Modern inorganic chemistry

ENERGETICS 65

Na(s) NaCKs)

2. |H 2 (g) + iCl 2 (g) - HCl(g)
   In both reactions 1 and 2 the energy factors are favourable; pure
   sodium and chlorine do react at room temperature but hydrogen
   and chlorine are (kinetically) stable in the absence of light ; in the
   presence of light (to give the reaction additional energy) they react
   explosively to form hydrogen chloride. Since we have seen on p. 62
   that a spontaneous reaction can be endothermic (although the vast
   majority are exothermic), we must now consider the energy factor
   in more detail.
   When we say that reactions 1 and 2 'go' we actually mean that
   the equilibrium between eactants and products is displaced from
   the reactants towards the products. We represent this strictly by
   the equation (for reaction 2)

iK 2 (g) + id 2 (g) -^=- HCl(g)
By application of the Equilibrium Law, the equilibrium constants
are as given at the top of the next page.

AGf 98 ,

-150

-IOO

-50

kJmol"

-20

log, 0 K 298

10 20

—50

Slope

-5-69

—ioo

Figure 3.3. Graph o/AG 298 against log, 0 K 2