First slide

Electromagnetic radiation and spectra

Question

One molecule of a substance absorbs one quantum of energy. The energy involved when 1.5 mole of the substance absorbs red light of frequency $7.5 \times 10^{14} \sec^{- 1}$ will be

Moderate

A

$2 .99 \times 10^{5} J$
B

$3 .23 \times 10^{5} J$
C

$4 .48 \times 10^{5} J$
D

$2 .99 \times 10^{6} J$

Solution

$\begin{array}{l} For one molecule = E = hv \\ \begin{aligned} For 1.5 moles = E & = 1.5 \times 6.023 \times 10^{23} \times hv \\ = 1.5 \times 6.023 \times 10^{23} \times 6.626 \times 10^{- 34} \times 7.5 \times 10^{14} \\ = 4.48 \times 10^{5} J \end{aligned} \end{array}$

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