See the calculation on this YouTube video

Solution The heat energy absorbed by the calorimeter in increasing its temperature by 1.841 K is given by

q = C ?T = 6.745 kJ K^–1 × 1.841 K = 12.42 kJ

Since this heat energy was released by the reaction system, we must regard it as negative. Accordingly,

q_V = –12.42 kJ = ?U

We need now only to calculate the change in internal energy per mole, that is, ?U_m. Now

         

Thus