Calculate the energy required to excite one litre of hydrogen gas at 1atm and 298 K to the first excited state of atomic hydrogen. The energy for the dissociation of H-H bond is 436 kJ/ mole

$n=\frac{PV}{RT}=\frac{1\times 1}{0.0821\times 298}=0.0408mole$

Energy required for the given moles of H2 to dissociate into atoms = 0.0408 x 436 = 17.89 kJ
Total energy required for first excitation
= Energy for dissociate + Energy for excitation
$=17.89+[Rhc{\left(1\right)}^2(\frac{1}{1^2}-\frac{1}{2^2})\times 0.0408\times 6.023\times {10}^{23}\times {10}^{-3}]$$=17.89+80.35=98.24kJ$