2 In a constant-pressure calorimeter, 70.0 mL of 0.340 M Ba(OH)2 was added to 70

Question

2 In a constant-pressure calorimeter, 70.0 mL of 0.340 M Ba(OH)2 was added to 700 mL of 0.680 M HCl. The reaction caused the temperature of the solution to rise from 21.35 degree C to 25.98 degree C. It solution has the same density and specific heat as water, what is delta H for this reaction (per mole of H2O produced)? A researcher studying the nutritional value of a new candy places a 5.30-gram sample of the candy inside a bomb calorimeter and combusts it is excess oxygen. The observed temperature increase is 2.24 degree C. If the heat capacity of the calorimeter is 43.60 kJ-K^-1, how many nutritional Calories are there per gram of the candy?

Explanation / Answer

Part1)

Total volume = 140 ml

density of solution given = 1.0 g/ml

mass of solution = 140 g

q = m C delta T= 140 x 4.184 x 4.63 = 2712.06 J = 2.712 KJ

moles of Ba(OH)2 = 0.07 Lx 0.340M = 0.0238 moles

moles of HCL = 0.07 L x 0.680 M= 0.0476 moles

HCl is in excess and it is so all the Ba(OH)2 is used up.
So you have 0.0238 mol of Ba(OH)2 used up. That will produce 2 x 0.0238 mol of water or 0.0476 mol of water.

del H = 2.712 KJ/0.0476 = 56.97 KJ per mole of water

Part 2)

Here 1 degree change means change in energy of 43.60 KJ

Therefore 2.24 x 43.60 = 97.664 KJ

The amount of energy was released by 5.3 grams so the energy released is - 97.664 kJ/5.3 g = -18.427 kJ/g.

ignoring -ve sign

18.427 kJ/g = 4.4041kcal/g (1 calorie = 4.184 J)

or Nutritional calories per gram are 4.4041 calorie/gram

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