Self cooling water bottle

My hypothesis is that the urea when dissolved in water, will be endothermic, cooling the water contained. This is because urea needs to take in energy to dissolve, which means it will absorb the heat in the water, while dissolving. I also predict that the water will cool to 2 degrees celsius from 20 degrees celsius with 27ml of water / 47g of urea (NH2)(2CO)

Definitions

Endothermic: An endothermic reaction is a type of endergonic reaction. However, not all endergonic reactions are endothermic. Endothermic reactions involve heat absorption. Other forms of energy that might be absorbed in an endergonic reaction include sound and light.

Urea is used for many things including some cold packs, fertilizer and feed supplement, and also is used for plastics and drugs.

Regenerating

I found that urea will melt at 135 degrees celsius. Urea will evaporate at 155 degrees. However, instead of turning directly into a gas, it splits into many things, including ammonium cyanate. This is an irritant and can cause brathing problems, and can also be absorebd through skin. It can cause confusion, dizziness, convulsions, anxiety and even unconsciousness or death. This can be avoided by only heating the mixture to about ~50 degrees celsius. This will take longer to evaporate all water, but will prevent urea from dissolving and should keep most of the urea intact.

My variables are as following:

Controlled: Cooling mechanisim, Temperature of water at starting, and temp of room.

Manipulated: Amount of urea, Amount of water

My procedure for experiment 1 cooling is as following

1. Measure out 125ml of water

2. Measure out 100g of urea

3. Measure out

I observed that the urea cooled the water quite quickly. In our first trial, it went from 25 degrees to 6 degrees in a matter of seconds. This is not the performance we expected, with the Q = MΔT, wich gave us a delta of -11.062, but instead, we got a delta of about 20 degrees. We calculated a final temp of 13 degrees and got to 6 degrees. I wonder why our calculations were so off. Perhaps, our research variables on urea and water were wrong?

I observed that after scraping off urea that I had more urea then when I started. I think this is because of water in the urea, even after drying for a night. When first extracted, we had 113.5g avg. urea, and after a night of drying, it had 111g of urea. I hope after a day of drying, it will be fully dry and we will be close to 100g.

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Specific heat of water | J/g°C | 4.18 | 4.18 | 4.18 | 4.18 | 4.18 | 4.18 | 4.18 | 4.18

Dissolution Enthalpy of urea | J/G | -57.8 | -57.8 | -57.8 | -57.8 | -57.8 | -57.8 | -57.8 | -57.8

Volume of water | ml | 500 | 250 | 125 | 500 | 125 | 1.953125 | 29 | 29

Mass of urea | g | 250 | 250 | 100 | 500 | 200 | 3.125 | 47 | 47

Starting temp | °C | 25 | 25 | 25 | 25 | 25 | 25 | 25 | 25

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Total energy absorbed | | -14450 | -14450 | -5780 | -28900 | -11560 | -180.625 | -2716.6 | -2716.6

Delta T | | -6.91387559808612 | -13.8277511961722 | -11.0622009569378 | -13.8277511961722 | -22.1244019138756 | -22.1244019138756 | -22.4104933179343 | -22.4104933179343

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Final temp | | 18.0861244019139 | 11.1722488038278 | 13.9377990430622 | 11.1722488038278 | 2.8755980861244 | 2.8755980861244 | 2.5895066820657 | 2.5895066820657

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Tau | | 7.5 | 12.5 | 21 | 10 | 22 | 1280.03125 | 86.6768965517241 | 86.6768965517241

I conclude that after my experiment, using urea to cool water is possible, and is efficent. I see that recovery is also possible, and that this design could be formed into a product by an entrepreneur and is something people might buy. I think that this is better than one-time use cold packs, because these aren't as good for the enviroment. After 1 day of drying the urea, we got 111g. After two days, we got 108g, and after 4 days we got 102g meaning the urea had most likely fully dried. I conclude that all of the urea was recovered and is probably 2g over due to minerals in water.

This water bottle can be used to cool water in the real world. People could bring this on maybe a hiking trip. You can bring lots of urea with you and be able to cool your bottle of water very quickly and with no electricity. You can operate the cooling process mobile so while on the move, you could continue to be able to cool your water.

I have a few sources of error. I had the container open, casuing the water to cool faster due to ambient. Second, I used unfiltered water, possibly containing minerals. This caused the urea to possible weigh too much.

Endothermic defenition: Helmenstine, Anne Marie, Ph.D. "Examples of Endothermic Reactions." ThoughtCo, Jun. 7, 2024, thoughtco.com/endothermic-reaction-examples-608179.

The Editors of Encyclopaedia Britannica. "urea". Encyclopedia Britannica, 20 Feb. 2025, https://www.britannica.com/science/urea. Accessed 16 March 2025.

https://wongchemistry.weebly.com/uploads/5/1/3/6/5136424/urea_calorimetry_lab_absent_version.pdf Used for energy and temperature calulations

I am thanking the following people for helping my complete my project:

• My Mother, For helping me with design and materials.

• My Father, for assisting in the procedure and recording.