Question

In calorimetry, we often define `q_(sys) = 0`. What assumptions about the calorimeter make this possible?

Answer 1

If you mean with respect to the surroundings, then it must mean that heat cannot flow in from the surroundings,

The walls of the container must therefore be impermeable and insulated. In such a calorimeter, `q` flowing into the system is `0`, and we say that the system is closed with respect to the surroundings.

Overall, the calorimeter would have to be closed, with impermeable, insulated walls.