Education Technology

Designing Hot and Cold Packs

Published on 03/20/2006

Activity Overview

Purpose: To calculate the molar enthalpy of dissolving for three ionic solids, and to use this information to design a cold pack.
In this experiment you will measure the heat changes which occur from various salts dissolving in water, and then you will use this information to design a hot pack and a cold pack to generate a certain temperature change.

Before the Activity

Setup temperature probe and graphing calculator with EasyData. Set up equipment- cup, and three ionic salts.

During the Activity

  • Measure out 100 ml of distilled water in a graduated cylinder.
  • Add the water to the coffee cup. Lower the temperature probe into the water in the Styrofoam cup.
  • Measure out 5.0 g of NH4NO3. Record the exact mass of the salt used. Do no add it to the cup.
  • Begin recording the temperature of the water in the cup, Ti. Select to begin to monitor temperature. The temperature reading, in C, is displayed on the upper-right corner of the graph. Record the temperature for 5 seconds.
  • Add the 5.0 g of NH4NO3 to the water in the coffee cup and place the lid on top. Stir the solid until it dissolves.
  • Record the highest temperature reached,Tf.
  • Empty out the coffee cup, rinse. Now repeat steps #1- #10 using 5 grams CaCl2.
  • Calculations: 1. Calculate the molar heat ( H) for the dissolving of the three solids. The formula is given below nH substance=m * c * t
    2. m = mass of the substance in grams c= specific heat capacity of water (4.18 J/g*oC) t = temperature change in water in calorimeter

    After the Activity

    Problem: Based on your calculations in your experiment chose one of the salts and design a cold pack. The total mass of the pack (salt and water ) is 400 g. The temperature change desired is 10 ?C. Assume that the specific heat of the pack (salt and water) is 4.18 J/g?C and that the cold pack is initially at 23 ?C. Repeat the same procedure to design a hot pack.