Wait, Wait, Dont Eat Me

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Wait, Wait, Dont Eat Me!
David Chan Roycemore School Evanston, IL

• Counting Calories in the Chemlab.

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Dust off those CBLs.

• A low-cost alternative to PASCO that you may
  already possess.

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Wait, Wait, Dont Eat Me!

• Counting Calories in the Chemlab.

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Concepts

• Chapter 16 - Thermodynamics
• sections 16.1-16.4
• energy capacity to do work
• units of energy Joules, calories,
  kilocalories/Calories
• temperature average KE of particles in sample
• specific heat heat energy needed to raise temp
  1g/1
• enthalpy/change in enthalpy total energy of
  system/change
• heat transfer, Hesss Law

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• Inquiry Standards
• 11.A.4a-5c, 11.A.4e-5e
• Content Standards
• 12.C.3a,12.C.4a
• Technology Standards
• 13.A.4b, 13.B.4b,13.B.4e,13.B.5e

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Energy from Food

• Most of the food that we eat is converted into
  energy that we use to sustain our life.
• Daily activities all need/use energy to function.
• No food no energy
• Getting energy out of the food
• multistep process, digestion, metabolism
• recall principles from Biology class
• overall energy change can be determined
• determine overall enthalpy change of foods

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Types of Nutrients

• Carbohydrates
• about 60 of diet
• sugars, starch
• Fats
• 30-40 of diet
• energy storage
• Proteins
• 10 of diet
• very large molecules, made of amino acids

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How can we calculate the energy content of food?

• In Real World
• On food labels, energy measured in Calories

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How can we calculate the energy content of food?

• In Chemistry
• SI units of energy is the Joule (J)

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How can we calculate the energy content of food?

• Making Connections
• Measuring energy in Calories
• 1 cal 4.184 J
• 1 Calorie 1 kcal 4,184 J (4.184 kJ)

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How can we do it in a chemistry experiment?

• Heat Transfer
• cannot directly measure heat, can measure
  temperature change
• system vs. surroundings
• heat lost by system heat gained by surroundings
• exothermic reactions
• heat gained by system heat lost by surroundings
• endothermic reactions
• calorimetry
• minimizes amount of energy lost outside of system
  and surroundings

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Determining Heat Transfer

• What do you need to know?
• Mass
• measured in grams
• Specific Heat
• which liquid?
• Water 4.18 J/gC
• Change in Temperature
• initial temperature
• final temperature

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Put It All Together

• Q m C ? T
• q heat transferred
• m mass
• c specific heat
• ?T change in temperature

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Sample Problem

• Example 16-3 (page 541)
• Suppose that 100.00 g of water at 22.4C is
  placed in a calorimeter. A 75.25-g sample of
  aluminum is removed from boiling water at a
  temperature of 99.3C and quickly placed in the
  calorimeter. The substances reach a final
  temperature of 32.9C. Determine the specific
  heat of aluminum.
• Solution
• Heat gained by the water Heat lost by the
  aluminum
• Calculate heat gained by the water
• qgained mwater x cwater x ?T
• 100.00 g x 4.18 J/g C x (32.9 C - 22.4 C)
  4390 J
• Heat lost by the aluminum 4390 J
• 4390 J maluminum x caluminum x ?T
• 75.25 g x caluminum x (99.3 C - 32.9 C) 4390
  J
• caluminum 0.879 J/g C

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Inquiry Experiment

• Energy must be released by food. How?
• Heat lost by food when burned heat gained
  by???
• Working backwards to determine the amount of
  energy contained in food that was released during
  burning.
• Use of materials is unrestricted, but must
  include the use of CBL units and temperature
  probes.

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Your turn...