Hand Warmer Design
Challenge
Background
 Chemical hand warmers are an effective, and environmentally safe way of
producing heat.
 They are made by using the heat of solvation of soluble ionic compounds.
 The ideal hand warmer:

Should increase in temperature by 20oC as quickly as possible
 Has a volume of about 50 mL
 Costs as little as possible to make
 Uses chemicals that are as environmentally friendly as possible.
 Your objective is to determine which substance would be the best for making
hand warmers.
Substance
Cost per 500 g ($)
NaCl
3.95
CaCl2
6.55
Na2CO3
6.15
LiCl
32.75
NH4Cl
9.05
Materials
 You will need many of the same materials we used in
Advanced Lab Skills when learning about Calorimetry.
 You might need more.
 Make sure you include any materials you use in your
lab report.
 Your will receive only 10.0 g of each substance.
Safety
 Safety is a big part of this lab.
 Part of your decision about what substance to use should be
the safety considerations of the substances.
 A substance that produces a lot of heat, but poses
significant health risks, might not be a good selection.
 You will use Flinn Scientific’s MSDS data base to collect
safety data for the five substances we will be using.
 http://www.flinnsci.com/msds-search.aspx
Procedure/Data
 It will be up to you to come up with a procedure and data table for this lab.
 Use your notes from our Advance Lab Skills calorimetry activity.
 When designing your procedure and data table keep in mind that we are
trying to determine.
 The first thing you are going to do is determine the calorimeter constant.
 Make sure you keep track of how much of each substance you use in each
trial of your experiment. You need to record the EXACT mass of the sample
you dissolve.
 Remember you will only get 10 g of each substance so use it wisely, don’t use
it all at once, you might want to do more than one trial.
Analysis Questions
1.
Show all of your work for your calculations of Ccal
2.
Create table that includes the following calculated quantities. (Show all
calculations as well). Do all calculations of all trials. You will report the
average ΔHsol for both trials.
3.
Which compounds, if any, can you eliminate as possible choices? Why?
4.
Of the possible compounds that could be used for your hand warmer,
calculate the amount in grams that would be needed to increase the
temperature of 50 mL of water by 20oC.
5.
Using the information provided in the background section calculate the cost
per hand warmer of each of the possible substances.
6.
Write a paragraph stating which compound you would use to create the ideal
hand warmer. Include all of the considerations such as, environmental safety,
cost, and ability to increase in temperature.
Equations
 ΔT = Tf – Ti
 qmix = mCΔT
 C = 4.184 J/goC
 qcal = Ccal x ΔT (This is the one I miss spoke about)
 qsol = - (qmix + qcal)
 ΔHsol = qsol/moles
 Also to answer question 4 you should DIVIDE 4.184 BY
ΔHsol to get moles.