10of molecular-kinetic theory Ideal gas Methodological guide

Methodological guide for teachers

“Chalk Talk”: The teacher will introduce the theme of gas laws and ideal gases, and will give a marker to three students.  Students with markers will go to the board and write one thing they know (or think they know) on the board.  Once they have written one thing, they will give the marker to another student.  This process will be repeated until a large amount of information is on the board.  The teacher should observe the students to make sure that each student writes at least one thing on the board.  After 5-7 minutes, the teacher will look at the board with the students and correct any mistakes.

Presentation about the gas laws (Boyle, Charles, Gay-Lussac) with demonstrations.  This presentation should be adjusted in length/detail based on the amount of prior knowledge demonstrated in the chalk talk activity.

Demonstrations—students will be shown each demonstration and 1) explain what is happening and 2) identify which gas law it is demonstrating.

Boyle: students will take a plastic syringe, and blocking the end with their thumb, will decrease the volume and observe how the pressure changes.

Charles: A balloon with a string tied to the end will be placed outside the window.  After a few minutes the balloon will be pulled back inside and students will observe the change in volume caused by the change in temperature.

Gay-Lussac: a candle will be placed in a dish with a small amount of water in the bottom.  After the candle is lit, a glass or beaker will be placed over the candle.  The water should rise up in a column as the candle extinguishes and the air inside cools.

Homework solutions and answers

2) E_k = ·k·T

E_k = ·1.38·10^-23 J/K·237 K

E_k ≈ 5.7·10^-21 J

3) υ_rms =  

υ_rms =  

υ_rms ≈ 520 m/s

1)      Assuming the same constant distance and linear distribution of molecules, we can calculate the number of molecules along 1 m line:

N (L = 1 m) =  

N = 3·

d =  

d ≈ 3· m

2)      P·V = n·R·T

n =    (M = 0.029 kg/mole)

m = ρ·V

ρ =

ρ =  

ρ ≈ 1.29 kg/m³