Dissolving 4.49 g of CaCl2 in enough water to make 252 mL of solution causes the
ID: 772142 • Letter: D
Question
Dissolving 4.49 g of CaCl2 in enough water to make 252 mL of solution causes the temperature of the solution to increase by 3.77 oC. Assume the specific heat of the solution and density of the solution are the same as water?s (about 4.18 J/goC and 1.00 g/cm3, respectively) Calculate ?H per mole of CaCl2 (in kJ) for the reaction under the above conditions. Aside, the ?H per mole for dilution depends on the process. For example, more energy is released when starting with a large volume of water (infinite dilution), than when starting with a small volume of water. Why do you think this happens? (Find the heat released per gram and convert to per mole using the MM. Is the process exothermic? If, yes, then what is the sign for ?H?)Explanation / Answer
dT = 3.77 ,
water mass = 252 gm
,total mass = 252+4.49=256.49 gm
specific heat of water = 4.18 J/gmK = specifi heat of solution ,
heat released = -4.18 x 3.77 x256.49 =-4041.9 Joules ,
CaCl2 moles = 4.49/110.98 =0.040458 ,
per mole dH = (-4041.9/0.040458) = 99904 Joules
= 99.9 KJ/mol