Question

In a thermochemistry experiment the reaction of 0.0857 g of an unknown metal and an excess of 4.0 M HCl resulted in a 0.210 mL decrease in the volume of an ice/water mixture in an ice calorimeter. Calculate the enthalpy of this reaction per 1 g of metal reacted. Needed data: density of water at 273 K = 1.00 g/ml density of ice at this temperature = 0.917 g/mL ice enthalpy of fusion = 333 J/g -9.02 kJ -0.723 kJ +0.723 kJ +723 kJ +9.02 kJ

Can someone help me, I dont know how to approach this question. Thank you so much.

Answer 1

Density of Ice = 0.917 gm/ml

volume of ice per gram= 1/density = 1/0.917 = 1.0905 ml/gram

Volume of water = 1ml/gram

Change of volume when 1 gram of ice changes to water = 1.0905-1 ml

= 0.0905 ml

Total change in volume = 0.210 ml

Weight of ice changed to water = 0.210/0.0905 gram

= 2.320 gram

Energy released = weight of Ice to water*Ice enthalpy of fusion

=2.320*333 J

= 772.56 Joules

Mass of weight reacted to release 772.56 joule of energy = 0.0857 gram

Energy released per gram of metal = 772.56/0.0857

= 9015 Joules/gram

= 9.02 KJ/gram

AS ENERGY IS RELEASED SO SIGN OF ENTHALPY WILL BE NEGATIVE

SO H(REACTION PER GRAM) = -9.02KJ/gram

Hence answer is option A) -9.02 KJ/gram