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, 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

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

35.6% 100 Cal 987

Cal 351 Fat %

53.9% 100 Cal 987

Cal 532 Carbs %

10.5% 100 Cal 987

Cal 104 Protein %

Percentages

53%

11%

36% FatsCarbsProteins

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 = m L

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?