1/28/09 Calorimetry of Fuels and the Use of Energy to Do Work The Energy-Work Connection This experiment will be done on February 2nd & 3rd, in place of “The System” experiment. Adapted by Caitlin Conn and Patrick Crooks from The Chemurgy of Peanuts by Genevieve Miller2 Introduction NOTE: If you are allergic to peanuts, please inform your instructor or TA immediately so that you can be assigned a different lab. Energy is crucial to the survival of every living thing. As humans, our bodies need to remain within a relatively narrow temperature range. We “burn food” (internally) to stay warm. Additionally, because all systems tend to move toward disorder without an input of energy, we would die without food. We need bodily fuel so that we can function, and we burn it when we walk, talk, sleep, exercise, and study. You may have heard of “burning calories” in reference to exercise. Please note that calories are never burned. A calorie is simply a measure of energy, and that energy is actually released during a combustion reaction. During exercise, the body burns food to release energy, and that energy can be measured in different units, such as calories. Combustion reactions take place within our bodies when we burn food. A combustion reaction is defined in Chemistry: The Central Science as “[a] chemical reaction that proceeds with evolution of heat and usually also a flame.” This textbook goes on to say that most combustion reactions involve oxygen (1). Different fuels can be burned to release energy. Food, for example, is a type of fuel burned by the body. Another type of fuel with which you will use in this experiment is paraffin. Paraffin is the material of candles. When you burn a candle, the paraffin is combusted, and heat is released. The energy released by paraffin combustion can be used to light or heat areas of different sizes, depending upon how much paraffin is combusted. You will be determining the energy released by the combustion of paraffin as part of this lab. You will also examine the calorie content of a common food item, peanuts. If you have a peanut allergy, please tell your instructor or your TA right away so that you can be assigned a different makeup lab. Peanuts are used in a variety of different food items, and also in substances like cosmetics and paint. George Washington Carver was largely responsible for identifying the many different uses of peanuts and for using peanuts to serve many different purposes (2). To calculate the energy content of different substances, you will be building your own calorimeter out of household items. A calorimeter is defined as “an apparatus that measures the evolution of heat” (1). You will burn several substances and use temperature changes in water to determine the energy released by the combustion. Then you will answer theoretical questions to help you understand the connections between calories and work. You will need to use the textbooks provided for you in your classroom in order to complete some parts of this lab. Please make sure to cite these sources properly.3 Background Chemistry Overview The metabolic reactions that take place inside our body are vital to our existence. One of the most fundamental examples of metabolism is digestion. The process of digestion is most certainly a chemical one – it is an example of a combustion reaction: food reacts with oxygen to generate energy. Foods produce the same amount of energy whether they undergo combustion under metabolic conditions or they are burned outside the body. We can, then, calculate the energy value of food by burning it and measuring the amount of heat that is released from the reaction. To ensure accuracy, chemists use calorimeters, devices that measure temperature changes from chemical reactions, to determine the energy produced by a reaction. Food energy is measured in Food Calories (with a capital “C”). One “Food Calorie” is 1000 times bigger than a “scientific calorie” – that is, 1 Cal = 1 kcal = 1000 cal. One calorie is the energy required to raise the temperature of 1 g of water by 1 °C from a standard temperature at 1 atm pressure. Throughout this lab, we will use Calorie with a capital “C” to indicate Food Calories. In this experiment, you will measure the amount of energy released by the combustion of several different fuels. The energy released during the combustion will raise the temperature of a measured volume of water in a simple calorimeter. We can determine the exact amount of energy released because we know the specific heat of water. The specific heat of water is 1.0 cal per g per °C, or 1 Cal per kg per °C. By measuring the temperature change in a known mass of water, you can determine the amount of energy. Energy released = (mass of H2O heated) * (temperature increase) * (specific heat of H2O) (Eqn. 1) (2) Paraffin Calorimetry Paraffin can be burned to release energy. Typically, the energy content of paraffin, which is found in candles, is 10.0 k cal/g (3). Another word for paraffin is “alkane,” which is a particular type of organic molecule. Just as there are many alkanes, there are many different kinds of paraffin. Most paraffins are not very reactive at room temperature and one atmosphere pressure, but they can be combusted by increasing temperature and/or pressure. Paraffin combustion produces water and carbon dioxide and releases energy (4). Besides being used in candles, paraffin was being considered as a potential rocket fuel as of 2003. NASA noted the increased safety and decreased pollution that would result from using paraffin as an energy source (5). Paraffin is also used as a cosmetic and is frequently applied to the skin to soften it.4 Peanut Calorimetry Peanuts are known for their high energy value. On average, a peanut contains 6 Cal per g of energy. In fact, one pound of peanut butter contains the same food energy found in 32 eggs or 2.5 pounds of steak. It is this energy value and the low cost of producing peanuts that led Carver to stress their importance during the Depression. Peanut oil can be represented by the following molecule with molecular formula C57H104O6. Please note that at each vertex, carbon and hydrogen are present. Each vertex represents one carbon, and hydrogens are attached so that each carbon has four bonds. Figure 1. The molecular structure of peanut