Question 30 Nitrogen dioxide is a reddish-brown toxic gas has a characteristic s

Question

Question 30 Nitrogen dioxide is a reddish-brown toxic gas has a characteristic sharp, biting odour and is a prominent air pollutant. It is formed in most air-fueled combustion processes; the most prominent sources are internal combustion engines and fossl power stations. The photodissociation of nitrogen dioxide occurs in the troposphere. 2 points NO2(g) + photon NO(g) + 0(g) This reaction is a key reaction leading to the formation of tropospheric ozone. The ON-O bond energy is 306 kJ/mol. What is the longest wavelength of light, in nm, that will break this bond?

Explanation / Answer

Energy of one photon of required wavelength can be obtained as;

hv = Ephoton

h = plank's constant = 6.626 × 10-34 m2 kg / s

v = frequency

We have energy of 1 mol bonds = 306 kJ

bond energy of 1 molecule = 306 x 1000 J / (6.022 x 1023) = 5.08 x 10-19 J

5.08 x 10-19 J = hv = 6.626 × 10-34 m2 kg / s x v

v = 7.669 x 1014 /s

also c = v

= wavelength in m

v = frequency in 1/s

c = speed of light = 3 x 108 m/s

= 3 x 108 m/s / (7.669 x 1014 /s) = 3.912 x 10-7 m

= 391.2 nm

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