Homework Help: CHEM

Posted by K on Monday, November 5, 2007 at 10:14pm.

I just have a couple of questions that I need some help with:

1) A 0.22-caliber handgun fires a 27g bullet at a velocity of 765m/s.

Calculate the de Broglie wavelength of the bullet.

Express your answer using two significant figures in meters.

~and~

2) An X-ray photon of wavelength 0.970nm strikes a surface. The emitted electron has a kinetic energy of 956eV.

What is the binding energy of the electron in kJ/mol?
KE=1/2mv^2; 1 electron volt (eV)=1.602*10^-19J

Answer= BEmol = _______kJ/mol

please help if possible.

CHEM - Anonymous, Monday, November 5, 2007 at 10:27pm
Didn't we work a De Broglie wavelength problem for you last night? What do you think you should do or do you have an answer you would like for us to check?
- CHEM - Anonymous, Monday, November 5, 2007 at 10:28pm
  I'm not annonymous. I don't know how that name got there.
  - CHEM - DrBob222, Monday, November 5, 2007 at 10:28pm
    I'll get it right eventually.
CHEM - K, Monday, November 5, 2007 at 10:47pm
the answer came to 3.2*10^-35m. I kept typing the values into the calculator wrong. I multiplied the 765m/s, rather than dividing.

I still don't understand the other question though. Q#2.
CHEM - DrBob222, Monday, November 5, 2007 at 11:01pm
#1 is ok.
#2. I assume binding energy is the same as work function.
K. E. = (hc/lambda) - work function
Convert 956 ev to Joules and substitute for K. E.
h, c, and lambda (don't forget lambda is in meters). Solve for work function.
Check my thinking. Check for typos.
CHEM - K, Monday, November 5, 2007 at 11:13pm
Soooo???

KE = hc/lambda - 1.602*10^-19J*956eV??

6.6261*10^-34*3.0*10^8 / 9.7*10^-10m minus 1.53*10^-16??

=5.19*10^-17??? That can' be right??
- CHEM - DrBob222, Monday, November 5, 2007 at 11:21pm
  I have 5.18 instead of 5.19.
  - CHEM - K, Monday, November 5, 2007 at 11:27pm
    apparently 5.18*10^-17 kJ/mol isn't the correct answer either.
  - CHEM - K, Monday, November 5, 2007 at 11:29pm
    where am I going wrong?
CHEM - DrBob222, Monday, November 5, 2007 at 11:40pm
The answer 5.18 x 10^-17 is J/photon. You will need to change that to kJ/mol since the problem wants kJ/mol. Let me know if that isn't ok.
- CHEM - K, Monday, November 5, 2007 at 11:41pm
  so just divide by 1000? I tried that when I had 5.19*10^-20 & it told me I was incorrect?
  or did you mean to divide somewhere else along the way?
  - CHEM - DrBob222, Monday, November 5, 2007 at 11:46pm
    Divide by 1000 (1 kJ/1000 J) and multiply by 6.02 x 10^23 (6.02 x 10^23 photons/mol).
    - CHEM - K, Monday, November 5, 2007 at 11:50pm
      WOOO! 3.12*10^4 came to be correct indeed! Thank you ever so much for your time & patience.
      - CHEM - DrBob222, Monday, November 5, 2007 at 11:53pm
        So binding energy in your problem IS the same as work function which is the assumption I made in my first post. I've not heard it called that.
        
        CHEM - DrBob222, Monday, November 5, 2007 at 11:54pm
        And thanks for letting me know.
CHEM - ABU EL 3BED, Tuesday, March 26, 2013 at 12:13pm
FUUUUKKKK CHEM

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