(FCMT) Matter Transformations Lesson

Matter Transformations

When we cook our food, we use energy changes to complete the process. Energy is the ability to do work, and it can be found in several forms. Energy used for cooking purposes starts out as potential energy (or stored energy), and can potentially be used to do work. As we turn on the stove, that potential energy is converted to kinetic energy that involves the movement of molecules that performs work on our food. As more potential energy is converted to kinetic energy, the food becomes hotter and hotter and the food proceeds through the cooking process. From cooking a steak to boiling water for our pasta, we are using energy transformations to cook our food.

Most cooking occurs on a stove or a grill where either electrical energy or chemical energy is transformed into thermal energy. This thermal energy is transferred to the food we are preparing, and a change in the molecular structure of the food occurs. No matter how much energy we use, it is always transferred to another substance. This follows the law of conservation of energy, where energy is not created or destroyed, but can only change form. As we transfer the heat from the stove to a pot or a pan, energy is being transferred. There are several ways that energy can be transferred:

• conduction - when molecules exchange energy directly by contact
• radiation - the transport of energy through space without contact between molecules
• convection - the movement of energy in cells that move in a fluid motion within liquids, gases, and plasma.

Each of these involves heat flow where energy travels from an area with more energy to an area with less energy.

All of these methods are used to cook, heat, and warm our food so that we can enjoy a meal. When we place a pan on a hot eye of a stove, we are using conduction to transfer energy where there is direct contact between the two materials. We can also use convection to prepare a meal.

When we boil water, heat is applied to the bottom of the pot, and the water on the bottom warms faster than the water on the top. Warm water is less dense than cool water, so it rises toward the surface, causing a circulation of water in the pot. We also use radiation to keep our food warm. If you have ever been to a fast food restaurant you may have noticed a heat lamp over the burgers and fries. The heat generated by the bulb radiates through the air to the food below, keeping it warm for the next customer.

As you can see energy transformations occur when we cook our food. The energy that we use for cooking purposes does not go away; it is only converted to another form. Energy is transferred to the pan, the food that we eat, the air around the stove and to the stove itself. As this energy is transferred, it is converted to heat, and the heat is then distributed to the air around the stove as the objects cool down. Some of this energy is even transferred to your tongue when you try to eat a hot bite of food. The next time you cook a meal or eat a nice dinner think about all of the energy changes that occurred as your meal was being prepared.    

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