Question

In a calorimeter, Magnesium Chloride is dissolved in water with the following reaction: MgCl2s--Mg+2+2Cl-. The calorimeter holds 625g water. The initial temp was 20c but raises to 28c after 12.8 grams are added. What is deltaH for the chemical reaction ?

Answer 1

Since delta T is positive Q will be calculated as positive. That indicates reaction is endothermic. We are using heat to break bonds here, that's how you can keep in mind the character of the equation.

Q = m.c. delta(T)
We have 625g of water, the c of water is (4.184 J/g-C)
Delta T is 8C (T2-T1)

Q(joules) = 625. 4.184. 8