Question

Electromagnetic radiation of wavelength 242 nm is just
sufficient to ionise the sodium atom. Calculate the lonisation
energy of sodium in kJ mol-1​

Answer 1

Answer:

494.5 kJ mol⁻¹

Explanation:

Given :

Wavelength λ = 242 nm

In term of meter m :

λ = 242 × 10⁻⁹ m

We are asked to calculate ionisation energy of sodium :

We know :

E = N h ν

= > E = N h c / λ

Values of constant are :

N = 6.02 × 10²³ mol⁻¹

h = 6.626 × 10⁻³⁴ J sec

c = 3 × 10⁸ m / sec

Putting values we get :

E = ( 6.02 × 10²³ ) ( 6.626 × 10⁻³⁴ ) ( 3 × 10⁸ ) / 242 × 10⁻⁹

E = ( 6.02 × 10³¹ ) ( 6.626 × 10⁻³⁴ ) ( 3 ) / 242 × 10⁻⁹

E = ( 6.02 ) ( 6.626 × 10⁻³ ) ( 3 ) / 242 × 10⁻⁹

E = ( 18.06 × 6.626 × 10⁶ ) / 242

E = 4.945 × 10⁵ J mol⁻¹

E = 494.5 kJ mol⁻¹

Hence we get required answer.