Chapter 7, Problem 7.6E

The production of nitrogen gas for automobile airbags takes advantage of the following chemical reaction:

${\text{4NaN}}_{\text{3}}\left(\text{s}\right)+{\text{O}}_{\text{2}}\left(\text{g}\right)\to {\text{6N}}_{\text{2}}\left(\text{g}\right)+{\text{2Na}}_{\text{2}}\text{O}\left(\text{s}\right)$

If this reaction were in equilibrium, how many degrees of freedom would be necessary to describe the system?