You're correct that a positive ΔT in an exothermic reaction occurring in a calorimeter indicates that the temperature of the system is increasing. However, it's important to understand the sign convention used in thermodynamics.
In thermodynamics, the convention is to consider heat flow into the system as positive and heat flow out of the system as negative. This convention helps maintain consistency in the equations and calculations.
So, in the case of an exothermic reaction in a calorimeter, heat is being released by the system (the reaction) into the surroundings (calorimeter). This heat flow is considered negative because it's leaving the system. As a result, the heat transfer (q) for an exothermic reaction in a calorimeter is negative.
The positive ΔT you observe is a result of the calorimeter absorbing the released heat, causing the temperature of the calorimeter (and the surrounding water, if present) to increase. The positive ΔT reflects the change in temperature of the surroundings.
To summarize:
- Positive ΔT: Temperature of the surroundings (calorimeter and water, if present) increases.
- Negative q: Heat is released by the system (exothermic reaction) and transferred to the surroundings (calorimeter and water, if present).
It's crucial to keep track of the sign convention and consider the perspective of the system and the surroundings when analyzing thermodynamic processes.