Need help.. i have tried my best to solve this problem but i just can't seem to find to right answer?

Question

How much heat is released when 9.16 grams of solid calcium hydroxide is added to 293 mL of 7.5 M HNO3?

Answer 1

You're going to need some information that you haven't given in this problem to get to the final answer, but let's work toward that.

First, calculate the number of moles of Ca(OH)2 that you're beginning with by dividing 9.16 grams by the molar mass of Ca(OH)2. Just to be safe, calculate also the number of moles of HNO3 that you're beginning with by multiplying the molarity of your HNO3 solution by the volume (in L).

When you do that you'll find that you have many more moles of HNO3 than you do Ca(OH)2, and so the calcium hydroxide is the limiting reactant.

When you add solid Ca(OH)2 to aqueous HNO3, the net ionic equation of the reaction occurring is:

Ca(OH)2(s) + 2 H+(aq) --> Ca2+(aq) + 2 H2O(l)

I'm guessing that you have a table of enthalpy of formation values for compounds and ions. Just add up the enthalpies of formation of each of the products (multiplying by 2 when needed) and subtract the sum of the enthalpies of formation of the products. That value will be the amount of heat released by 1 mole of calcium hydroxide.

Just multiply that value by the number of moles of Ca(OH)2 that you started with, and you've got it.

Hope this helps...