How much heat is released when 35kg of water freezes?

You need an additional point of data here: the enthalpy of fusion, or conversely the enthalpy of melting (they differ only by their sign). For water (or ice) that value is gotten from sources such as the internet

ΔH°(fus) = 6.01 kJ/mole 

Since you have 35 000g, how many moles do you have? 
Moles H2O = 35000 g/(18.015 g/mole) = 1942.8 moles

So, take that ΔH°(fus) in kJ/mole, multiply by the number of moles, and there ya go! 

6.01 x 1942.8 = 11,676 kJ of energy is released

Hope I helped!! xx