Consider the following reactions. (note: (s) = solid, (l) = liquid, and (g) = gas.)
mg(s) + ½o2(g) → mgo(s) + 146 kcal/mole
h2(g) + ½o2(g) → h2o(g), δh = -57.82 kcal/mole
the temperature of the surroundings will:

increase
decrease

how to make a simple air condition

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"