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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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
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.
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
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
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?