
of the space between particles.
• Factors that affect gases:
•
•
•
•
Pressure
Volume
Temperature
# of moles present
Boyle’s Law
•
•
•
•
P1V1 = P2V2
Inverse Relationship
T is constant
If one goes up, the other goes
down
• If one goes down, the other
goes up
Lung model, marshmellows, bell jar, crush the can
Boyle’s Law Sample Prob
• You and your crazy friend want
to make funny voices using
helium. You obtain a helium
tank….
The volume of the gas in the tank
is 2 L, but can fill over 200 L at
room pressure. Room
pressure is 1 atm, what was the
original pressure?
Charles’s Law
• V1 = V2
T1 T2
• Direct Relationship
• P is constant and the amount of gas
is constant
• Temperature in Kelvin !!! (°C + 273)
• As V increases, so does T
• As V decreases, so does T
• higher temp = more kinetic energy,
more collisions, so volume increases
Charles’s Law Sample Prob
• The temperature in the
supermarket is a frosty 15 °C.
When you buy your bag of chips
it occupies 1 L of space. You
leave the chips in your car for 1
hour and it reaches a
temperature of 27 °C. what is
the new volume of the bag?
Gay-Lussac’s Law
•
•
•
•
P1/T1 = P2/T2
Direct Relationship
Temp in Kelvin!!!
Volume and amount of gas is
constant
• Example: The temperature of a
gas goes from 30 °C to 50 °C.
The starting pressure is
760mmHg, what is the final
pressure?
Go To Absolute Zero Video Clip
Combined Gas Law
• P1V1/T1 = P2V2/T2
• Combines Boyle’s, Charles’, and
Gay-Lussac’s Laws
• Sample: Your mom gives you a
balloon that says “I love you!” (awh!).
When she hands it to you it has a
pressure of 1.5 atm and is at 295 K.
The next morning it is at 290 K, has a
pressure of 1.2 atm and has a
volume of 1.5 L. What was the
original volume of the balloon?
Molar Volume
• At STP, 1 mole of any gas
occupies 22.4 L
• STP = 0 °C (273 K) and 1 atm
• What will be the volume of 5
moles of gas at STP?
• A sample of gas occupies 11.2 L
at STP, how many moles is in the
sample?
• How many grams of chlorine are
in 5 L of chlorine gas at STP?
Ideal Gas Law
• relates P, V, T, and the amount of
gas in moles (n)
• PV = nRT
• R = “ideal gas law constant”
• There are many values for R -- choose
the one that agrees with your pressure
units.
• Volume must be in LITERS and
temperature in KELVIN!
• ‘ideal’ gases - particles have no volume, no
attractive/repulsive forces, don’t liquefy
under high pressure or low temperature
• real gases are ‘ideal’ gases under all
conditions except very high pressure or very
low temperature
Sample Problems…
1. You have 4 moles of helium
gas at 1.5 atm and 25 L,
what is the temperature?
2. How many moles of argon
gas are present in 500 mL at
3 atm and 30 ºC?
Gas Stoichiometry
• Coefficients in balanced
reaction equations are mole
ratios AND gas volume ratios!
• Can do “volume to volume”
stoichiometry when P and T
are held constant
Volume - Volume Gas Stoich
(These are just like mole to mole
problems - one conversion!)
How many liters of NH3 will be
produced if 10 liters of N2 are
consumed according to the
following reaction:
N2 (g) + 3H2 (g) -----> 2NH3 (g)
Volume-Mass Gas Stoich
Example
N2 (g) + 3H2 (g) -----> 2NH3 (g)
How many grams of hydrogen
gas are required to create 20L
of ammonia gas if the above
reaction occurs at STP?
*do volume to volume stoich,
then molar volume, then
molar mass.
Mass-Volume Gas Stoich
Example
N2 (g) + 3H2 (g) -----> 2NH3 (g)
How many liters of ammonia
gas can be created from 50
grams of nitrogen gas at
STP?
*mass to mole, mole ratio, then
molar volume