Chapter 2 Notes

Report
Chapter Two
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Learning Goals
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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
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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.
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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.
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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.
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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:
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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.
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Energy and Nutrition
Caloric Values
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The caloric values of food are divided into the
three types of food: carbohydrates, proteins, and
fats.
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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
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These values can be used to calculate the
total Calories in any food item.
Caloric Values
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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.)
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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/
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True or False?
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Many “claims” by manufacturers are also
regulated.
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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:
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Chemical reactions in the body
 Maintaining body temperature
 Muscle contraction
 Nerve impulses
 And many more things
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Expending Energy
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Averages for males and females vary
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Female approximately 2200 kcal/day
Male approximately 3000 kcal/day
Metabolism Calculator
Energy expended varies as well
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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
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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
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A particular person’s diet consists of 80g of
protein, 350g of carbohydrate, and 100g of fat per
day.
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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.
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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.
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Example
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Lunch at Arby’s
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Beef & Cheddar
Curly Fries
Sprite, 16 oz
Calories (on label) / Fat / Carbs / Protein
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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.
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Arby’s Meal
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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.
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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
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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
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Specific Heat
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Substances absorb heat at different rates.
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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
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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
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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
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States of Matter
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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
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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
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Solid to Liquid transition
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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
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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.
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Change of State
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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
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Heating Curve for Water
Calculating Heat
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Phase change plus heat for warming or cooling
water.
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What amount of heat is required to change 50.g of
water at 20oC to steam at 100oC?
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What amount of heat must be absorbed to change
100.g of liquid water at 40oC to ice at 0oC?

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