1) What is the enthalpy change (in kJ) for burning 73.0 g of methyl alcohol? 2)A
ID: 772121 • Letter: 1
Question
1) What is the enthalpy change (in kJ) for burning 73.0 g of methyl alcohol? 2)A reaction that is used to propel rockets is N2O4(l) + 2N2H4(l) --> 3N2(g) + 4H2O(g). This reaction has the advantage that neither product is toxic, so no dangerous pollution is released. When the reaction consumes 10.0 g of liquid N2O4, it releases 124 kJ of heat. What is the value of ?H (in kJ per mole N2O4) for the chemical equation as written? 3)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.Explanation / Answer
part 1) 10 gm N2O4 = 10/92 =0.1087 moles , heat = =-124KJ, for 1mol dH = (-124/0.1087) =-1140.75 KJ/mol, part 2) 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
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