Heat of Formation: Is Q Always Positive?

[angelababyy]

Homework Statement

When using the equation, Q=ms∆T, is the heat always positive?

Homework Equations

heat of formation = q/mol (but of course the moles used in this lab is a positive number)

The Attempt at a Solution

I'm working on the energy of magnesium lab where magnesium ribbon contacts and reacts with hydrochloric acid. The theoretical heat of formation is -461.96 kJ/mol, but I got 386.1 kJ/mol of Mg as the largest amount (I'm turning in three trials).
m & s are given as 100 g and 4.184 J/g Celsius respectively. Therefore, the only variable that would make the energy negative would be the temperature change. However, if the temperature change was negative that means that the temperature cooled down. I don't think an exothermic reaction would have the solution cool down.

 

[p21bass]

What's the definition of exothermic?

(Hint: How does exo- differ from endo-thermic?)Also, since you're doing this in a lab - aren't you measuring the temperature of the solution?