Food Energy Lab

Energy is the ability to do work. The electrons that are involved in forming molecular bonds contain energy.

If the reactants (what goes into a reaction) have LESS energy than the products (what comes out of a reaction) then energy was added.

If the reactants (what goes into a reaction) have MORE energy than the products (what comes out of a reaction) then energy was released.

This later situation is what happens when you burn something. Wood has more energy than ash, energy was released in the form of heat and light we call this “fire”.

All molecules including organic compounds such as: carbohydrates, proteins and lipids have energy. Cells using many, many steps (so that the energy released is in small enough amounts that it won’t harm the cell) break these large food molecules into many smaller, less energy filled products, typically carbon dioxide (CO₂) and water (H₂O).

Since the reactants (carbohydrates, etc.) have more energy than the products (carbon dioxide and water) energy was released. In the cell, most of the energy (60%) is released as heat but about 40% is capable of doing cellular work, this is called FREE ENERGY.

A calorie is one type of energy unit. A calorie is defined “…as the amount of energy it takes to heat 1 mL of water 1 degree Celsius”. When you see the amount of calories listed on a nutritional label it is always given in the form of kilo calories/Kcals/Calorie (capital C). A Kcal is equal to 1000 calories (lower case c).

Today’s lab is going to be measuring the amount of energy/calories in a variety of foods. This will be done by burning these foods, letting the released energy heat a known quantity of water (100 ml) and then, you will determine the change in mass of the food item and the change in water temperature. To determine kilo calories/gram, you will do the calculations given later in this lab handout.

Measurements taken in real labs would be much more accurate, probably about ten times larger than ours will be. One major reason why we will be wrong is, that not all of the heat released during the burning of the nut will actually heat the water, some (a lot) will be released into the room and not be measured by the computer probe in the water. Also our balances are not as accurate other more expensive models.