Question

18-31. In formaldehyde, the transition n S p*(T1) occurs at 397 nm, and the n S p*(S1) transition comes at 355 nm. What is the differ- ence in energy (kJ/mol) between the S1 and T1 states? This differ- ence is due to the different electron spins in the two states.

Answer 1

The difference in energy between the
`S_1` and
`T_1` states is 35.7 kJ/mol.

Step-by-step explanation:

The Planck's equation :

`E=(hc)/(\lambda)`

Where:

E = Energy of the electromagnetic radiations.

h = Planck's constant =
`6.626* 10^(-34) Js`

c = speed of light =
`3* 10^8 m/s`

`\lambda` = Wavelength of the electromagnetic radiations.

Energy associated with
`T_1` transition :
`E_1`

Wavelength associated with
`T_1` transition :

`\lambda _1=397 nm=397* 10^(-9) m`

Energy associated with
`S_1` transition :
`E_2`

Wavelength associated with
`S_1` transition :
`\lambda _2=355 nm=355* 10^(-9) m`

The difference in energy between the
`S_1` and
`T_1` states:

`E=E_1-E_2=(hc)/(\lambda _2)-(hc)/(\lambda _1)`

`E=hc* ((1)/(\lambda _2)-(1)/(\lambda _1))`

`E=6.626* 10^(-34) Js * 3* 10^8 m/s((1)/(355* 10^(-9)m)-(1)/(397* 10^(-9) m))`

`E=5.92* 10^(-20) J`

1 J = 0.001 kJ

`E=5.92* 10^(-20)* 10^(-3) kJ=5.92* 10^(-23) kJ`

1 mole =
`6.022* 10^(-23)`

The difference in energy(kJ/mol) between the
`S_1` and
`T_1` states:

`=5.92* 10^(-23) kJ* 6.022* 10^(23) mol^(-1)=35.7 kJ/mol`