From a molecular viewpoint, where does the energy absorbed in an endothermic chemical reaction go? Why does the reaction mixture undergo a decrease in temperature even though energy is absorbed?
Solution: Step1: According to Planck’s quantum theory of radiation, radiant energy is not emitted or absorbed continuously but discontinuously in the form of small packets of energy called quanta. As matter also emits and absorbs energy, it is done only in the form of some fixed quantities, i.e., it can emit or absorb energy equal to h, 2h, 3h…. or any other integral multiple of h but cannot emit or absorb energy equal to 1.6h, 3.2h or any other fractional value of h. Imagine a ladder having steps labelled as 1, 2, 3, 4, ……. from the bottom. Your position on the ladder can only be on a step and never in between. Step2: Similarly, if human height were quantized in 1 - foot increments, the, as a child grows up, his/her height would increase in “jumps” of 1 foot at a time and not continuously. Thus, the correct option is (iii). -----------------