\(\Delta U =0\)
\(\Rightarrow \frac{ F _{1}}{2} n _{1} R \Delta T +\frac{ F _{2}}{2} n _{2} R \Delta T =0\)
\(\Rightarrow \frac{ F _{1}}{2} n _{1} R \left( T _{1}- T \right)+\frac{ F _{2}}{2} n _{2} R \left( T _{2}- T \right)=0\)
\(\Rightarrow T =\frac{ F _{1} n _{1} RT _{1}+ F _{2} n _{2} RT _{2}}{ F _{1} n _{1} R + F _{2} n _{2} R } \Rightarrow \frac{ F _{1} n _{1} T _{1}+ F _{2} n _{2} T _{2}}{ F _{1} n _{1}+ F _{2} n _{2}}\)