Calibrating a Calorimeter Equation

[Wesley Zhou 1F]

Hello,

I just wanted to clarify the equation used to calculate the calibration of a calorimeter.

In Monday 1/24's lecture, Dr. Lavelle gave the equation q = c∆T to use when calibrating a calorimeter. However, in the textbook, the equation is q = -c∆T.

How do we know whether to use a negative sign or not when using this equation?

Thanks

[Jessy Ji 2J]

I am not totally sure, but it might have to do with whether the reaction is endothermic or exothermic.

[Briana Chavez 3F]

Hi! Like the above post mentioned, the sign of the equation is determined by enthalpy. If the process is exothermic, then q is negative. If the process is endothermic, then q is positive. I believe that the same logic is applied to the other variables as well, just written differently.

[Stephen_Kim_1D]

I haven't checked the textbook, but I'm fairly sure it's because Professor Lavelle and the textbook are talking about different systems within the calorimeter. Lavelle is talking about q, the heat absorbed by the water surrounding the reaction so q is positive, but the textbook is talking about q, the heat released by the reaction causing the change in water temperature, so q is negative. Either way, the process is the same: the reaction is exothermic and releases heat, increasing the temperature of the water in the calorimeter.