Hess' Law Example
Enthalpy is a state function. This means that enthalpy is path independent: it does not matter how you determine enthalpy experimentally or through calculation, you always get the same answer. This means you can use whatever information you have about a reaction to solve for enthalpy change. This is called Hess' Law.
One way to apply Hess' Law is to break a complex reaction up into the sum of smaller reactions. If you know the enthalpies of the smaller reactions, you can simply sum them to determine the enthalpy of the larger reaction.
Watch this video to see how to apply Hess' law. Pay close attention to what happens when a small reaction is flipped or multiplied by a factor. Changing a reaction in any way changes the enthalpy of that reaction.
Source: Khan Academy, https://youtu.be/8bCL8TQZFKo
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