Calorimetry Lab Constructing a Commercial Hot Pack or Cold Pack

Calorimetry Lab: Constructing a Commercial Hot Pack or Cold Pack Background Have you ever injured yourself and been given an instant cold pack or hot pack? Many of these function though the mixing of a salt and water. To use the pack it is squeezed which breaks an inner packet, releasing water which then mixes with the salt contained. Depending on the salt contained the temperature of the pack may increase or decrease. How can you determine how much heat each absorbs or releases? Calorimetry is the science of measuring heat. Many chemical and physical transformations involve energy transfer in the form of heat. The magnitude and direction of heat may be determined using a calorimeter. In reactions that occur in aqueous solutions the energy is transferred to or taken away from the water. The calorimeter is an apparatus that is insulated and prevents heat from flowing in or out. Since the experiment is run under constant pressure (atmospheric), the change in temperature of the water is due to the enthalpy of reaction, in which the heat of reaction may be calculated using the values measured for change in temperature of the water. The heat transfer (change in enthalpy) in a reaction is related to the mass of the solution (m), the specific heat capacity of the solution, and the temperature change (ΔT = Tfinal – Tinitial) in the equation q=mCΔT, where the specific heat capacity of a substance is the amount of energy required to raise 1 gram of the substance 1 degree Celsius. The specific heat capacity of water is fairly high at is 4.186J/(°C x g). In experiments conducted in solution, the specific heat capacity of water is generally used. The enthalpy change in the reaction, ΔHrxn, is a measure of the heat flow and at constant pressure is equal to heat flow, qrxn. Enthalpy change, however is generally written as a molar quantity. To calculate the molar enthalpy of a reaction, divide the amount of heat in the reaction by the number of moles of reactant or product ΔHrxn = If a process increases the solution temperature it is exothermic (negative ΔH), whereas if a process increases the solution temperature it is endothermic (positive ΔH). EXPERIMENTAL PARAMETERS • In this lab you will be constructing a chemical hot pack or cold pack. • As some commercial chemical cold packs are designed to reach a temperature of 3°C and some commercial hot packs are designed to reach a temperature of 50°C, these values are what you should try attain in your hot pack or cold pack. STRUCTURE OF THE LAB • PART ONE: Run some calorimetry experiments of your own design with standard labware in an effort to determine necessary quantities of both salt and water to use in your pack. It is highly suggested that you determine the ΔH of solution for this process. • PART TWO: Run some design tests using either empty containers or only water to design a closed system pack that will remain closed until activated. The activation process cannot open the pack and MUST be done from the outside. The pack cannot be activated accidentally, and should be sturdy enough to be dropped on the floor without being activated. • PART THREE: Combine your quantities of water and salt from part one with your pack design in part two. When you have done this, call Mrs. Julian over. She will watch you activate your pack. You must consider how you will monitor the temperature of the pack. You only get one shot at this, and Mrs. Julian MUST watch you do it to verify the temperature. • If you are successful in attaining the goal temperatures (plus or minus 2 degrees Celsius) in your FIRST AND ONLY attempt with your hot pack or cold pack, you will win bonus points on the end-of-quarter cumulative exam. • YOU ARE LIMITED TO A TOTAL OF 60 GRAMS OF YOUR SALT FOR THE ENTIRE LAB. As you only have 60g of the chemical, you will need to carefully plan before you begin your investigation. It is highly suggested that you run some initial experiments to determine the enthalpy of solution before constructing your hot pack or cold pack. • You have one class period to complete this lab challenge.