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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.

Chapter two

  • 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?