Hess's Law states that the total enthalpy change for a chemical reaction is the same, regardless of the pathway taken, provided the initial and final states are the same. This principle allows for the calculation of the enthalpy change of a desired reaction by using the enthalpy changes of multiple intermediate reactions that add up to the overall reaction. By summing these known enthalpy changes, one can derive the enthalpy of the target reaction, even if it cannot be measured directly. This makes Hess's Law a valuable tool in thermochemistry for determining reaction enthalpies.
Hess's and Wegener's theories are interconnected in their exploration of continental movement and plate tectonics. Alfred Wegener proposed the theory of continental drift, suggesting that continents were once joined and have since moved apart. Harry Hess later contributed to this understanding with his theory of seafloor spreading, which explained how new oceanic crust forms at mid-ocean ridges and pushes continents apart. Together, their ideas laid the foundation for the modern understanding of plate tectonics.
One key piece of evidence not included in support of Harry Hess's hypothesis of sea-floor spreading was the discovery of paleomagnetic data. While Hess's theory focused on the creation of new oceanic crust at mid-ocean ridges and the recycling of crust at subduction zones, the paleomagnetic records provided insights into the historical movement of continents and the magnetic orientation of rocks, which later supported the theory of plate tectonics. Other evidence, such as the age of oceanic crust and the distribution of fossils, played a more direct role in supporting his hypothesis.