Translational Energy of Molecules and Vrms

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Homework Help Overview

The discussion revolves around calculating the average (rms) speed of molecules in a quantity of molecular hydrogen gas at a specified temperature and pressure. The context includes the application of kinetic energy equations relevant to gas behavior.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The original poster attempts to calculate the rms speed using kinetic energy equations but questions the accuracy of their result compared to a provided answer. Some participants question the rounding of the answer and the nature of the multiple-choice options presented.

Discussion Status

Participants are actively engaging with the original poster's calculations, offering insights on the nature of the answer choices and discussing whether rounding could account for the discrepancy. There is no explicit consensus on the correctness of the original calculation, but guidance is being provided regarding the multiple-choice format.

Contextual Notes

The original poster notes that the answer they calculated does not match the expected answer, which raises questions about rounding and the nature of the multiple-choice options provided in the problem.

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1. A quantity of molecular hydrogen (H2) gas fills a one liter container at a temperature of 200 K and pressure of 1 atm.

What is the average (rms) speed of the molecules?

Homework Equations



KE_trans = 1/2 M<v^2>
Energy_trans = 3/2kT = 3/2RT
H2 = 2g/mol

The Attempt at a Solution



Assuming 1 mol of H2:
mass = .002kg

1/2 M<v^2> = 3/2RT
(.002kg)<v^2> = 3R(200K)
<v^2> = 2494200m/s
Vrms = sqrt(<v^2>) = 1579.30m/s

Which is wrong.
The correct answer is 1600m/s. (Not a rounding error.)

Can anyone help me?
Thanks!
 
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The answer is certainly rounded.

ehild
 
The reason I don't believe its rounded is because the options are:
(a) 16 m/s
(b) 74 m/s
(c) 274 m/s
(d) 1600 m/s
(e) 4570 m/s

So if it were rounded it would be rounded to 1580 and in my
physics exams they always give you the exact answer or really close to it.
 
You result is correct. Do you need to present your calculation, or just have to choose one value? If it is a multi-choice question mark the closest one.

ehild
 
Yea, its a multiple choice question.
Thanks for your help!
 

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