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Why is it difficult to measure enthalpy change of rxn directly?

In a past exam question about the thermal decomposition of calcium carbonate, u have to calculate the enthalpy change of reaction. Part of the question asks why it would be difficult to measure enthalpy change of rxn directly by expt?

CaCO3(s) -> CaO(s) + CO2(g)

It's only 1 mark

Reply 1

beertrix

Id put "loss of heat to surroundings" - never gonna get a perfect/accurate reading.

I'm not 100% though.

Reply 2

charco

Study Forum Helper

This is an endothermic reaction. To cause it to happen you have to apply lots of heat. Most of this heat will be lost to the surroundings - it simply isn't possible to know how much gets absorbed during the reaction.

Reply 3

RickHendricks

Original post by charco

what if it's exothermic reaction?

Reply 4

charco

Study Forum Helper

Original post by RickHendricks

what if it's exothermic reaction?

But the reaction the OP is discussing is endothermic!

However, the same principles apply. If you can "capture" the energy released in an exothermic reaction then you can calculate the enthalpy change.

In many cases this is simply not possible. In aqueous solution reactions, or combustion reactions it becomes feasible and this is the basis behind calorimetry.