Gases, Their Properties and the Kinetic Molecular Theory

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Dale Phillips
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1 Up to this point of the school year we have covered mostly just two of the four states of matter we mentioned at the beginning. Those, of course, are solids and liquids. While plasmas are pretty neat, we can not achieve having a plasma in our laboratory. So the last state of matter we will cover is GASES.

2 Up to this point of the school year we have covered mostly just two of the four states of matter we mentioned at the beginning. Those, of course, are solids and liquids. While plasmas are pretty neat, we can not achieve having a plasma in our laboratory. So the last state of matter we will cover is GASES. Gases are the least complex state of matter. In elementary school you learned that gases:

3 Up to this point of the school year we have covered mostly just two of the four states of matter we mentioned at the beginning. Those, of course, are solids and liquids. While plasmas are pretty neat, we can not achieve having a plasma in our laboratory. So the last state of matter we will cover is GASES. Gases are the least complex state of matter. In elementary school you learned that gases: have neither a fixed shape nor a fixed volume. will expand to fill its container completely.

4 Up to this point of the school year we have covered mostly just two of the four states of matter we mentioned at the beginning. Those, of course, are solids and liquids. While plasmas are pretty neat, we can not achieve having a plasma in our laboratory. So the last state of matter we will cover is GASES. Gases are the least complex state of matter. In elementary school you learned that gases: have neither a fixed shape nor a fixed volume. will expand to fill its container completely. In fact the particles in gases are not neatly arranged, and they don't even touch each other most of the time. There is lots of space in between particles, which is why when put in a container, it is filled with the gas. And when released from a container, the gas is dispersed.

5 Up to this point of the school year we have covered mostly just two of the four states of matter we mentioned at the beginning. Those, of course, are solids and liquids. While plasmas are pretty neat, we can not achieve having a plasma in our laboratory. So the last state of matter we will cover is GASES. Gases are the least complex state of matter. In elementary school you learned that gases: have neither a fixed shape nor a fixed volume. will expand to fill its container completely. But something else that you should remember from our discussion earlier in the year is that gases:

6 Up to this point of the school year we have covered mostly just two of the four states of matter we mentioned at the beginning. Those, of course, are solids and liquids. While plasmas are pretty neat, we can not achieve having a plasma in our laboratory. So the last state of matter we will cover is GASES. Gases are the least complex state of matter. In elementary school you learned that gases: have neither a fixed shape nor a fixed volume. will expand to fill its container completely. But something else that you should remember from our discussion earlier in the year is that gases: have molecules that are always in motion. are compressible. can have variable densities.

7 Now when we cover gases this chapter we will use what is known as the, or KMT, to describe their behavior. Developed in the mid-1800s, by Boltzmann and Maxwell, the is still extremely useful. This theory is based upon assumptions about a theoretical gas, often referred to as the ideal gas.

8 Now when we cover gases this chapter, we will use what is known as the Kinetic Molecular Theory, or KMT, to describe their behavior. Developed in the mid-1800s, by Boltzmann and Maxwell, the is still extremely useful. This theory is based upon assumptions about a theoretical gas, often referred to as the ideal gas. Assumptions made by the :

9 Now when we cover gases this chapter, we will use what is known as the Kinetic Molecular Theory, or KMT, to describe their behavior. Developed in the mid-1800s, by Boltzmann and Maxwell, the is still extremely useful. This theory is based upon assumptions about a theoretical gas, often referred to as the ideal gas. Assumptions made by the : 1. The molecules of an ideal gas are considered to be dimensionless points that have no volume. ie. Molecular volume is so small in comparison to the total volume of the gas in its container thus the molecular volume is ignored in most gas calculations.

10 Now when we cover gases this chapter, we will use what is known as the Kinetic Molecular Theory, or KMT, to describe their behavior. Developed in the mid-1800s, by Boltzmann and Maxwell, the is still extremely useful. This theory is based upon assumptions about a theoretical gas, often referred to as the ideal gas. Assumptions made by the : 1. The molecules of an ideal gas are considered to be dimensionless points that have no volume. ie. Molecular volume is so small in comparison to the total volume of the gas in its container thus the molecular volume is ignored in most gas calculations. 2. The molecules of a gas are in constant straight-line motion. ie. The only time this motion is disturbed is when gas molecules collide together.

11 Now when we cover gases this chapter, we will use what is known as the Kinetic Molecular Theory, or KMT, to describe their behavior. Developed in the mid-1800s, by Boltzmann and Maxwell, the is still extremely useful. This theory is based upon assumptions about a theoretical gas, often referred to as the ideal gas. Assumptions made by the : 1. The molecules of an ideal gas are considered to be dimensionless points that have no volume. ie. Molecular volume is so small in comparison to the total volume of the gas in its container thus the molecular volume is ignored in most gas calculations. 2. The molecules of a gas are in constant straight-line motion. ie. The only time this motion is disturbed is when gas molecules collide together. 3. The collisions that occur between molecules are perfectly elastic. ie. No energy is lost or gained when gas molecules collide.

12 Now when we cover gases this chapter, we will use what is known as the Kinetic Molecular Theory, or KMT, to describe their behavior. Developed in the mid-1800s, by Boltzmann and Maxwell, the is still extremely useful. This theory is based upon assumptions about a theoretical gas, often referred to as the ideal gas. Assumptions made by the : 1. The molecules of an ideal gas are considered to be dimensionless points that have no volume. ie. Molecular volume is so small in comparison to the total volume of the gas in its container thus the molecular volume is ignored in most gas calculations. 2. The molecules of a gas are in constant straight-line motion. ie. The only time this motion is disturbed is when gas molecules collide together. 3. The collisions that occur between molecules are perfectly elastic. ie. No energy is lost or gained when gas molecules collide. 4. The molecules of an ideal gas do not exert any attractive forces on each other. ie. If there were attractions between the molecules, they would eventually bunch together and the pressure would decrease.

13 Now when we cover gases this chapter, we will use what is known as the Kinetic Molecular Theory, or KMT, to describe their behavior. Developed in the mid-1800s, by Boltzmann and Maxwell, the is still extremely useful. This theory is based upon assumptions about a theoretical gas, often referred to as the ideal gas. Assumptions made by the : 1. The molecules of an ideal gas are considered to be dimensionless points that have no volume. ie. Molecular volume is so small in comparison to the total volume of the gas in its container thus the molecular volume is ignored in most gas calculations. 2. The molecules of a gas are in constant straight-line motion. ie. The only time this motion is disturbed is when gas molecules collide together. 3. The collisions that occur between molecules are perfectly elastic. ie. No energy is lost or gained when gas molecules collide. 4. The molecules of an ideal gas do not exert any attractive forces on each other. ie. If there were attractions between the molecules, they would eventually bunch together and the pressure would decrease. 5. The average kinetic energy of the molecules is directly proportional to the absolute temperature.

14 But do real gases act as ideal gases? And if so when?

15 But do real gases act as ideal gases? And if so when? The main flaw in the ideal gas model is the assumption that gas molecules do not attract or repel each other. Attractions and repulsion's are negligible when the distance between molecules is large, but they do become larger as the molecules become closer together. If you can contrive conditions that force the molecules into close contact, so that attractions and repulsion's can't be neglected, you will likely see deviations from ideal behavior.

16 But do real gases act as ideal gases? And if so when? The main flaw in the ideal gas model is the assumption that gas molecules do not attract or repel each other. Attractions and repulsion's are negligible when the distance between molecules is large, but they do become larger as the molecules become closer together. If you can contrive conditions that force the molecules into close contact, so that attractions and repulsion's can't be neglected, you will likely see deviations from ideal behavior. SO decreasing the pressure and/or increasing the temperature will cause the molecules to move farther apart on average. That should cause the gas to behave more ideally.

17 This brings us to the variables that we will use to describe ALL gaseous systems:

18 This brings us to the variables that we will use to describe ALL gaseous systems: Volume (V) - the amount of space that the gas occupies, usually measured in Liters, but can be in ml, cm3 or even m3.

19 This brings us to the variables that we will use to describe ALL gaseous systems: Volume (V) - the amount of space that the gas occupies, usually measured in Liters, but can be in ml, cm3 or even m3. Temperature (T) - the measure of the average kinetic energy of the molecules, usually measured in C but must be converted into Kelvin (K). Remember K = C + 273

20 This brings us to the variables that we will use to describe ALL gaseous systems: Volume (V) - the amount of space that the gas occupies, usually measured in Liters, but can be in ml, cm3 or even m3. Temperature (T) - the measure of the average kinetic energy of the molecules, usually measured in C but must be converted into Kelvin (K). Remember K = C Amount of gas (n) - the number of moles of gas present.

21 This brings us to the variables that we will use to describe ALL gaseous systems: Volume (V) - the amount of space that the gas occupies, usually measured in Liters, but can be in ml, cm3 or even m3. Temperature (T) - the measure of the average kinetic energy of the molecules, usually measured in C but must be converted into Kelvin (K). Remember K = C Amount of gas (n) - the number of moles of gas present. Pressure (P) - the force per unit area exerted by a gas within a system. While the English system uses psi, we will use Pascals, (Pa), kilopascals (kpa) or atmosphere (atm).

22 Often when we refer to gases we will say that they may exist at STP.

23 Often when we refer to gases we will say that they may exist at STP. STP stands for Standard Temperature & Pressure and always has the same variables.

24 Often when we refer to gases we will say that they may exist at STP. STP stands for Standard Temperature & Pressure and always has the same variables. Standard Temperature is 0 C or 273 K. Standard Pressure is 1 atm or kpa.

25 Check for understanding: 1. Give two physical properties that clearly distinguish gases from liquids or solids. 2. List three ways that an ideal gas differs from a real gas. 3. Describe the relationship between molecular energy and temperature. 4. What are the four variable discussed in this section that can be used to describe a gas quantitatively and what are some units for each?

Gases! n Properties! n Kinetic Molecular Theory! n Variables! n The Atmosphere! n Gas Laws!

Gases! n Properties! n Kinetic Molecular Theory! n Variables! n The Atmosphere! n Gas Laws! Gases n Properties n Kinetic Molecular Theory n Variables n The Atmosphere n Gas Laws Properties of a Gas n No definite shape or volume n Gases expand to fill any container n Thus they take the shape of