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Specific Heat

The energy required to effect a given temperature change in a known mass

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Measuring The Calories of Everything You Eat

Measuring The Calories of Everything You Eat

Credit: Harbor1
Source: http://en.wikipedia.org/wiki/File:Bombenkalorimeter_mit_bombe.jpg
License: CC BY-NC 3.0

To measure the amount of calories in the food we eat, one method that could be employed is known as a bomb calorimeter. By completely burning the food in a sealed container, the container heats a body of water in an insulated system. By measuring how much the temperature of the water changes by, you can determine the amount of energy present in the food.

  • Check out the procedure to use a bomb calorimeter: 


News You Can Use

  • The bomb calorimeter is a constant volume calorimeter that measures the heat of combustion. By burning the fuel or the material inside, the surrounding air is heated up and allowed to escape through an exhaust tube. As the air escapes, it heats up the surrounding water which allows one to determine the caloric content of the fuel. The bomb calorimeter can be easier understood by looking at the first law of thermodynamics, which states that the total energy of an isolated system is constant.

\begin{align*}\Delta U = Q + W\end{align*}ΔU=Q+W

  • Since no work is being done \begin{align*}(W=0) \end{align*}(W=0) and no heat is being exchanged between the calorimeter and its surroundings \begin{align*}(Q = 0)\end{align*}(Q=0), the amount of energy that goes into the water must be the amount of energy that is in the fuel. By using this method, scientists are able to accurately determine how much energy is in a given sample.

Can You Apply It?

Using the information provided above, answer the following questions.

  1. Why is the material that the bomb is made out of important?
  2. Why must the bomb calorimeter be a sealed system?
  3. What is the purpose of the water in the bomb calorimeter?

Image Attributions

  1. [1]^ Credit: Harbor1; Source: http://en.wikipedia.org/wiki/File:Bombenkalorimeter_mit_bombe.jpg; License: CC BY-NC 3.0

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