How can an unknown Hreaction be determined using Hess's law?A.The free energy of the reaction is used to determine the H for the reaction.B.The unknown Hreaction is determined after the reaction is run in a calorimeter.C.The reaction is repeated at different temperatures to determine the Hreaction.D.Enthalpies from reaction steps are added to determine an unknown Hreaction.
Question
How can an unknown Hreaction be determined using Hess's law?A.The free energy of the reaction is used to determine the H for the reaction.B.The unknown Hreaction is determined after the reaction is run in a calorimeter.C.The reaction is repeated at different temperatures to determine the Hreaction.D.Enthalpies from reaction steps are added to determine an unknown Hreaction.
Solution
The correct answer is D. Enthalpies from reaction steps are added to determine an unknown Hreaction.
Here's the step-by-step process:
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Identify the target reaction for which you want to determine the enthalpy change (ΔH).
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Break down the target reaction into a series of steps for which the enthalpies are known. These steps are usually formation reactions or combustion reactions.
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Apply Hess's Law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for each step, regardless of the path taken.
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Add up the enthalpies for each step. If a reaction step is reversed, change the sign of ΔH for that step. If a reaction step is multiplied by a coefficient, multiply the ΔH for that step by the same coefficient.
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The sum of the enthalpies for each step gives the ΔH for the target reaction.
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