C OLD P ACK C HEMISTRY Caroline Manion

P ROBLEM AND Q UESTION What happens when instant cold packs are activated? The purpose of this experiment was to discover which amount of ammonium nitrate (NH 4 NO 3 ) absorbs the most amount of Joules when dissolved in 100 mL of water.

B ACKGROUND I NFORMATION Ammonium Nitrate (NH 4 NO 3 ) is a solid, odorless, colorless, crystalline salt used in fertilizers and explosives. When combined with water, NH 4 NO 3 undergoes an endothermic reaction, absorbing the heat in the solution. The equation for this reaction is H 2 O + NH 4 NO 3 →NH NO 3 -. Since the ammonium nitrate undergoes an endothermic reaction, it absorbs the heat that is in the water in the form of Joules. This makes the solution cold.

B ACKGROUND I NFORMATION CONT. The equation to calculate the amount of Joules absorbed by this reaction, also known as the heat of the reaction, is q=cmΔT. Q stands for the energy in Joules C is the specific heat of the water (4.187kJ/°C) M is the mass of the solution (10.0g-50.0g) ΔT is the change in temperature.

H YPOTHESIS If five different amounts of ammonium nitrate (10.0g, 20.0g, 30.0g, 40.0g, and 50.0g) are dissolved in 100mL of distilled water, then the beaker containing the 50.0g will have the lowest average temperature after three trials, and therefore have absorbed the most amount of Joules.

M ATERIALS 5 Beakers Distilled water (100mL per beaker) Ammonium Nitrate (NH 4 NO 3 ) Temperature Probe Stirring Rod

P ROCEDURE 1. A beaker was filled with 100mL of distilled water. The starting temperature of the water was taken and recorded g of NH 4 NO 3 were measured and added to the water. 3. The solution was stirred and the temperature taken after 30 seconds. 4. Steps 1-3 were repeated for 20.0g. 30.0g, 40.0g, and 50.0g of NH 4 NO Steps 1-4 were repeated for 2 more trials of each amount.

V ARIABLES Independent Amount of NH 4 NO 3 Dependent Temperature of water after 30 seconds Constant Amount of water Amount of time the solution sat for (30 s)

D ATA AveragesBeaker 1Beaker 2Beaker 3Beaker 4Beaker 5 Initial Temp. of Water 19.5° C 19.8° C21.0° C20.9° C Temp. After 30 seconds 13.4° C8.4° C5.2° C2.9° C0.5° C Beaker 1Beaker 2Beaker 3Beaker 4Beaker 5 Heat of Reaction

D ATA

C ONCLUSION The Hypothesis was supported because beaker 5, which contained 50.0g of NH 4 NO 3 was the coldest after 30 seconds. Some sources of error were that only 3 trials were conducted due to a limited supply of NH 4 NO 3 and instances where the software to record the temperature was not started right away. Further research would include more trials and to discover at which amount of NH 4 NO 3 the heat of the reaction no longer follows a linear trend.

T HANK Y OU ! References Ammonium nitrate. (n.d.). Retrieved October 8, 2010, from Houghton Mifflin Company website: Brain, M. (2006, November 29). Cold packs. In How refrigerators work. Retrieved October 17, 2010, from Helmenstine, A. M. (n.d.). Endothermic and exothermic reactions. Retrieved October 8, 2010, from New World Encyclopedia Contributors. (2008, November 1). Ammonium nitrate. In Ammonium nitrate. Retrieved October 5, 2010, from New World Encyclopedia website: Princeton university. (2010). Heat energy. Retrieved October 21, 2010, from Princeton university website: Tissue, B. M. (2000). Reaction thermodynamics. Retrieved October 8, 2010, from Unknown. (2010, January/). Balanced equation for ammonium nitrate and water [Online forum message]. Retrieved from Weisstein, E. W. (2007). Heat capacity. Retrieved October 21, 2010, from Wolfram research website: Whyte, D. B. (2009, June 18). Cold pack chemistry. Retrieved October 17, 2010, from Wilbraham, A. C., Staley, D. D., Matta, M. S., & Waterman, E. L. (2008). Heat of solution. In Chemistry (p. 525). Upper Saddle River, NJ: Pearson Prentice Hall.