Chapter Two Learning Goals Understand the forms of energy Calculate caloric values for food Convert temperatures between all three scales Calculate heat gained using a specific heat Describe the characteristics for all three states of matter Describe the changes in state between each phase and the energy involved Energy Work = an activity that requires energy Energy = the ability to do work All energy can be described as either potential energy or kinetic energy Potential Energy = stored energy Kinetic Energy = energy of motion Energy Converting between the two forms of energy occurs all of the time. Ex) Hooking up a battery to a portable music player – the batteries PE is converted into KE. Ex) Riding a bicycle up a hill – your KE is being converted into PE. Heat Heat is the energy associated with the motion of particles in a substance. Temperature is the measurement for heat and is proportional to the motions of the molecules in the object. Thus, a cold object has slower moving molecules and a warm object has faster moving molecules. Units of Energy SI unit of energy is called the Joule (J). A Joule is a relatively small unit, so more commonly will see kilojoules (kJ). Sitting in your chair your body is consuming approximately 7 kJ per minute. Units of Energy Older unit of energy is the calorie (cal). A calorie is defined as the amount of energy required to raise 1 gram of water by 1oC. A calorie is also a small unit, so more commonly will see kilocalories (kcal). Conversion between the two units: 1 cal = 4.184 J (exact) Energy and Nutrition A Nutritional Calorie (note the uppercase “C”) is actually a kilocalorie. Thus, 150 Calories is really 150 kcal. The Caloric content of food is determined by the use of a device called a calorimeter. The food is combusted in the “bomb” and the heat released is absorbed by the water. Energy and Nutrition Caloric Values The caloric values of food are divided into the three types of food: carbohydrates, proteins, and fats. Carbohydrate = 4 kcal/g Protein = 4 kcal/g Fat = 9 kcal/g It should be noted that these are all average values as there are many different types of carbohydrates, proteins, and fats. Caloric Values These values can be used to calculate the total Calories in any food item. Caloric Values From the label, the muffin contains 12g of fat, 31g of carbohydrate, and 5g of protein. 12g x (9 kcal/g) = 108 kcal 31g x (4 kcal/g) = 124 kcal 5g x (4 kcal/g) = 20 kcal Total = 252 kcal (amounts usually rounded to 2 sig. figs.) Uniform Labeling In 1990, the NLEA was passed to require that food labels contain certain information. % Daily Value – reflects percents based on a 2,000 Calorie diet. Good resource for finding caloric contents of foods including fast foods can be found at: http://www.nutritiondata.com/ True or False? Many “claims” by manufacturers are also regulated. Fat-free means that a product contains zero grams of fat. Light – the food must contain either half the fat, onethird the calories, or half the salt of the regular version. Serving sizes are at the discretion of the manufacturer. All carbohydrate sources should be treated the same way with respect to Calories. Expending Energy Whether at sleep or being very active, our bodies are expending energy. Energy is needed for: Chemical reactions in the body Maintaining body temperature Muscle contraction Nerve impulses And many more things Expending Energy Averages for males and females vary Female approximately 2200 kcal/day Male approximately 3000 kcal/day Metabolism Calculator Energy expended varies as well Sleeping = about 60 kcal/hr Sitting = about 100 kcal/hr Walking = about 200 kcal/hr Swimming = about 500 kcal/hr Running = about 750 kcal/hr Weight Gain and Loss Caloric Balance = Calories consumed minus the Calories expended Weight Gain occurs when former exceeds the latter. To lose weight requires that the latter exceed the former. To lose one pound of fat (454g) requires that you burn approximately 3500 Calories per week more than you consume. Example Problem A particular person’s diet consists of 80g of protein, 350g of carbohydrate, and 100g of fat per day. Total Calories = 80g x (4 kcal/g) + 350g x (4 kcal/g) + 100g x (9 kcal/g) = 2620 kcal This person sleeps 8 hours, walks 1 hour and sits 15 hours in one day. Energy expended = 8 hr x (60 kcal/hr) + 1 hr x (200 kcal/hr) + 15 hr x (100 kcal/hr) = 2180 kcal Example Problem The caloric balance = 2620 kcal – 2180 kcal = +440 kcal This person would potentially gain one pound of fat for every eight days at this rate. Assignment: Calculate total calories for an all fast food diet. Example Lunch at Arby’s Beef & Cheddar Curly Fries Sprite, 16 oz Calories (on label) / Fat / Carbs / Protein 440Cal / 21g / 44g / 22g 336Cal / 18g / 39g / 4g 197Cal / 0g / 50g / 0g Calculated vs. Label Calculated calories will not always agree with actual calories on label due to rounding issues. To find % of fat, carbohydrate, and protein – use calculated calories from gram amounts. Arby’s Meal Total Fats = 21g + 18g + 0g = 39g 39g x 9 Cal /g = 351 Cal Total Carbs = 44g + 39g + 50g = 133g 133g x 4 Cal/g = 532 Cal Total Protein = 22g + 4g + 0g = 26g 26g x 4 Cal/g = 104 Cal Total (Calculated) Calories = 351 Cal + 532 Cal + 104 Cal = 987 Cal (Actual total = 973 Cal) Percentages % Fat Percentages 351 Cal 100 35.6% 987 Cal 11% % Carbs 532 Cal 100 53.9% 987 Cal 36% 53% % Protein 104 Cal 100 10.5% 987 Cal Fats Carbs Proteins Temperature Scales Temperature is a measure of how hot or cold a substance is. Heat always flows from warmer objects to colder ones. Temperatures are usually recorded in one of three scales: Fahrenheit, Celsius, or Kelvin. Temperature Scales The Fahrenheit scale is used commonly in the USA. The Celsius scale is the metric system unit and is defined by the melting point and boiling points of pure water (0o and 100o). TC = (TF – 32) / 1.8 TF = 1.8 (TC) + 32 Temperature Scales The Kelvin scale is based on the fact that there is a minimum temperature called absolute zero. The degree units in Kelvin and Celsius are equal in magnitude, so the conversion between the two units is relatively simple. TK = TC + 273 Specific Heat Substances absorb heat at different rates. a metal frying pan heats up much quicker than a pan filled with water Specific Heat is defined as the amount of heat needed to raise the temperature of one gram of that substance by one degree Celsius. S = heat needed / (1 g x 1oC) Specific heats of various substances are given on page 53. Specific Heat To calculate the quantity of heat required use the following formula: q = m s DT; where q is the quantity of heat, m is the mass in grams, and DT is the change in temperature. ex) How many grams of heat are absorbed by 200.g of Al metal if its temperature rises from 25oC to 100oC? The specific heat of Al is 0.214 cal/goC. q = (200.g)(0.214 cal/goC)(75oC) = 3210 cal or 3.21 kcal Specific Heat ex) What mass of water could be heated from 25oC to 100oC if 3210 cal of heat are added? The specific heat of water is 1.00 cal/goC. 3210 cal = m (1.00 cal/goC)(75oC) m = 43g States of Matter Matter = anything that occupies space and has mass. There are three states of matter – solid, liquid, and gas. Each has its own unique characteristics Some aspects are similar States of Matter Solid = very strong attractive forces hold the particles in a rigid shape. Particles are very close together. Particles are not stationary – they do vibrate, but remain in fixed positions. Liquid = particles are free to flow (fluid). Particles are still fairly close together such that they have enough attractions to hold them together. A liquid has a constant volume, but takes the shape of the container. States of Matter Gas = particles move at very high speeds (fluid). Particles are very far apart and have little or no attraction for each other. Gases have no definite shape or volume – they always fill the container they are in. Gases are said to be compressible – they expand and contract easily. Table 2.7 compares and contrasts these three phases. Changes of State Solid to Liquid transition melting / freezing temperature is often called the melting point energy required for transition is called the heat of fusion (L). for water, the heat of fusion is 80 cal/g ex) How much energy is required to convert 50.g of ice at 0oC to water at 0oC? q = m L = (50.g) (80 cal/g) = 4000 cal or 4.0 kcal Changes of State Solid to Gas transition under the right conditions, a solid may go directly to the gas phase without becoming a liquid (and vice versa) this process is called Sublimation “Dry” ice or solid carbon dioxide will sublime to the gas phase. Snow and frost often go through this transition in very cold weather. Change of State Liquid to Gas transition boiling / condensation temperature that this occurs spontaneously is called the boiling point energy required for transition at the b.p. is called the heat of vaporization (L) for water, the heat of vaporization is 540 cal/g q=mL Heating Curve for Water Calculating Heat Phase change plus heat for warming or cooling water. What amount of heat is required to change 50.g of water at 20oC to steam at 100oC? What amount of heat must be absorbed to change 100.g of liquid water at 40oC to ice at 0oC?