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KMT and Ideal vs. Real Gases
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KMT and Real vs. Ideal Gases
College Chemistry Regents Review
Components of the KMT
What is the KMT?
The Kinetic Molecular Theory, or the KMT, is a way of describing the movement and behavior of gases.
KMT
1. Gases move in a constant, random, straight-line motion
2. When gases collide, the collisions are described as elastic, where no net energy is lost
3. Gases are very spread out, so volume is almost irrelevant when describing them
4. Gases have no attraction or repulsion for each other
HOWEVER, IT IS VERY RARE FOR GASES TO ALWAYS OBEY THESE LAWS
There are 4 measurements we commonly use to describe gases
1. Volume (Usually mL or L)
2. Temperature (Measured using Kelvin Scale)
3. Pressure (atm, kPa, torr, mmHg, inches of Hg, bars, millibars)
4. Moles
Ideal and Real Gases
Ideal Gases
Ideal gases follow the laws of the KMT, or the 4 descriptions that were just listed
Under standard conditions, only Hydrogen and Helium are ideal due to their small size
If gases are not "ideal", then they can be identified as "real"
Ideal Gases
Real Gases
Real Gases consist of every element (except H and He) under standard pressure
Real gases do not follow the 4 laws of the KMT
They have volumes that are too important to be ignored
They do have attraction and repulsion for each other
Can a real gas become ideal?
Is it possible for real gases to behave ideally?
Under High Temperature and Low Pressure, a Real Gas can become Ideal
The Combined Gas Law allows us to solve for an unknown measurement
P1V1 P2V2
P: Pressure
V: Volume
T: Temperature
_______ = _______ T1 T2
Combined Gas Law
The Combined Gas Law can be rewritten when one variable is constant
Charles Law Gay-Lussacs Law Boyles Law
When Pres. is constant When Volume is constant When Temp. is constant
What happens when a variable is held constant?
So, how well did you do?
Whiteboard Game Review Questions
Which of the following is NOT used when describing gases?
1.
a. Temperature
b. Heat (Joules)
c. Moles
d. Pressure
B
Also, keep track of how many questions you get right
Identify TWO parts of the Kinetic Molecular Theory (KMT)
2.
Possible Answers:
- Gases move in a constant, random, straight-line motion
- When gases collide, the collisions are described as elastic, where no net energy is lost
- Gases are very spread out, so volume is almost irrelevant when describing them
- Gases have no attraction or repulsion for each other
Which of the following is a real gas?
D
3.
a. Helium (273 K and 101.3 kPa)
b. Hydrogen
c. Oxygen (350 K and 64 kPa)
d. Argon (273 K and 101.3 kPa)
At constant temperature, what is the relationship between pressure and volume?
4.
C
a. V=(constant)P
b. P=(constant)v
c. PV=constant
d. VIP=constant
A 2.5 liter sample of gas is at STP. When the temperature is raised to 273°C and pressure is kept constant, the new volume of the gas will be
a. 1.25 L
b. 2.5 L
c. 5.0 L
d. 10.0 L
5.
C
Which changes in pressure and temperature occur as a given mass of a gas at 0.5 atm and 546 K is changed to STP?
a. The pressure is doubled and the temperature is halved
b. The pressure is doubled and the temperature is doubled
c. The pressure is halved and the temperature is halved
d. The pressure is halved and the temperature is doubled
A
6.
A gas at STP has a volume of 1.0 liter. If the pressure is doubled and the temperature remains constant, the new volume of the gas will be
a. 0.25 L
b. 2.0 L
c. 0.5 L
d. 4.0 L
C
7.
Under which conditions will the volume of a given sample of a gas always decrease?
a. Decreased pressure and decreased temperature
b. decreased pressure and increased temperature
c. increased pressure and decreased temperature
d. increased pressure and increased temperature
8.
C
What volume will a 300.0 mL sample of a gas at STP occupy when the pressure is doubled at constant temperature?
a. 150.0 mL
b. 600.0 mL
c. 2000. mL
d. 4000 mL
9.
A
A gas occupies a volume of 500. mL at a pressure of 380. torr and a temperature of 298 K. At what temperature will the gas occupy a volume of 250. mL and have a pressure of 760 torr.
a. 149 K
b. 298 K
c. 447 K
d. 596 K
10.
B