A particular balloon is designed by its manufacturer to be to be inflated to a volume no more than 2.5 L. If the balloon is filled with 2.0 L of Helium at sea level and 4°C, is released and rises to an altitude at which the atmospheric pressure is 500. mmHg and -4 °C, will the balloon burst?

I'm having trouble understanding gas law. Do I use the PV=NRT formula?

Also....please help me understand the Calorimetry math for the question below.

A student masses 5.34 g of NH4Cl, and adds it to a calorimeter containing 100.0 mL of water at 21.0 oC. As the salt dissolves, the temperature drops to 17.6 oC. Calculate the ΔHsol of ammonium chloride in kJ/mol. Is the process endothermic or exothermic? Explain. Density of water 1.00g/mL. Specific heat of water = 4.184 J/g oC