Experiment 13: Enthalpy Changes for AP Chemistry
For a quick review on stoichiometry, refer to the following concepts:
- Moles, Molar Mass, and Molarity for AP Chemistry
- Percent Composition and Empirical Formulas for AP Chemistry
- Reaction Stoichiometry for AP Chemistry
- Limiting Reactants for AP Chemistry
- Percent Yield for AP Chemistry
In this experiment the heat change associated with a process is calculated. Various substances are added to a calorimeter (usually a polystyrene cup), and the initial and the final temperatures are measured. (See the Stoichiometry chapter.)
- analytical balance
- graduated cylinder
- The masses of various substances are determined
- The volume of a solution or solvent is determined with a graduated cylinder.
- Measure the initial temperature.
- Measure the final temperature.
The masses are converted to moles using the molar mass. The volumes of solutions may be converted to moles using the molarity.
The mass of a solvent or solution may be calculated from the volume and density.
A total mass may need to be calculated by adding the individual masses together.
The change in temperature (ΔT) is calculated from the difference between the final and initial temperatures.
The energy (joules or calories) is calculated by multiplying the mass times the change in temperature times the specific heat (from a table).
The enthalpy change is calculated by dividing the calculated energy by the moles, mass, or some other designated quantity.
Any reaction or phase change may be used.
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