# AP Chemistry – Lab 07 – Hess’s Law

Purpose

The goal of this lab is to verify Hess’s Law: if the sum of two chemical reactions is a third reaction then the sum of the two reaction enthalpies is the enthalpy of the third.

Procedure Notes [LINK]

- make sure that the calorimeter is clean and dry before each use
- do not contaminate the solutions with each other as that will distory the results
- any acid spill – neutralize with baking soda
- any base spill – neutralize with vinegar
- the smell of ammonia is powerful – be very careful and do not directly smell
- be sure and ask how to be coached on using the GLX to save files

Data Processing

- be sure and determine the heat capacity of the calorimeter
- determine the change in enthalpy for each reaction (per mole)
- determine the change in enthalpy for the unknown reaction (per mole) using your data
- calculate the percent difference between the theoretical and experimental values
- be sure and complete pre-lab if you did not already do so

Posting Information

- make sure the data, calculations, graphs are in the LNB
- the final data, calcs, graphs, results should be posted to Tumblr in polished, final form

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