1.9: Experiment 8 - Enthalpy of Reaction


Ancillary Documents

Learning Objectives

By the end of this lab, students should be able to:

• Calculate the specific heat capacity of an unknown metal.
• Design an experiment to determine the calorimeter constant.
• Predict factors that might influence your experimental results, and how to minimize error.
• Correlate variability in data to limitations in the physical set up of our lab.
• Extract information from graphical representations.
• Calculate heat of neutralization for a salt (theoretical and actual molar heat of reaction) using experimental data.

Prior knowledge:

Calorimetry is the science of measuring heat flow. Heat is defined as thermal energy flowing from an object at a higher temperature to one at a lower temperature. For example, if you drop a coin into a cup with hot water, the temperature of the coin will go up until it is at the same temperature as the boiling water. This will happen because the coin will be absorbing the heat from the water.

Calorimetry is based on the First Law of Thermodynamics that states that energy cannot be created nor destroyed. The heat of neutralization that is lost in the chemical reaction (the system) is gained by the calorimeter and its contents (the surroundings).

This is an IOT lab, where you will be asked to design the experiment and your TA will perform it while streaming data in real time to a Google Sheet. To make this possible your TA will be using Raspberry Pi and Vernier temperature probe.

Procedure

Make copies of your assignments for this lab by clicking on Google Docs links in Ancillary Documents section above.

Week One

Determination of Calorimetry Constant

In the ideal world, we would have a calorimeter that is so well insulated, that all of the heat gained or lost during the reaction is contained inside the calorimeter completely. You can read more about the heat transfer in an ideal calorimeter here. In reality some of it "escapes", since the calorimeter we have isn't a perfect insulator. Our calorimeter will absorb and lose heat. Keep that in mind when you design your experiment.

To make sure you get accurate results you need to calculate the calorimeter constant, which is the calorimeter's heat capacitance. We use capital $$C$$ to represent the heat capacitance of an object, so for the calorimeter constant we will use $$C_{cal}$$. Calorimeter constant has to be measured for every calorimeter and this is going to be the first part of this lab.

If we look at the equation $$q_{C} = - \;q_{H}$$ and apply it to our real calorimeter we will see, that there are two cold objects that contribute to $$q_{C}$$ - the cold substance and the calorimeter itself. This means that

$q_{C}\;= \left( \;m_{C}\;\times \;c_{C}\;\times \;\Delta T_{C}\; \right) + \left( \;C_{cal}\;\times \;\Delta T_{C} \right)$

Interactive Element

Specific Heat Capacity

Work with your group in Zoom Breakout Rooms to find specific heat capacity of an unknown metal. This is an individual assignment, but you can discuss it with your group members.

Week Two

Prelab Assignment

Interactive Element

Heat of Neutralization Individual Assignment

Interactive Element

Heat of Neutralization Lab Report

During this lab you will first access the Google Sheet (link is in your Lab Report), the TA will perform the experiment and stream data directly to the Google Sheet. The data points will be added to the graph automatically. You need to copy the Google Sheet with the data and the graph, add a trendline and find TH and TC from the graph. Take a screenshot of your graph (make sure it has all necessary elements) and include it in your Lab Report.

Interactive Element