EXPERIMENT 15: Calorimetry Real world application You have been asked to experim

Question

EXPERIMENT 15: Calorimetry Real world application

You have been asked to experimentally determine the Calorie values of various desserts. You realize that a combustion reaction is analogous to the digestive reaction occurring during metabolism and the amount of energy released from combustion will tell us how much nutritional energy we can expect from the food. You then need to apply the principles of calorimetry to measu re the energy released by the desserts upon combustion. After some research, you discover that calorimetry of combustion reactions is performed in an instrument called a bomb calorimeter, which is shown below. The name “bomb” refers to the innerchamber of the calorimeter that can withstand great increases in pressure.

You need to convince your advisor to buy this instrument and then discuss how you will measure the calorie values of the assigned desserts, like cotton candy.

1.First, you are asked to justify your use of the expensive bomb calorimeter to measure the heat released by combustion. Give at least one reason why the cheaper coffee cup calorimeter will not work for this measurement.

2.The main ingredient of the desserts you will be studying is sugar or sucrose. Look up the MSDS for sucrose. What kind of fire extinguisher should you have/use if the fire(combustion reaction) gets out of hand?

3.Now that you’ve justified the instrument to your boss and are ready to work safely, you investigate your options more closely and notice that most “bomb” inner chambers are made of stainless steel. Stainless steel is not a good insulator but is instead a good conductor of heat. Why is the “bomb” made of this type of material and not an insulator?

4. Finally, you have purchased the bomb calorimeter and are ready toperform the measurement of cotton candy. You look into the inner chamber and the cotton candy seems to be completely

gone. Where did it go? Refer to the balanced combustion reaction for cotton candy, which is mostly sucrose (C12H22O11), in your answer.

5.Your cotton candy experiment was run in a calorimeter with 425 mL of water that started at 24.0 degree C. After combusting 2.00 g of cotton candy, the temperature of the water was measured at 41.3 degree C. How many Calories of energy will be released from metabolizing one serving of cotton candy (60.0 g)? Remember 1 Calorie=4184 J. Assume all heat from combustion transferred with 100% efficiency to the water?

Explanation / Answer

1) Bomb calorimeter is designed for measurement of calrofic values of fuels or other organic compounds

a) It is thermally well insulated due to presence of outer jackets

b) the thermomenter used in bomb calorimeter is of high accuracy (Generally we use Beckman's thermometer, can read upto 0.010C of temperature difference)

c) the energy released by combustion remains in the carlorimeter, so it gives us high calorific value or gross calorific value

2) Based on MSDS of sucrose, for small fire we should be available with dry powder and for large fire we should have Use water spray, fog or foam. We cannot use water jet

3) We use stainless steel as we want that the heat released during combustion process should cross the wall of bomb and reach to water to heat it up. The stainless stell also helps us to maintain the constant volume system

4) The candy undergoes complete combustion and has converted to CO2 and H2O

The reaction will be

C12H22O11 (s) + 12O2(g) ---> 12CO2 + 11H2O(l)

5) our cotton candy experiment was run in a calorimeter with 425 mL of water that started at 24.0 degree C. After combusting 2.00 g of cotton candy, the temperature of the water was measured at 41.3 degree C.

Solution: The mass of water taken = 425g (as density of water is 1g/mL, so volume is equal to mass)

Temperature raised = 41.3 - 24 = 17.30C

Specific heat of water = 4.184 J / g

So heat absrobed by water = Mass X specif heat x change in temperature = 425 X 4.184 X 17.3 = 30762.86 Joules

1cal = 4.184 Joules

so 30762.86 Joules = 30762.86 / 4.184 calories = 7352.5 Calories

so the heat evolved by the combustion of candy is completely absrobed by water (as mentioned)

the heat given by 2gram of candy = 7352.5 Calories

so heat given by 60grams of candy = 7352.5 X 60 /2 = 441150 calories

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