as the randomness increases , that becomes the driving force for the reaction
If there is a reaction involving the heating of a substance, heat gained by solution= Q=mc∆T, where m is the mass of the substance, c is the specific heat capacity of the substance, and ∆T the change in temperature. ∆H is determined through ∆H= Q/n, where n is the number of moles of
the substance. In this case, as it involves heating, bonds are being broken due to the rise in temperature, giving the derived ∆H a negative value.
Likewise, if the reaction involves the heating of the substance, there would be a temperature rise, and this means that energy is transferred from the flame to the substance. There would be a higher amount of kinetic energy in the system, resulting in more ways for the energy to be distributed amongst the particles, giving rise to greater disorder. Thus ∆S increases.
As for the second part of your question, as the Cl-Cl bond is being formed from its atoms, this reaction is likely to be exothermic as heat needs to be given out in order to form bonds.
