Suppose that the calorimeter shown here was used to determine the energy change for an acid-base reaction. 150.0 ml of 0.50 m hcl is added to 50.0 ml of 1.00 m naoh to make 200.0 g of solution.

The actual neutralization reaction between the acid and base is H+ + OH- = H2O and this is what the -56 kJ/mole applies to   
Then work out how much reactants you have   
0.150 L * 0.50 mole/L = 0.075 mole for HCl  
0.050 L * 1.00 mole/L = 0.050 mole for NaOH   
So the HCl is in excess and the NaOH will all react. The energy released is -56 kJ/mole * 0.050 mole = -2.8 kJ or -2800 J   
Temperature changes of solid, liquids or gas are calculated using:   
energy = mass * heat capacity * (initial temperature - final temperature)   
-2800 J = 200g * 4.18 J/gC * (53.9C - Tf)   
Tf = 57.25 C. Rounded off I would say 57.3 C