Question

Given the following data for each of the salts answer the questions below: KCINH.NO, Literature AH, kJ/mol 17.33 25.7 Cost salt per 2.5 kg $55.87 $106.70 LICI -37.03 $157.30 CaCl, -81.6 $119.28 Draw the below table and enter your experimental data for Heat of solution/g of salt. Calculate the cost in cents) of 10g of each salt and write in the table below. Name of Salt Heat of solution/g Cost (in cents) of 10 g of salt for of salt hot-pack or cold-pack Ammonium nitrate Calcium chloride (anhyd) Lithium Chloride Potassium Chloride Question 1: Which salt would be a better hot-pack based on the amount of heat per gram It? Similarly, identify the salt that would be a better cold-pack based on the amount of heat per gram of salt. Is the salt that you identified as the best hot-pack also the most cost effective? Use the cost per 10 g salt in the table above to determine the most cost effective salt for a cold pack and hot pack. Question 2: Clet's assume you are a manufacturer of hot-packs and cold-packs. Which salt would you choose to use to make your hot-pack and why? Which salt would you choose to make your cold pack and why? Explain your choice based on your answer from 01.

Answer 1

The heat transfer, or change in enthalpy in a reaction (qrxn), is related to the mass of the solution (m), the specific heat capacity of the solution (c), and the temperature change

(ΔΤ = Τfinal — Τinitial).

qrxn= – (m × c × ΔΤ)

The specific heat capacity of a substance is the amount of energy required to raise 1 g of the substance 1° C. The specific heat capacity of water is 4.186 J / (° C × g). In experiments conducted in aqueous solution, the specific heat capacity of water is generally used.

HOT PACK and COLD PACK

Many instant hot and cold packs function by dissolving a salt into water. As the salt disassociates, heat is either released in an exothermic reaction or absorbed in an endothermic reaction. Commercial instant cold packs typically use either ammonium nitrate or urea as their salt component; hot packs often use magnesium sulfate or calcium chloride. These reactions happen in a similar manner. When the salt is dissolved in water, the ionic bonds of the salt separate. This process requires energy, which is obtained from the surroundings.

The ions then form bonds with the water, a process that releases energy. If more energy is released than taken in, then the process is exothermic, making the solution feel warmer. If more energy is taken in than released, then the process is endothermic, making the solution feel cooler.

So we must Calculate the heat absorbed by the water for each mass of the chemical salt and the heat absorbed by the calorimeter for each mass of chemical salt. The specific heat of water is 4.186 J/° C × g.

qω = – [cω × mω × ΔΤ]

Since the experimental values are not provided so use this concept and the outline to figure it out.