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# Chapter Two - PowerPoint PPT Presentation

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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• 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.

• 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.

• 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)

• 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.

• 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.

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

• 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.)

• 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/

• 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.

• 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

• 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

• 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.

• 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

• 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 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.

• 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 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.

• 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

• 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

• 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.

• 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

• 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

• 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

• 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.

• 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.

• 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

• 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.

• 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

• 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?