${\mathrm{TiCl}}_4+2\mathrm{Mg}\stackrel{{850}^0\mathrm{C}}{\to } .........+...........$

When highly reactive metals such as sodium, calcium, aluminium etc are used as reducing agents.  They displace metals of lower reactivity from the compound. The displacement reactions are highly exothermic.  The amount of heat evolved is so large that the metals produced are in molten state.

${\mathrm{TiCl}}_4+2\mathrm{Mg}\stackrel{{850}^0\mathrm{C}}{\to } \mathrm{Ti}+2{\mathrm{MgCl}}_2$