What would be the greatest difference in using an open ceramic coffee mug rather than an insulated mug with a lid as a calorimeter?

An insulated mug with a lid limits heat transfer between the liquid and the surroundings. An open ceramic mug is less insulated and uncovered, so more energy can enter or leave the liquid, making measurements less accurate. The greatest difference is increased exchange of energy with the surroundings; evaporation can also occur, but it is not the main calorimetry limitation described here.

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