Chemistry Lab Questions (Calorimetry)

Question

Candy bar has a total mass of 75.0 grams. In a calorimetry experiment, a 1.0-g sample of this candy bar was burned in a calorimeter using 1000g of water. The temperature of the water in contact with the burning candy bar was measured and found to increase from an initial temperature of 21.2 C to a final temperature of 24.3 C.

Question 1: Calculate the amount of heat released when the 1.0-g sample burned. Use water as mass

Question 2: Convert heat in calories to nutritional calories and then calculate the energy content (fuel value) in Cal/g.

Question 3: Calculate total caloric content of the candy

Answer 1

Question 1:

q = mC∆T

q = heat = ?

m = mass of water = 1000 g

C = specific heat of water = 4.184 J/gº

∆T = change in temperature = 24.3 - 21.2 = 3.1º

q = (1000 g)(4.184 J/gº)(3.1º)

q = 12,970 J of heat released when 1.0 g sample is burned

Question 2:

1 Cal (nutritional) = 1000 cal

4.184 J = 1 cal

Using these conversion factors we can find calories (cal) and nutritional calories (Cal):

12,970 J x 1 cal / 4.184 J = 3100 calories (cal)/g

3100 cal x 1 Cal / 1000 cal = 3.1 Calories (Cal) nutritional calories/g

Question 3:

Total caloric content of the candy = 3.1 Cal/g x 75.0 g = 233 Calories (nutritional)

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It occurred to me that you could use specific heat of water (C) as 1 cal/gº instead of using 4.184 J/gº and then you wouldn't have to do any conversions of J (joules) to calories. The answer will come out the same, just a little less work.