Understanding KMT using Gas Properties and States of Matter

Learning Goals: Students will be able to describe matter in terms of particle motion. The description should include•Diagrams to support the description. •How the particle mass and temperature affect the image. •How the size and speed of gas particles relate to everyday objects•What are the differences and similarities between solid, liquid and gas particle motion

What is KMT?1. Gases are composed of a large number of particles that behave like hard,

spherical objects in a state of constant, random motion.

2. These particles move in a straight line until they collide with another particle or the walls of the container.

3. These particles are much smaller than the distance between particles. Most of the volume of a gas is therefore empty space.

4. There is no force of attraction between gas particles or between the particles and the walls of the container.

5. Collisions between gas particles or collisions with the walls of the container are perfectly elastic. None of the energy of a gas particle is lost when it collides with another particle or with the walls of the container.

6. The average kinetic energy of a collection of gas particles depends on the temperature of the gas and nothing else.

If you have a bottle with Helium & Nitrogen at room temperature, how do the speed of the particles compare?

A. All have same speed

B. The average speeds are the same

C. Helium particles have greater average speed

D. Nitrogen particles have greater average speed

Light and heavy gas at same temperature 300K

Speed of each particle varies!!

What happens if you add energy using the heater?

A. All atoms speed up B. All atoms speed up about the

sameC. The lighter ones speed up

moreD. The heavier ones speed up

more

answer

Which is most likely oxygen gas?

A B C

Which is most likely liquid water?

A B C

Explain what happens to the behavior of the gas particles when volume is

decreased and why.

• Speed? Why?

• Temp? Why?

• Pressure? Why?

The total KE of a substance is equal to the thermal energy of the substance.

• Predict: What happens to the temperature when molecules speed up?

• Predict: What happens to the temperature when more molecules are added?

• Do the results seem reasonable? • Tub of hot water vs glass of hot water…• What might thermal equilibrium mean in terms

of the gas and the thermometer?• What indirect measurement is a good indicator of

the thermal energy of a substance?

System Examples

• Open: Matter and energy exchanges w/ environment.

• Closed: Energy exchanges w/ environment.

• Isolated: No exchanges at all w/ environment.

• http://chemwiki.ucdavis.edu/Physical_Chemistry/Thermodynamics/A_System_And_Its_Surroundings

Why do we use the Kelvin scale to measure temperature in

thermodynamics?

• What is the definition of cold?

• What is the definition of hot?

• Which is hotter, book or box?

• What comprised “the system” in the Gas Properties simulation?

• Did energy enter or leave this system? Proof?

Question:Which graph best represents the relationship between the average kinetic energy (Kavg) of the

random motion of the molecules of an ideal gas and its absolute temperature (T)? Hint: Consider the Eqn.

Answer: (2) since Kavg is a linear function of absolute temperature T.

Temp is directly related to average KE of motion of the molecules in a sample.

𝐾𝐸𝐴𝑣𝑔 =3

2𝑘𝑇 = 1/2𝑚𝑣2

• Internal energy is the sum of the KE of all atoms or:

ETh= 𝑈 =3

2𝑁𝑘𝑇 𝑜𝑟

3

2𝑛𝑅𝑇

R = 8.31 J/mol·KkB = 1.38 x 10 -23 J/K

The temperature of air in the upper atmosphere is hot. could you get

burned from this?

KMT summary:

• Matter is made up of particles having negligible mass are in constant random motion (vibrate, rotate, translate)

• The particles are separated by great distances

• The particles collide perfectly elastically (there are no forces acting except during the collision)

• The temperature of a substance is related to the molecular velocity.

• Thermal energy is often transferred via a collision.

What are the two ways to add or remove energy from a closed system?

(Ideal Gas)