First, the balanced chemical equation of the reaction must be written. This gives:
2 AgNO3 (aq) + CaCl2 (aq) --> 2 AgCl (s) + Ca(NO3)2 (aq)
This shows that for every mole of CaCl2, 2 moles of AgNO3 reacts (1:2 ratio). Given the volume and molarity of CaCl2, we can compute for the number of moles of CaCl2.
moles CaCl2 = 1.5M(25mL/1000) = 0.0375 moles
Now, we can also compute for the moles of AgNO3 using the balanced equation.
moles AgNO3 = 2(0.0375) = 0.075 moles
Using the moles and molarity of AgNO3, we can compute for the volume needed.
volume (mL)/1000 = 0.075/0.5 = 150 mL of silver nitrate solution is required.