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1 Thermodynamics is the branch of science that studies the transformation of energy from one form to another. Thermochemistry specifically studies heat changes that accompany chemical reactions and phase changes. I. Energy and Its Forms A. Energy Defined the ability to do work or produce heat B. Two Forms of Energy Potential Energy (PE) Energy due to composition or position Kinetic Energy (KE) The energy of motion Chemical PE is energy stored in a substance because of its chemical composition Examples: plants, gasoline Plays important role in chemical reactions Chemical Potential Energy temperature measured as OR heat Forms of Energy Potential Kinetic KE is directly related to the motion of the atoms in a substance and its temperature Chemical Nuclear Stored Mechanical Gravitational Radiant Thermal Motion Sound Electrical Energy: Heat, Nutrients, and Enthalpy Page 1

2 The Law of Conservation of Energy states that Energy can be converted from one form to another, but it is neither created nor destroyed. II. Quantifying Thermal Energy A. Heat is thermal energy flowing from warmer objects to cooler objects; it is a way of transferring energy between objects and their surroundings. B. TEMPERATURE Measure of the average kinetic energy of particles of matter. The more heat the substance has absorbed, the more motion it has, and therefore, the higher the temperature. When substances lose energy, temperature decreases. Relative temperatures are measured by Celsius ( C) and Fahrenheit ( F) scales, whereas the absolute temperatures are measured by the Kelvin (K) scale. Temperature is an intensive property does not depend on sample size. C. FOUR UNITS FOR MEASURING HEAT The Metric System unit for heat is the calorie (cal). One (1) cal = the amount of heat needed to raise the temperature of one gram of water by 1 C. The Calorie (Cal) or nutritional Calorie is actually a kilocalorie. 1 Cal = 1000 cal So, a 60-Cal apple contains 60,000 cal. The SI unit for heat is the joule (J). 1 cal = J 1 cal J J 1 cal One kilojoule (kj) = 1000 joules Energy: Heat, Nutrients, and Enthalpy Page 2

3 Conversion Practice: Solve the following problems using dimensional analysis (bridges). Convert calories to Calories Cal How many calories are in 99 Calories? 99,000 cal How many joules are in kilojoules? 805,200 J Convert 884 joules to kilojoules kj Convert 195 calories to joules. 816 J How many calories are in 5.44 joules? 1.30 cal Convert 555 calories to kilojoules kj How many kilocalories are in 1099 joules? kcal How many calories are in 55.4 kilojoules? cal Convert 40.1 Calories to kilojoules. 168 kj D. SPECIFIC HEAT 1. Defined as the heat needed to raise the temperature of one gram of a substance by 1 C. It has units J/g C or 1.00 cal/g C. 3. The specific heat of water is eual to J/g C or 1.00 cal/g C. This value is considered a high specific heat. Energy: Heat, Nutrients, and Enthalpy Page 3

4 Specific Heat Capacity Table Values are at 25 C and 1 atm unless otherwise stated. Substance J/g o C Liuid water (0 C to 100 C) Lithium 3.56 Ethanol (ethyl alcohol) 2.44 Ice ( 10 C to 0 o C) 2.03 Steam (100 o C) 2.01 Vegetable oil 2.00 Beryllium (solid) Sodium 1.23 Air (50 C) Magnesium (solid) Aluminum Concrete (solid) Glass (typical) Granite (solid) Potassium 0.75 Sulphur 0.73 Calcium (solid) Iron/Steel Nickel Zinc 0.39 Copper Brass Strontium (solid) Sand Silver (solid) Tin Barium (solid) Mercury Lead (solid) Gold (solid) Energy: Heat, Nutrients, and Enthalpy Page 4

5 III. Heat Absorbed and Released A. Calorimetry is a procedure used to measure thermal energy in a chemical reaction. B. A calorimeter is an insulated device used for measuring the amount of heat released or absorbed during a chemical or physical process. 1. A known mass of water is placed in calorimeter chamber and the initial temperature is recorded. 2. The test sample is heated (food by burning, metals in hot water bath) and placed in the calorimeter. 3. Heat flows from the heated sample to the cooler water, and the temperature of water rises. 4. Heat transfer stops when the temperatures of sample and water are eual. 5. The final temperature of water is recorded. 6. The known masses and temperatures are used to calculate the heat released by sample and absorbed by water. C. EQUATION FOR CALCULATING HEAT 1. = cm T Variable Representation Unit The heat absorbed or released cal or J cal used for foods J used for non-foods c The specific heat cal/g C or J/g C m The mass of the substance g T The temperature change C + T temperature T temperature 2. Problem-Solving Strategy Write the heat euation. Draw a data table for variables. Substitute values for the variables. Solve for the unknown variable. Energy: Heat, Nutrients, and Enthalpy Page 5

6 3. Example How much heat is needed to raise the temperature of 10.0 g of water from 10.0 C to 15.0 C? = cm T c m T TI TF Water J = 209 J J/g C 10.0 g 5.0 C 10.0 C 15.0 C Specific Heat Practice 1. The temperature of a 5.00 x 10 3 gram block of concrete sidewalk increased by 6.00 C. Calculate the amount of heat the concrete absorbed. The specific heat of concrete is J/g C. = cm T Concrete c m T J T I = Initial temperature T F = Final temperature T = TF TI TI TF 2. The temperature of a sample of ironwith a mass of 10.0 grams has changed from 50.4 C to 25.0 C with the release of 114 J of heat. What is iron s specific heat? [Note: Rearrange the euation to solve for specific heat by isolating the variable c.] = cm T Iron c m T TI J/g C TF Energy: Heat, Nutrients, and Enthalpy Page 6

7 From Another Angle ating a balanced diet is fundamental to good health. Energy that keeps your brain and body E functioning comes from the foods you eat. Your digestive system and the cells in your body break down and gradually oxidize food to release energy that your cells can use and store. Taking in more energy than your body expends results in an increase of stored fuel and, conseuently, an increase in body mass. How can you calculate your energy expenditure and plan your caloric intake to maintain your body weight within a specific range? IV. Nutrients and Calorimetry A. Energy is released through chemical reactions during metabolism. B. Different nutrients are used as fuel for burning or as building material for body. 1. Carbohydrates are nutrients that are burned as fuel. 1 gram carbohydrate = 4.0 Cal energy 2. Building nutrients include fats, proteins, vitamins, and minerals. 1 gram fat = 9.0 Cal energy 1 gram protein = 4.0 Cal energy 3. The energy unit for measuring energy in foods is the nutritional or food Calorie cal = 1 kcal = 1 Cal C. Recall: The specific heat of water is eual to 1.00 cal/g C. D. ENERGY CALCULATION WITH FOODS 1. = cm T Variable Representation Unit c m T The heat absorbed or released The specific heat The mass of the substance The temperature change Energy: Heat, Nutrients, and Enthalpy Page 7 cal cal/g C 1. Food calorimetry problems often ask for the energy content of foods, which is expressed in Calories per gram (Cal/g). Calculate the heat transferred in calories. The mass for the heat euation is the mass of the water. Convert Calories to calories, using the necessary conversion factor. Set Calories calculated over the mass in grams of the food to determine energy content of the food sample. g C

8 Practice with Foods 1. A small piece of bread heats 150 ml of water from 25 o C to 65 o C. How many Calories are stored in the bread? [The density of H2O is 1g/mL.] Water 6000 cal = 6.0 Cal c 1.00 cal/g C m 150 g T 40 C TI 25 C TF 65 C If the small piece of bread that produced 6.0 Cal of heat energy had a mass of 10.0 g, what is the energy content, in Cal/g, of the bread? Cal/g = 6.0 Cal = 0.60 Cal/g 10.0 g energy content 2. What is the energy content of a 1.28 g sample of oatmeal that raises the temperature of 2500 g of water within a calorimeter from 25.0 C to 27.2 C? Express energy content in Cal/g. c m T TI TF Energy content: 4.3 Cal/g 3. How much energy in Calories is produced when 37 grams of sugar heat 63 grams of water from 44 C to 63 C? Express the energy content of the sugar in Cal/g Cal/g c m T 1.2 Cal TI TF Energy: Heat, Nutrients, and Enthalpy Page 8

9 D. NUTRITION LABELS ON FOODS Nutrition Facts Serving Size 1 Package (39g) Servings Per Container 12 Amount Per Serving Calories 200 Calories from Fat 90 % Daily Values* Total Fat 10g 15% Saturated Fat 1.5g 8% Trans Fat 2g Cholesterol 0mg 0% Sodium 410mg 17% Total Carbohydrate 23g 8% Dietary Fiber 1g 5% Sugars 4g Protein 4g Vitamin A 0% Vitamin C 0% Calcium 2% Iron 6% Nutrition Facts Serving Size 1 bar (28g) Servings Per Container 10 Amount Per Serving Calories 110 Calories from Fat 20 % Daily Values* Total Fat 2g 3% Saturated Fat 0.5g 3% Trans Fat 0g Polyunsaturated Fat 0.5g Monounsaturated Fat 0.5g Cholesterol 0mg 0% Sodium 80mg 3% Potassium 65mg 2% Total Carbohydrate 22g 7% Dietary Fiber 1g 4% Sugars 10g Protein 2g Recall 1 g carbohydrate provides 4 Cal of energy 1 g fat provides 9 Cal of energy 1 g protein provides 4 Cal of energy According to the nutrition label to the left, one serving contains 10 grams of total fat. How many Calories of energy will be provided by the total fat in one serving? 10 g fat 9 Cal = 90 Cal from fat 1 g One serving contains 23 grams of carbohydrates. How much energy can be provided by the total carbohydrates in one serving? 23 g carb 4 Cal = 92 Cal from carbs 1 g Calculate the heat energy that can be provided by the grams of protein in one serving. 4 g protein 4 Cal = 16 Cal from protein 1 g The nutrition label to the left is copied from a box of chocolate chunk granola bars. Respond to the following uestions using this label information. Calculate the energy, in Calories, provided by one chocolate chunk granola bar. [Use grams provided by fat, carbohydrate, and protein only.] Cal = 2 g fat 9 Cal = 18 Cal from fat from fat 1 g Cal = 22 g carb 4 Cal = 88 Cal from carbs from carb 1 g Cal = 2 g protein 4 Cal = 8 Cal from protein from protein 1 g What percentage of the calculated Calories is provided by fat? % fat = 18 Cal from fat x 100 = 16% from fat 114 Cal TOTAL What percentage of the calculated Calories is provided by carbohydrates? % carb = 88 Cal from carb x 100 = 77% from 114 Cal TOTAL carb What percentage of the calculated Calories is provided by protein? % protein = 8 Cal from protein x 100 = 7% 114 Cal TOTAL from protein Energy: Heat, Nutrients, and Enthalpy Page 9

10 Food Calorimetry Practice Follow the step-by-step process outlined in this notes packet. SHOW ALL WORK. Use 1.00 cal/g C as the specific heat of water. 1. When burned, a cheese ball will raise the temperature of 200 ml of water from 30 C to 95 C. Calculate the food Calories of the cheese ball. [Calculate the energy released and then convert cal to Cal.] 13,000 cal = 10,000 cal to 1 SF Converts to 13 Cal = 10 Cal to 1 SF 2. A bag of Cheetos contains 170 food Calories. If burned in a calorimeter with 50 ml of water at an initial temperature of 25 C, what will the final temperature of the water be? T = 3400 C TF = 3425 C = 3000 C with 1 SF 3. A Rice Krispies treat contains 200 food Calories. When burned in a calorimeter, it raises the temperature of water from 25 C to 40 C. What is the mass of the water? m = 13,333 g = 10,000 g to 1 SF Energy: Heat, Nutrients, and Enthalpy Page 10

11 V. Heat Transfer 1. In a calorimeter, heat flows from. The flow of heat stops ; energy is eual to energy. 2. In other words,. 3. Example A 125-gram sample of water is placed in a calorimeter with an initial temperature of 25.6 C. A 50.0-gram sample of an unknown metal is heated to C and is placed in the water. The final temperature of the water and the metal is 29.3 C. Write the heat euation. Draw the data table. = Place values from problem into table. Twater = Tmetal = Calculate T for water and the metal and add to table. For which substance water or metal is there enough information to use the heat euation? Solve for the unknown. Once for water is known, use heat euation to solve for specific heat, c, of the metal. Calculate heat absorbed for water: Calculate specific heat of metal: Energy: Heat, Nutrients, and Enthalpy Page 11

12 Heat Transfer Practice Follow the step-by-step process outlined in this notes packet. SHOW ALL WORK. 1. A 77.5 gram sample of an unknown metal is heated to 62.5 C and placed into a calorimeter containing 93 grams of water at 23.3 C. If the final temperature of the solid sample and the water is 26.2 C, what is the specific heat of the solid? 2. A 27.9 gram sample of an unknown metal is heated to 75 C and placed into a calorimeter containing 45 grams of water at 14 C. If the final temperature of the system (the solid sample and the water) is 26.5 C, what is the specific heat of the solid? 3. A 50.6 gram sample of iron metal is heated and put into 104 grams of 19.7 C water in a calorimeter. If the final temperature of the iron sample and the water is 24.3 C, what was the temperature of the iron sample when it was placed in the water? Energy: Heat, Nutrients, and Enthalpy Page 12

13 Energy: Heat, Nutrients, and Enthalpy Page 13