For context, if you are unsure what this question is in reference to, feel free to take a look at this video by Bozeman science and go forward to about the 2:00 mark. In a typical cellular respiration lab, in particular the one outlined by the College Board, a respirometer and some peas are used to measure the rate of respiration. What confuses me is why KOH (potassium hydroxide) is necessary so that the interior volume of the respirometer won't change. Why wouldn't the solid formed by 2KOH combining with CO2 (K2CO3) cause a change in volume, since it occupies space in the respirometer just like the gasses? Sorry if this seems like a silly question, I have very poor background knowledge of chemistry.
For an animation, feel free to view this link from Pearson.