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Unit 7: The Energy in Chemical Reactions—Thermodynamics and Enthalpy

Section 11: Conclusion

As we have seen, if a chemist has a thermometer and can carefully perform a controlled chemical reaction, the result is a direct measure of the heat that this reaction involved. If this reaction was carried out under constant pressure, of which our planet is a good example, then this heat is really a change in enthalpy. In the end, chemists are looking for the change in enthalpy for a reaction.

This is the core of all thermochemistry. Chemists can either run new experiments or work with Hess's Law and tables of enthalpies or bond enthalpies compiled over the centuries to find that needed value. From the enthalpy change for a reaction, we can figure out which foods and fuels are best to eat or use in our cars, or how cool a cold pack from the local drug store can get.

However, thermochemistry is only one part of a larger field of thermodynamics. The early work in thermodynamics—understanding the way a system transfers energy to and from its surroundings—allowed scientists to maximize the efficiency of steam engines and paved the way for the Industrial Revolution. Understanding the way chemical reactions release and absorb energy continues to be critical to our understanding of modern engines. The field of thermodynamics is of vital importance to many aspects of science, from the chemical reactions that power our bodies to the nuclear reactions that power the stars. As we will see in Unit 9, further developments in thermodynamics explained the driving forces behind every physical process since the Big Bang. This will lead us to understand why some chemical reactions take place while others do not.


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