- #1

tahmidbro

- 15

- 1

- Homework Statement
- a) what is the rms speed of four hydrogen molecules with the speeds of 890, 755, 902, 866m/s?

Ans : 855m/s

My problem is part b)

b) at what temperature would these hydrogen molecules be?

( Mass of H atom = 1.67 x 10^(-27) kg )

Now, in 1/2m<c^2> = (3/2)kt, should I use the mass for only 1 hydrogen atom, or mass of 2 hydrogen atoms, or the mass for all 8 atoms in 4 molecules?

- Relevant Equations
- 1/2m<c^2> = 3/2kT

the answer in the solution book is 29K which only comes if I use mass for only one atom. ( They did not show any working )

My attempt:

1/2 x (1.67 x 10^(-27)) x (355)^(2) = 3/2 x 1.38 x 10^(-23) x T

T = 29.48820652 K

The confusion arises when I tried the following question:

Q. Estimate the rms speed of the molecules of air in this room.

The answer given in the solution book :

Estimate of 20 °C (T = 293 K); assume all molecules are dinitrogen, so m = 4.676 × 10^(–26) kg; gives rms = 509m/s.

which is only possible if I use mass of two nitrogen atoms.

Please help :-)

My attempt:

1/2 x (1.67 x 10^(-27)) x (355)^(2) = 3/2 x 1.38 x 10^(-23) x T

T = 29.48820652 K

The confusion arises when I tried the following question:

Q. Estimate the rms speed of the molecules of air in this room.

The answer given in the solution book :

Estimate of 20 °C (T = 293 K); assume all molecules are dinitrogen, so m = 4.676 × 10^(–26) kg; gives rms = 509m/s.

which is only possible if I use mass of two nitrogen atoms.

Please help :-)