Presentation: The Chemistry of Commercial Instant Hot and Cold Packs

Overview

• What is it?
• Brief History
• Uses
• How it works
• Environmental benefits and concerns
• Current research and future direction

What are Instant Hot and Cold Packs?

plastic bags containing different chemical compounds

When squeezed, hot packs create an exothermic reaction releasing heat

Cold packs create an endothermic reaction that absorbs heat and turns cold

These can be used for various types of injuries or pain

Speaker Notes: Instant hot and cold packs are plastic bags (similar to one used for an ice pack), which contain different chemical compounds. When these are squeezed, hot packs instantly create an exothermic reaction releasing heat, while cold packs instantly create an endothermic reaction which absorbs heat, becoming cold. These are generally used to treat various types of injury and pain.

Brief History of Heat Packs

In Japan around 1603-1868, many heated stones, wrapped them in cloth to provide a soothing heat application

These early “heating packs” required an external source of heat such as fire, therefore were not very practical

In 1911, the first electric heating pad (“El Warmo”) was designed by Earl Richardson

Problems arose such as fire hazard

This was due to old wires coming in contact with fabric

Lead to development of a heating pack requiring no external heat source or electricity

Speaker notes: In Japan from the early 1600’s all the way to the mid 1800’s, a popular method of heat therapy was heating stones using an open fire, and wrapping them in cloth to apply to the affected area. Although this was effective to some degree, it required fire as a heat source, which was not available at all times, making this method not very practical. It was not until 1911 when Earl Richardson designed the first electrical heating pad he called “El Warmo”. This form of heat therapy was more practical than the last, and was more accessible since it only required electricity. However, problems arose from this such as old wires coming in contact with fabric, creating a fire hazard. This lead to the development of an instant heat pack which required no external heat or energy source.

Brief History of Cold Packs

The use of cold for therapy evolved in 3 stages:

19th Century- Natural ice was used for cold therapy (e.g. snow to numb soldiers in 1812)

1890’s to 1950- Began experimenting with substitutes for natural ice

1950 to present- Chemical cold packs were developed

Speaker Notes: The use of cold therapy for swelling, injury and numbing has been dated back to the 19th century during the war. At this time, doctors used natural ice or snow to numb soldiers. From here, cold therapy evolved and people began using substitutes for natural ice. Ice was made at home using an ice cube tray and placing ice in cloth or a plastic bag. After this, gel ice packs were created that required freezing prior to use. And finally, chemical cold packs were developed which are instant, not requiring an external source of cooling.

Uses and Benefits of Hot Packs

Heat increases blood flow to restore movement to injured tissue

Reduce joint stiffness and pain

Relaxes tight muscles, causes tissue to relax

Decreases pain caused by muscle tension or spasms

Instantly hot

Portable and easy to use

Slide 9: Uses and Benefits of Cold Packs

Reduces blood flow to a particular area, reducing inflammation and swelling

Can temporarily reduce nerve activity which can relieve pain

Instant, ready to use

Good for emergency

Small, portable and safe

The Chemistry of Instant Hot and Cold Packs

Endothermic and exothermic reactions occur as a result of salt dissolving in water

Salt dissociates, causing hot packs t0 release heat, and cold packs to absorb heat

The way this occurs is dependent on the chemicals used

Speaker Notes: Most instant hot and cold packs function by dissolving some sort of salt in water. When this dissociation occurs (see figure 1 for example) the endothermic or exothermic reactions take place. The chemical compounds used differ between the brand and type of hot and cold packs.

Calcium Chloride:

Speaker Notes: The simplest hot packs use calcium chloride. When the instructions on the hot pack are followed (for example “squeeze here”), The water mixes with the Calcium Chloride, which then dissociates into its ions Ca2+ and Cl- (figure 2), initiating the release of heat as shown in the potential energy diagram for this exothermic reaction. The temperature of the hot pack can reach up to 90 degrees almost instantly.

Magnesium Sulfate

Speaker Notes: Magnesium sulfate also produces a large amount of heat when it is dissolved in water. The process that takes place inside a hot pack with magnesium sulfate is very similar to that of calcium chloride. Inside a hot pack with magnesium sulfate, there is a small pouch filled with water, and it is surrounded by magnesium sulfate in crystal form. When the small pouch is broken, the crystals begin to dissolve in the water (figure 3), causing an exothermic reaction as seen in the potential energy diagram.

Crystallizes at high temperature

High boiling and melting point

Speaker Notes:The process that occurs in a hot pack containing sodium acetate is slightly more complicated than the previous two, however it is more effective since they are reusable. Since sodium acetate freezes at 54 degrees, and will stay in solution at temperatures below its crystallization point. These heat packs contain a sodium acetate and water solution as well as a small metal disk that is isolated from the solution. To initiate crystallization, pressure can be applied to the small metal disk, which causes a few molecules to crystallize. As a result, the rest of the molecules jump to solidify afterwards, causing the temperature to raise to 54 degrees (ex figure 5). These types of heat packs can be reused by simply boiling the solution to bring it back to a liquid state, and repeating the process (figure 4).

Speaker Notes : Ammonium nitrate has traditionally been the most common chemical found in instant cold packs. Inside the cold pack, a small pouch of water is kept separate from the chemical. When the pouch is broken, the dissolving of NH4NO3 begins and splits into its ions as shown in figure 6. The solution absorbs the energy from its surroundings, causing the temperature to drop significantly as shown in the potential energy diagram. Although this chemical is quite effective for instant cold packs, it can have harmful effects on the body when swallowed, inhaled, or in contact with skin. For this reason, many companies choose to use non toxic urea in cold packs instead.

Speaker Notes: The solution absorbs the energy from its surroundings, causing the temperature to drop significantly as shown in the potential energy diagram. Although this chemical is quite effective for instant cold packs, it can have harmful effects on the body when swallowed, inhaled, or in contact with skin. For this reason, many companies choose to use non toxic urea in cold packs instead.

 Urea : CO(NH2)2

Aka carbamide

Organic compound

CO(NH2)2 (s) CO(NH2)2 (aq)

Does not dissociate into ions

Highly soluble

Polar molecule

Hydrogen bonding

Speaker Notes: Cold packs containing urea undergo a similar process to cold packs containing ammonium nitrate, without the harmful side effects. These cold packs again contain a small pouch of water surrounded by urea in its solid state. When the pouch is broken, urea is dissolved and the solution becomes cold. The only difference is that since urea is a molecular compound, it does not dissociate into ions

Environmental Implications

No burning needed to create heat

No incomplete combustion involved

No harmful byproducts as a result

No external source of heating or cooling needed

No unnecessary wasted energy

Some types are reusable

Speaker Notes: A few environmental benefits of using instant hot and cold packs are:

No burning is involved in the production of heat for instant heat packs. Burning any substance can be hazardous to the environment since it can produce harmful byproducts. This is avoided by using instant hot packs.

No external source of heating or cooling is needed for the instant hot and cold packs to function. For example, instant cold packs do not need to be cooled in the freezer prior to use. Refrigerators and freezers use energy that was usually created by burning fossil fuels, which causes damage to the ozone layer. Using instant cold packs do not require freezing, eliminating wasted electricity.

Some types of hot and cold packs are reusable, for example sodium acetate hot packs. Re using the hot packs can reduce the amount of plastic waste in landfills and oceans.

 Environmental Concerns of Instant Hot and Cold Packs

Packaging used is plastic

Polymers cannot decompose naturally

Need to be burned, causing harmful byproducts

Speaker Notes: The main environmental concern regarding instant hot and cold packs is the packaging used. The bags holding the chemicals are made of plastic. Since all plastics are polymers, they do not naturally decompose naturally, causing plastic to add to our landfills and pollute our oceans. Furthermore, The decomposition of polymers requires unnatural forms of decomposition such as burning, which leads to incomplete combustion, and byproducts like carbon monoxide that are harmful for the environment.

Not a lot of current research

In the future, make all hot and cold packs reusable

Eliminate plastic use in hot and cold packs

Speaker Notes: Since the chemistry behind instant hot and cold packs is quite simple, not a lot of research is being directed towards this topic. However, there are many things that can be improved on to make hot and cold packs more efficient in the future. For example, all types of hot and cold packs should be made reusable. The chemistry involved would have to be quite different, since currently, dissociation reactions occur inside most hot and cold packs. These types cannot be reused because the compounds have been mixed with water and separated into their ions, and this cannot be reversed using the simple components of today’s hot and cold packs. In the future, hot and cold packs should be made out of a different substance than plastic, so that they are not contributors to plastic pollution.

Instant cold packs contain chemicals that dissociate into ions when mixed with water, absorbing heat in an endothermic reaction

Instant cold packs contain chemicals that dissociate into ions when mixed with water, releasing heat in an exothermic reaction

Hot packs are used to increase blood flow and relax muscles

Cold packs are used to reduce blood flow and swelling

Instant hot and cold packs don’t require external energy sources, benefiting the environment

Many types are not reusable, and also contribute to plastic pollution.