Heat of Formation: Is Q Always Positive?

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In the discussion on heat of formation, the equation Q=ms∆T raises the question of whether heat is always positive. The heat of formation for magnesium reacting with hydrochloric acid is noted as -461.96 kJ/mol, while experimental results yielded 386.1 kJ/mol. The participant highlights that a negative temperature change would indicate cooling, which contradicts the expected behavior of an exothermic reaction. Clarification is sought on the definitions of exothermic and endothermic reactions. The importance of accurately measuring the temperature of the solution during the lab experiment is emphasized.
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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.
 
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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?
 

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