Cooling/Heating Pad Chemistry Question

Question

Hi I need help with someone to check if I have solved the following correctly :) Thanks in advance

Question

An cooling pad or heating pad in "pocket format" can conceivably consist of a plastic bag divided into 3 partitions. When the pad is squeezed hard enough, the partitions break apart and the solid X is mixed with water and dissolved.

X (s) + H2O -----------> X (aq)

ΔH = +58 kJ / mole X

Data available: 0,1 moles of solid X is in total available in one each pad. The volume of the water in the pad is 0,1 dm^3. Assume that the volume does not change when X is mixed with the water.

a) Is the mentioned pad a heating or cooling pad?

b) The partitions containing contents has been at room temperature (20 ° C) before use. Calculate the temperature change when the partitions are broken. The solution formed has a density of 10.5 g / cm³. The specific heat capacity of the solution is 4.2 J / g · K. You can assume that the volume does not change when the substance X is dissolved.

c) How big would the heat change be if the pad was stored in a refrigerator (8 ° C) before it was used?

Answer:

a) It is a cooling bag. Since delta H is positive, energy is taken from the surroundings in order for the reaction to happen, therefore the surroundings will be cooler.

b) E= m*c*delta T

To calculate E i use the fact that delta H is 58 000 J/mole of X and that I have used 0.1 moles of X during the reaction. Therefore the E used for the reaction is 58 000* 0.1=5800 J

c= 4.2 J/(g*K)

To calculate m, 0.1 dm^3 solution is equal to 100 cm^3 which can be multiplied with the solutions density of 1.05 g/cm^3= 105 g

Now I have all the data needed to calculate

delta T= E/(m*c)

delta T= 5800/ (105*4.2)= 13.2 K

Answer to question b)= The temperature change is 13.2 Kelvin

c) It doesnt matter what the starting temperatute is?? (However it is possible for the pad to freeze, because the end temperature will be somewhere below 0, and the freezing process is exothermic, energy will be released, but I am not sure if this is something that is important to take into consideration here)

Answer 1

a) Yes, it would be a cooling pad for the reason you stated.

b) I think you need to report the ∆T in ºC even though a CHANGE in temperature is the same whether in C or K. But the question gives you 20ºC so it makes sense to report the change in ºC.

c) Agree. The heat change would be the same, but the final temperature would be different, for sure.