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Chapter Two

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

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Chapter Two

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  1. 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

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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)

  7. 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.

  8. Energy and Nutrition

  9. 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.

  10. Caloric Values • These values can be used to calculate the total Calories in any food item.

  11. 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.)

  12. 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/

  13. 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, one-third 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.

  14. 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

  15. 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

  16. 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.

  17. 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

  18. 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.

  19. 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

  20. 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.

  21. 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)

  22. Percentages

  23. 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.

  24. 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

  25. 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

  26. 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.

  27. 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

  28. 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

  29. 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

  30. 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.

  31. 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.

  32. 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

  33. 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.

  34. 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 = m L

  35. Heating Curve for Water

  36. 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?

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