Can a Calorimeter Measure Fast Chemical Reactions?

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The discussion centers on the limitations of calorimetry in measuring the heat of fast chemical reactions. A calorimeter is unable to accurately capture the rapid changes in temperature associated with quick reactions, leading to challenges in determining the heat of a single step in a multistep process. The water in the calorimeter does indeed heat up or cool down over time, which complicates the measurement. For fast single-step reactions, it is often necessary to use Hess's Law to calculate enthalpy variations, as direct calorimetric measurements may not provide reliable data. The conversation emphasizes the need for alternative methods to assess reaction enthalpies when dealing with quick reactions.
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Question about enthalpy and fast reactions.
My book introduces Thermochemistry with the concept of heat and how a calorimeter works. After that, it explains the story behind Hess Law and says that one of the reasons it was created is because a calorimeter can't calculate fast chemical reactions, but it doesn't really say the problem with it. Why can't it calculate fast chemical reactions? Won't the water in the calorimeter heat up or cool down after some time?
 
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How are you going to determine a heat of a single step of a quick multistep reaction?
 
Supposing a fast single step reaction, is it possible to calculate its enthalpy variation using a calorimeter or I would need Hess Law to calculate it using other reactions?
 
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