Explain why your skin feels cool when a cold pack is applied and warm when a hot

Question

Explain why your skin feels cool when a cold pack is applied and warm when a hot pack is applied. When 5.0 g of KNO_3 were dissolved in 49.0 g of water at 24 degree C inside a coffee-cup calorimeter, the temperature of the resulting solution fell to 15.6 degree C. Is this reaction endothermic or exothermic Explain. Calculate the heat released or absorbed by the solution chemicals calorimeter. Calculate q_rxn for the reaction that occurred. Calculate the molar heat of reaction, delta H_rxn, in kJ/mol Usinh the CRC Handbook of Chemistry and Physics at.... find the enthalpy of solution of lithium chloride (LiCl) and potassium(KCl).Based on the heat of solution of each compound, assign them as good for a hot pack or a cold pack.

Explanation / Answer

ANSWER:

a) Sinc the temperature has dropped. it implies energy has been absorbed in the process hence the Reaction is ENDOTHERMIC.

b) qsol = m X Cp X T

m = mass of water = 49.0g

Cp = specic heat of water = 4.2J / g

T = Tf - Ti = 15.6 - 24 = -8.4oC

qsol = 49.0 X 4.2 X (-8.4) = 1.73KJ

c) In coffee cup cup calorimeter the pressure remains constant. Hence

qrxn = H

d)

KNO3(s) + H2O -------> K+(aq) + NO3-((aq)

when 5.0g of KNO3 are dissolved 1.73KJ of heat is released when 101g (MOLAR MASS OF KNO3) of KNO3 are dissolved following amount of heat will be liberated

(1.73 / 5.0) X 101 = 34.95KJ

Hence molar heat of reaction Hrxn = 34.95KJ

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