Thursday, June 28
• Section 2.4 & 2.7
– Energy and Nutrition
– Changes of state –Suggested Book Questions (Red indicates those covered in this lecture): •2.1: 1,3,5; 2.2: 9,11; 2.3: 13‐21 odds; 2.4: 23, 25,27; 2.5:
29,31; 2.6: 33‐39 odds; 2.7:41‐51 odds; EOC: 53‐83 odds, 89; CI: 1,5
•ALEKS Objective #1 Due Friday, June 29th at 10:00PM http://www.youtube.com/watch?v=3JdWlSF195Y&feature=plcp
http://www.youtube.com/watch?v=sLkGSV9WDMA&feature=plcp
Energy and Nutrition
Food
Oxygen
We can figure it out by running the same kind of reaction under controlled conditions in the lab, using a constant‐volume calorimeter.
Cell
Water
How much energy can our cells extract from a certain kind of food?
Carbon dioxide ENERGY!
The heat released in the rxn of food + O2
is absorbed by the water bath in the calorimeter.
Food Calories
• Carbohydrates
– Sugars (Biochemistry: Saccharides)
– Primary fuel for the body
– Makes up most of plant material
• Fats & Proteins
– Used once carbohydrates are burned
• Calorie (Cal)
– Reported on the nutrition labels of food
– 1 Cal = 1 kcal = 1000 cal = 4.184 kJ = 4184 J
• Measured by burning food in a calorimeter
Example
Table 2.3 Typical Energy (Caloric) Values for the Three Food Types
Using the energy values for food, determine the total Calories for 2 tablespoons of crunchy peanut butter that contains 6 g of carbohydrate, 16 g of fat, 7 g of protein.
Food Type
Carbohydrate
Fat
Protein
kJ/g
17
38
17
kcal/g
4
9
4
More Challenging Example
• A 0.50 g sample of vegetable oil is placed in a calorimeter containing a 1250. g water bath. When the oil is combusted, the temperature of the water bath increases by 3.61oC. What is the caloric value, in kcal/g, of the oil? (1 kcal = 4184 J)
Changes of State
Energy
Gas
Liquid
Solid
Temperature
Bromine Heating Curve
Right now we have solid bromine sitting on some dry ice.
When it is removed it will begin gaining heat from the surrounding air.
Heat added
Changes of State
Energy
Gas
Liquid
Solid
Melting
• Solid
– Molecules are low in energy
– Molecules vibrate but do not move around
• If you add energy
– The molecules gain some KE
– Start to vibrate more
• Melting Point (mp or Tmp)
– If you give the solid enough energy, the molecules overcome attractive forces and will change to the liquid phase.
Temperature
Bromine Heating Curve
Heat added
Changes of State
Energy
Gas
Liquid
Solid
Freezing
• As heat is removed, the molecules lose energy.
• Freezing Point (fp or Tfp) = melting point
– If enough energy is removed, the liquid becomes a solid.
Heating Curve
By now, we should have liquid bromine in the flask.
Temperature
Bromine will stay a liquid at room temperature. We must add energy to turn it to a gas.
Heat added
Changes of State
Energy
Gas
Liquid
Solid
Boiling
• Liquid
– Molecules can move freely
– Molecules sit at the bottom of a container
• If you add energy
– The molecules move faster
– The molecules begin to spread out
• Boiling Point (bp or Tbp)
– If you add enough energy, the molecules gain enough energy to break free of molecular interactions and change to a gas.
Temperature
Heating Curve
Heat added
Changes of State
Energy
Gas
Liquid
Solid
Condensation
• As heat is removed, the molecules lose energy.
• We don’t really talk about the condensation point, but it is the same temperature as the boiling point!
– If enough heat is removed, the gas becomes a liquid.
Temperature
Heating Curve
Heat added
Changes of State
Energy
Gas
Liquid
Solid
Evaporation vs. Boiling
At T < Tbp
At T = Tbp
Some molecules at the surface of the liquid have enough KE to enter gas phase, even at temperatures below the boiling point.
Molecules in the bulk liquid have enough KE that they begin to vaporize within the liquid, not just at the surface.
Vaporization occurs at the surface of the liquid only. Changes of State
Energy
Gas
Liquid
Solid
Sublimation
• Phase change from solid to gas.
• Particles on the surface of a solid gain enough energy to turn directly to a gas.
• Freeze‐dried food
– For backpackers, climbers, and astronauts
– Frozen food placed in a vacuum (no air) and the water sublimes out to form dried food that does not need to be frozen any longer.
• Reverse of sublimation is deposition
Temperature
Heating Curve
Heat added
• How much heat is required to convert 41.4 g of ice at ‐10.0oC to steam at 130.0oC?
Processes:
1. Heat ice
2. Change ice to
water
3. Heat water
4. Change water
to stream
5. Heat steam
sice = 2.11 J/g.oC Heat of Fus = 334 J/g
sliq = 4.18 J/g.oC Heat of Vap = 2260 J/g
ssteam = 2.00 J/g.oC
Processes:
1. Heat ice
2. Change ice to water
3. Heat water
4. Change water to steam
5. Heat steam
sice = 2.11 J/g.oC Heat of Fus = 334 J/g
sliq = 4.18 J/g.oC Heat of Vap = 2260 J/g
ssteam = 2.00 J/g.oC
Challenge Problem
• Do this very tricky question on your own. I will post the answer on the message board.
• You have 125 g of ethanol at 100.0oF. You add 30.5 kcal of energy to the ethanol. What is the final temperature and phase of the ethanol after this process? • Info about Ethanol that you may need:
Density, liquid = 0.789 g/cm3
Tboil = 351.5 K
Heat of vaporization = 837.0 J/g Tfreeze = 158.8 K
Heat of fusion = 107.9 J/g Specific heat, liquid = 2.440 J/g.K
Specific heat, gas = 1.650 J/g.K