Question

You have been asked to experimentally determine the Calorie (1 Calorie = 1000 calories) 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 measure 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 inner chamber of the calorimeter that can withstand great increases in pressure.

1.What would happen to the coffee cup if you used it for a combustion reaction?

Hint: For automatic grading purposes, limit your answer to one word.

2. While using a coffee cup calorimeter for a combustion reaction, water in the reaction would ___________ ["not matter", "be a problem"] . This is because water ___________ ["would also need to be burned", "would absorb the energy from the reaction"]         .

3.The main ingredient in the desserts you will be studying is sugar or sucrose. Look up the SDS for sucrose. Name one type of fire extinguisher should you have/use if the fire (combustion reaction) gets out of hand?

Hint: For automatic grading purposes, limit your answer to a single type of fire extinguisher. Do not include "fire extinguisher" or anything to that effect in your answer.

Answer 1

Ans. 1. Explode.

The bomb of a bomb calorimeter is a thick walled (around 1.0 cm thick wall) vessel (capacity around 250 mL) made of specific alloy, that can withstand extreme pressure and heat produced during combustion.

A coffee cup calorimeter can’t withstand such with pressure and most likely to explode in combustion is carried out (theoretically) in it.

Ans. 2. Be a problem.

In the bomb, sample to be ignited is placed and filled with excess O₂ at high pressure for complete combustion- it does NOT have traces of water. The surrounding medium around the bomb is filled with water, that absorbs heat from hot bomb during combustion till thermal equilibrium is attained. Increase in water temperature in recorded and calculations are made as usual.

Presence of water as the medium in coffee cup calorimeter is not suitable for combustion i.e. combustion can’t be carried out in water as medium.

Ans. 3. CO₂ fire extinguisher.

CO₂ fire extinguisher works by isolating the combusting surface from O₂. In absence of O₂ , combustion ceases the moment all previously present O₂ is consumed up.