NEET UG 2022 — Chemistry Physical Chemistry

Since, the striking photon has energy equal to $h v \mathrm{v}$hvv and the minimum energy required to eject the electron is $h v_0$hv0​ (work function $\mathrm{W}_0$W0​), the difference in energy $\left(h v-h v_0\right)$(hv−hv0​) is transferred as the kinetic energy of the photoelectron. $h v=h v_0+\mathrm{KE}$hv=hv0​+KE $h v_0=$hv0​= minimum energy required to remove electron) Energy of a $300 \mathrm{~nm}$300 nm photon is given by $$\begin{aligned} & \Rightarrow \mathrm{E}=\frac{h c}{\lambda} \\ & =\frac{6.626 \times 10^{-34} \mathrm{Js} \times 3 \times 10^8 \mathrm{~ms}^{-1}}{300 \times 10^{-9} \mathrm{~m}} \\ & =6.626 \times 10^{-19} \mathrm{~J} \end{aligned}$$​⇒E=λhc​=300×10−9 m6.626×10−34Js×3×108 ms−1​=6.626×10−19 J​ Energy of one mole of photons $$\begin{aligned} & =6.626 \times 10^{-19} \mathrm{~J} \times 6.022 \times 10^{23} \mathrm{~mol}^{-1} \\ & =3.99 \times 10^5 \mathrm{~J} \mathrm{~mol}^{-1} \end{aligned}$$​=6.626×10−19 J×6.022×1023 mol−1=3.99×105 J mol−1​ The minimum energy needed to remove one mole of electrons $=(3.99-1.68) \times 10^5 \mathrm{~J} \mathrm{~mol}^{-1}$=(3.99−1.68)×105 J mol−1 $=2.31 \times 10^5 \mathrm{~J} \mathrm{~mol}^{-1}$=2.31×105 J mol−1