Question

Gaseous BF3 and BCl3 are mixed in equal molar amounts. All B-F bonds have about the same bond enthalpy, as do all B-Cl bonds. Compare the numbers of microstates to explain why the mixture tends to react to form BF2Cl(g) and BCl2F(g

Answer 1

`$BF_3 (g) + BCl_3 (g) \rightarrow BF_2 Cl + BCl_F(g)$`

Explanation 1 :

Spontaneity of the reaction is based on two factors :

-- the tendency to acquire a state of minimum energy

-- the energy of a system to acquire a maximum randomness.

Now, since there isn't much difference in the bond enthalpies of B-F and B-Cl. So, we can say the major driving factor is tendency to acquire a state of maximum randomness.

Explanation 2 :

A system containing the
`\text{` B halides has a
`\text{greater entropy}` than a system of
`$BCl_3$` and
`BF_3`.

It has the same number of
`\text{gas phase molecules}`, but more distinguishable kinds of
`\text{molecules}`, hence, more microstates and higher entropy.