Thermodynamics Questions for Helium and Flourine

[Tofuphysics]

Hey all, I just discrovered these forums, thankoodness, because I'm taking physics over the summer (its a requirement at my school), and not being a science-y person, I really need help.

Homework Statement

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This is the problem:

Problem 1
a. What is the average translational kinetic energy of a helium atom at 300 K?
b. What is the average translational velocity of a helium atom at 300 K?
c. What is the total internal energy of a 4.0 g sample of He at 300 K?
d. What is the total internal energy of a 4.0 g sample of He at 301 K?
e. How much energy is needed to raise the temperature of 4.0 g of He by one degree K?

And then the next problem is he same cocept, but with Flourine (F2)

Problem 2
a. What is the average translational kinetic energy of a F2 molceule at 300 K?
b. What is the average translational velocity of a F2 moelcule at 300 K?
c. What is the total internal energy of a 38 g sample of F2 at 300 K?
d. What is the total internal energy of a 38 g sample of F2 at 301 K?
e. How much energy is needed to raise the temperature of 38 g of F2 by one degree K?

Homework Equations

KE=(3/2)(Kb)(T)
KE=1/2mv^2
Avogadroes number= 6.02 x 10^-23
1 MW= 1x wx^6 w (i don't know what this means but the teacher wrote it on the board)

The Attempt at a Solution

I think that you have to use the KE equations and the molar mass (which you can figure out using the periodic table?) but I'm really not sure how to put it together.


Thankyou so much if you had the patience to read all that!
-Tofuphysics

 

[Hootenanny]

Welcome to PF Tofuphysics,

KE=(3/2)(Kb)(T)
KE=1/2mv^2
Avogadroes number= 6.02 x 10^-23

Assuming of course that you are treating these gases as ideal, then those equations are correct and will certainly allow you to answer questions (a) and (b) in each case. However, a third equation would be infinitely more useful in answering the remaining parts.

 

[Moetasim]

Hello Tofuphysics,

I'm glad you found these forums to help you with your physics homework! Let's go through the questions one by one and see if we can figure out the answers together.

a. The average translational kinetic energy of a helium atom at 300 K can be calculated using the equation KE=(3/2)(Kb)(T). Kb represents the Boltzmann constant, which is equal to 1.38x10^-23 J/K. T is the temperature in Kelvin, so for 300 K, we get:

KE = (3/2)(1.38x10^-23 J/K)(300 K) = 6.21x10^-21 J

b. To find the average translational velocity of a helium atom, we can use the equation KE=1/2mv^2. Rearranging this equation, we get v = √(2KE/m). Plugging in the value for KE from part a and the mass of a helium atom (4.0 g/mol), we get:

v = √(2(6.21x10^-21 J)/(4.0 g/mol)) = 8.77x10^2 m/s

c. The total internal energy of a 4.0 g sample of He at 300 K can be calculated by multiplying the average translational kinetic energy from part a by the number of atoms in the sample. The molar mass of He is 4.0 g/mol, so there are 1 mol of atoms in 4.0 g of He. Using Avogadro's number (6.02x10^23 atoms/mol), we get:

Total internal energy = (6.21x10^-21 J/atom)(6.02x10^23 atoms/mol) = 3.74x10^3 J

d. To find the total internal energy of a 4.0 g sample of He at 301 K, we can use the same method as in part c, but with the new average translational kinetic energy at 301 K. This value can be calculated using the equation KE=(3/2)(Kb)(T) as in part a. The total internal energy at 301 K will be slightly higher than at 300 K.

e. The amount of energy needed to raise the temperature of 4.0 g of He by one degree K can be