And when we talk about gases, we need to remember that gases compress and expand. So what Bond kilometers do is they intentionally keep the volume constant by letting the reaction occur in a steel container, in a steel cylinder. So no expansion in the steel cylinder occurs. So let's compare box perimeters to coffee cup calorimeters. In a coffee cup, caliber, expansion or compression was not a problem. And that's because our reactants were liquids and solids.