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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
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
  • 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
  • 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 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
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 energy1
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
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.
caloric values
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 values1
Caloric Values
  • These values can be used to calculate the total Calories in any food item.
caloric values2
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
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:
true or false
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.
expending energy
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 energy1
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
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
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 problem1
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.
  • 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 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
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)
temperature scales
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 scales1
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 scales2
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
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 heat1
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 heat2
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
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 matter1
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 matter2
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
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 state1
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
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
calculating heat
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?