Calorimetry

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Calorimetry

A Simple Experiment - Burning a Potato Chip

Using simple equipment, we can set up and measure the heat given off in a combustion reaction. If we place 100 grams of water in an aluminum can, and suspend it above a burning potato chip, the heat evolved from the chip will transfer to the water in the can. By measuring the increase in temperature of the water, we get a good idea of the amount of energy released from the potato chip. Measuring the mass of the potato chip before and after it burns, will allow us to calculate the energy released in calories per gram of potato chip.

Can Calorimetry

Mass of Chip Before Burning 2.51 grams
Mass of Chip After Burning 2.38 grams
Mass of Chip Burned .13 grams
Final Temperature of Water (degrees Celsius) 31.4
Initial Temperature of Water (degrees Celsius) 26.2
Change in Temperature (degrees Celsius) 5.2
Mass of Water in Can 100 grams

Calculating Calories in a Potato Chip

If we apply the data collected in our experiment and use the specific heat of water, we can calculate the number of calories of heat absorbed by the water.

Specific Heat Equation 3

Recall that "q" represents the heat energy measured either in joules or calories. "m" is the mass of the object heated; for our experiment "m" is the mass of the water: 100 grams. "c" is the specific heat of the substance heated. We are heating water, so the specific heat is 1 calorie per gram per degree celsius. "ΔT" is the change in temperature. The water heated up from 26.2 degrees to 31.4 degrees. The difference, final temperature minus initial temperature, is 5.2 degrees.

Calorie Calculation

We found that the energy collected from the burning chip measured at 520 calories. If we compare the mass of the chip burned to the number of calories collected we can calculate the number of calories per gram of potato chip.

Calorie Calculation

According to our experiment, there are 4000 calories in 1 gram of a potato chip. Now, for those of us who have ever tried to lose weight, or count calories, 4000 calories in 1 gram of a potato chip sounds way to big. Remember that a nutritional calorie is 1000 times larger than the calories we measured. Let's convert our measurement into nutritional calories.

Calorie Calculation

A quick look at the nutritional information for a Pringles potato chip shows that 1 serving provides 160 Calories (capital C - Nutritional Calories). 1 serving is 28 grams. That amounts to 5.71 Calories per gram of chips. From our experiment we only calculated about 4 Calories per gram of chips. We are in error by nearly 30 percent. What did we do wrong?

Calorie Calculation

In our experiment, the burning chip is situated below the can. Much of the heat released travels up toward the can, but there is a lot of heat that is not transferred to the water.

The Bomb Calorimeter - Improving our Experiment

Imagine if we could ensure that all the energy from our burning chip entered the water. If we apply a little ingenuity and some engineering principles we can collect nearly all of the energy released. The the problem is solved through the use of a bomb calorimeter.

Bomb Calorimeter

As shown in the diagram, the chip is in a container completely surrounded by water. Any heat leaving the chip will make its way to the water. The outer container is insulated to ensure the heat stays in the water. The efficiency of our measurements would be greatly improved.

Watch the following video to see an example of a calculation involving a bomb calorimeter.