Chem 170 Chapter 7

Question 1

Calculate the energy of the green light emitted, per photon, by a mercury lamp with a frequency of 5.49 × 1014 Hz.

Answer 1

E = h v

h, planck’s constant = 6.626x10^-34 J s

v = 5.49 x 10^14 s^-1 (the SI unit of frequency (s^-1) is Hertz

E = 6.626x10^-34 J s x (5.49 x 10^14 s^-1) = 3.64x10^-19 J/photon

3.64 × 10-19 J

Question 2

When waves of equal amplitude from two sources are out of phase when they interact, it is called:

Answer 2

destructive interference.

Question 3

The vertical height of a wave is called:

Answer 3

amplitude.

Question 4

How many different values of (l ) are possible in the third principal level?

Answer 4

3 (0,1,2)

Question 5

Which quantum numbers describes the shape of an orbital?

Answer 5

(L) angular momentum quantum number

Question 6

Calculate the wavelength (in nm) of the blue light emitted by a mercury lamp with a frequency of 6.88 × 1014 Hz.

Answer 6

436 nm

f=c/λ (frequency = speed/wavelength) 
re-arrange this: 
λ=c/f 
λ=3x10^8(the speed of light)/6.88x10^14 
λ=4.36x10^-7m or 436nm

Question 7

Calculate the wavelength of an electron (m = 9.11 × 10-28 g) moving at 3.66 × 106 m/s.

Answer 7

1.99 × 10^-10 m

Wavelength = h/mv

De Broglies wavelength Formula

wavelength = (6.626x10^-24)/( 9.11 x 10^-31kg x 3.66 x 10^6) = 1.98 x 10^-10m

Question 8

Calculate the energy of the red light emitted by a neon atom with a wavelength of 703.2 nm.

Answer 8

2.83 × 10-19 J

where h is Planck’s constant (h = 6.6*10^(-34) Js) and
f the frequency of the wave. Since f = c / lambda (lambda is the wavelength), you have

E = h * c / lambda = 6.610^(-34) * 310^8 m/s / 703.2 * 10^-9 m = 2.82 * 10^(-19) J