Description
How to make your own hand warmers that heat up to around 50°C when activated, and can be used in the mountains, e.g. to keep warm when hiking.
Summary
Contents
- 1 Description
- 2 Summary
- 3 Introduction
- 4 Step 1 - Calculating quantities
- 5 Step 2 - Cleaning the equipment
- 6 Step 3 - Mixing the reagents
- 7 Step 4 - Heating + evaporation
- 8 Step 5 - Filling
- 9 Step 6 - Refilling the hand warmers
- 10 Step 7 - Use of hand warmers
- 11 Step 8 - Notes on these hand warmers:
- 12 Step 9 - Unresolved problem
- 13 Step 10 - Pouches
- 14 Notes and references
- 15 Comments
Introduction
In the mountains, you're often exposed to the cold, particularly the extremities of the body (hands + feet).
Some people really struggle to keep warm, and ski touring (which avoids using expensive and polluting ski lifts!) can become a nightmare.
Some sports shops offer hand-warmers for a little extra comfort. These are small plastic packets that warm up to around 50°C when activated.
Some are reusable and cost around 20€ a pair; others are not reusable, costing around 15€ for 30.
In a complete low-tech approach, we should first and foremost question this need for comfort. For those who may already have given this in-depth thought but still want to have hand warmers, it's possible to make ones yourself, (almost totally) reusable (see discussion about problems to be solved) and very economical!
Materials
- Sodium bicarbonate (baking soda)
- Vinegar
- Container for warmers (here we use empty compote sachets)
The tutorial will go over the quantities - as they depend on the concentration of the vinegar.
NB: only use compote sachets which close properly!
Tools
- Saucepan
- Scales
- Spoon
- Funnel
- Glass
- Measuring glass
Step 1 - Calculating quantities
Quantities for one warmer...the amount of vinegar depends on its concentration.
Quantité pour une chaufferette
Quantity for one warmer
35g baking soda
| Concentration of vinegar [%] | Mass of vinegar [g] | Approximate volume of vinegar [mL] |
| 6 | 415 | 415 |
| 8 | 315 | 315 |
| 10 | 250 | 250 |
| 12 | 210 | 210 |
| 14 | 180 | 180 |
| 16 | 155 | 155 |
These values are approximate. You can find out how to calculate them in the theoretical section.
NB: The density of vinegar is very close to that of water, 1kg for 1L.
Step 2 - Cleaning the equipment
Making these hand warmers involves chemistry, and chemistry doesn't like impurities. We strongly advise you to clean all utensils properly with soap and water, especially the containers used for the warmers (if you use the same ones as us here, there's a risk of compote remaining inside them!).
Step 3 - Mixing the reagents
Safety
- Vinegar irritates the skin and eyes. Wear safety goggles when mixing and watch out for splashes.
Step 1: mix the vinegar and bicarbonate of soda. Start by pouring the right amount of vinegar into the pan. Then add the bicarb of soda slowly. Stir until there is no more foam - this is how you know the chemical reaction is complete.
NB
- Pour in the bicarbonate of soda slowly, as the reaction produces CO2 gas, causing the solution to foam.
- This stage takes time, but it's best to do it properly so that all the vinegar reacts. If there is any vinegar left over, you'll smell its nauseating odour during the next stage!
- The more warmers you make, the longer the reaction will take. For 5 warmers, expect about 20 minutes of mixing!
Step 4 - Heating + evaporation
Safety
- The substance obtained from the reaction of vinegar + sodium bicarbonate is sodium ethanoate. This substance can irritate the eyes; we advise wearing safety goggles.
- Slight risk of burns, possible splashes if using large quantities on a high-powered hob.
When stage 1 is complete, put the saucepan on a high heat to evaporate most of the excess water. NB: leave a little water to obtain the right consistency. When a thin film begins to appear on the surface, the substance is ready; turn the heat off.
NB
- There's a lot of water to evaporate, so this stage takes a while (again, the more warmers you make, the longer it takes).
- During this stage, nothing happens for a long time, but in the end everything happens very quickly. Be vigilant as soon as the liquid becomes slightly cloudy + yellow.
- Generally, crystals will appear on the edges of the pan towards the end.
- If you accidentally leave the liquid on the heat for too long, it will solidify completely. In this case, turn off the heat and add water quickly (not too much, just enough to see all the solid become liquid again). You can then put it back on the heat, stirring to help the last crystals liquify. Don't worry, the hand warmers will still work!
- Towards the end of the reaction, it should smell like a baked cake. Although it smells nice, avoid inhaling too much of it!
Step 5 - Filling
Safety
- Risk of burns - the liquid going into the warmer containers is very hot (around 100°C at first).
- If the liquid comes into contact with the skin at less than 60°C, it will solidify and heat up. The solid sticks to the skin, but don't panic, add a little water and it will go away on its own. Try and rinse off quickly with water to avoid burning yourself.
The aim of this step is to fill the containers with the substance obtained in step 4.
Two people are needed for this stage, as it is difficult to hold the containers and pour at the same time.
The person holding the container can wear gloves to avoid burns.
Insert funnel into the containers and pour contents in gently.
NB
- Leave a small gap for air to pass when pouring. Be careful not to completely block the hole with the funnel, as this could cause the liquid to overflow and burn :(
- Between filling each warmer, stir the pan to mix the liquid and prevent the surface from solidifying.
- The liquid solidifies at around 58°C, so pour it in before it reaches this temperature, otherwise the funnel will block up. Don't pour too quickly or you could get burnt. If the substance starts to cool too quickly, simply add a little water and repeat step 4.
- If the funnel is completely blocked, you can pour in some hot water and the solid will quickly liquidify and flow!
- NB: fill the container 3/4 full to avoid auto-activation!
Step 6 - Refilling the hand warmers
The hand warmers are now ready to be charged up!
To heat a warmer, place in boiling water for 10-15 minutes. Then leave it to cool until it reaches room temperature.
They're now charged up and ready for use in the mountains or elsewhere!
Step 7 - Use of hand warmers
Once you're out in the mountains in the cold, activate them following these instructions:
Voici les étapes :
- Froid
2. Ouvrir en dévissant
3. Boucher avec un doigt
4. Retourner et secouer
5. Fermer
6. Chaud
They heat up to around 50°C. To maintain the heat, we advise insulating them by putting them in your gloves / pockets.
Safety
Warning: Do not suddenly/rapidly re-heat frostbitten limbs. The use of these hand warmers is preventive, to prevent cold, not to heat an body part in critical condition.
Do not alternate between hot and cold when suffering from frostbite. Put on dry clothes and have a luke-warm bath (e.g. 37°C), once you're in a safe place.
Step 8 - Notes on these hand warmers:
It's been very interesting for me to experiment and gradually improve this process following personal observations!
Fabrication de l'éthanoate de sodium, réaction chimique
Sodium ethanoate = a product of the reaction between ethanoic acid and sodium bicarbonate.
Cette réaction produit aussi de l'eau est du CO2.
Calcule des quantités
This part isn't much fun, so skip it if you're not a big fan of chemistry calculations! But it is necessary if you want to recalculate everything yourself.
To determine the quantities of ethanoic acid and sodium bicarbonate to mix, we assume that the reaction is absolute. In order to optimise the process, mix the reagents in what are known as 'stoichiometric quantities'. When you add exactly these quantities, all the reagents are consumed; all that's left at the end of the reaction is the product!
Here, 1 molecule of ethanoic acid reacts with 1 molecule of sodium bicarbonate. The same number of "quantities of matter" (moles) of each of the two reagents must therefore be added in order to reach the stoichiometric quantities.
Taking this into account, calculate the quantity of material corresponding to 35g of bicarbonate (for 1 hand warmer).
Next, calculate the mass of acetic acid needed to obtain exactly the same quantity of substance (which will depend on its molar mass).
Finally, if 8% vinegar has 0.08g of ethanoic acid per 100mL, in this way we calculate the volume of vinegar to obtain exactly the right mass of ethanoic acid.
OR you can calculate the mass of vinegar rather than the volume (useful if you don't have a measuring glass). Fortunately, vinegar has pretty much the same density as water, so 1kg of vinegar for 1l of vinegar.
There are a few educational resources on basic calculations in solution chemistry on the internet if you're interested. It's a subject that is covered at the beginning of secondary school in France.
Comprendre par ses propres sens
This reaction is fun to experiment with because it's very visual: the production of CO2 produces foam - in this way we can then see whether all the molecules have reacted properly.
Pourquoi la réaction (mélange) est si longue ?
The reaction takes a fair amount of time, don't forget to stir/mix! But what happens in terms of molecules that takes so much time?
After a few seconds of reaction, in the saucepan, there's lots of water, the reactants + a few products that have already been created. In order to react, two molecules of reageant must collide.
But how can we make them collide efficiently in amongst all this mess?
In technical terms, reaction kinetics refers to the speed at which the reaction takes place and the limiting phenomenon refers to the phenomenon that imposes this speed.
The collision of the molecules is the slowest part, i.e. the mass transfer.
.
Vous avez dit cristallisation ?
What about crystallisation?
We mentioned the problem of crystallisation if the liquid is heated for too long. This might seem counter-intuitive. Normally, by increasing the temperature, you go from solid to liquid, not the other way round.
Crystallisation happens sodium ethanoate trihydrate dehydrates to form anhydrous sodium ethanoate. The trihydrate substance, what we want for our warmers, liquefies if we heat it above 58°C. On the other hand, the anhydrous substance only liquefies at 324°C. So when you remove the water from a molecule, Bang! It becomes anhydrous and solidifies instantly, because we're well below 324°C!
At the beginning, there's an excess of water, so it's this water that evaporates. But as soon as there is almost no water left, we start to '"dehydrate'" the molecule, "'hence the appearance of crystals at the end'", then, gradually'"a solid film'".
Comprendre pour mieux agir !
Understanding the phenomenon allows you to judge when to stop step 4: when the first crystals appear, you know that the remaining liquid is not water but sodium ethanoate trihydrate. If there was still water present, it would evaporate and no crystals would appear!
.
Le plus important : Pourquoi les chaufferettes chauffent ?
Hand warmers work thanks to the process of supercooling! To find out more:
Step 9 - Unresolved problem
Des chaufferettes presque réutilisables !
In theory, the hand warmers should be reusable. In reality, each time they are used it becomes more difficult to reactivate them. I haven't been able to solve this mystery yet, but maybe you can!
They can be reused a number of times if you're prepared to wait a while and go over them several times to reactivate them.
For the more persistent among us, inserting a metal rod and mixing it will activate it more effectively - you'll be able to reuse it for longer using this method. To do this, you can use the tip of a small screwdriver, a screw or any other metal object, mix it for a while and remove it once it starts to heat back up :)
Quelques auto-activations imprévues
The warmers may activate by themselves. Sometimes this happens when recharging, after warming them up. This can be annoying because you then have to charge them up again.
To check the hand warmer is ready to use, simply check that it is in liquid state. If it is, you're ready to go.
Step 10 - Pouches
Fabric pouches enhance the aesthetic of the hand warmers. To hide and hold the plastic compotes: a 20 x 20 cm piece of fabric, hemmed at the top, which is where the compote will slide in. Laying out the plastic instruction labels and sewing them at the top and bottom is enough, before sewing the pouch itself on the side and bottom.
Notes and references
Noé Beaupere. PILOTAGE DE LA LIBÉRATION DE CHALEUR ET ÉTUDE DU VIEILLISSEMENT DE MATÉRIAUX À CHANGEMENT DE PHASE. Sciences de l’ingénieur [physics]. Université d’Artois, 2019. Français. https://theses.hal.science/tel-03160528
Published
Français
English
Deutsch
Español
Italiano
Português