Answer : The mass of liquid sodium needed are, 
Explanation :
First we have to calculate the number of moles of liquid sodium.

where,
q = heat absorb = 1.20 MJ = 1.20 × 10⁶ J
n = number of moles of liquid sodium = ?
c = specific heat capacity = 
= change in temperature = 
Now put all the given values in the above formula, we get:


Now we have to calculate the mass of liquid sodium.
Molar mass of Na = 23 g/mol


Therefore, the mass of liquid sodium needed are, 
So if the sum of the enthalpies of the reactants is greater than the products, the reaction will be exothermic. If the products side has a larger enthalpy, the reaction is endothermic. You may wonder why endothermic reactions, which soak up energy or enthalpy from the environment, even happen