1. Chemical Reactions & Equations
Chemical Energy (Heat)
Thermodynamics
Dr. Ron Rusay

2. Chemical Energy (Heat)
Thermodynamics

3. Two types of thermochemical reactions:
Heat of Reaction & Heat Exchange Exo- and Endo- thermic Reactions (Exergonic and Endergonic)
reactant(s) product(s)
Two types of thermochemical reactions:
Exothermic: Heat is a reaction product; the heat flows to the surroundings. The amount is the difference between the products minus the reactants.…It is a negative value for the reaction.
Endothermic: Heat is a reactant; the heat flows from the surroundings. The amount is the difference between the products minus the reactants…It is a positive value for the reaction.

4. Temperature vs. Energy (Heat)
Temperature relates to the random motion of particles. If motion ceases, then in theory absolute zero (0 Kelvin) is possible.
Heat of reaction involves transfer of energy due to the different energies of reactants and products. Temperature is not energy, but it relates to an energy state. HOT (higher energy) cold (lower energy)

5. PIZZA &
Figure: 05-07

6. Why can you burn the top of your mouth with hot pizza just out of the oven and not the bottom? (The top & bottom are at the same temperature!!!)

7. Cp UNITS: J/(g⋅K) or J/(mol⋅K) Energy :
Cp UNITS:
J/(g⋅K) or
J/(mol⋅K)
Energy :
joule (J)
calorie (c)
kilocalorie (C)
Kilowatt hour (kWh)
Light (radiant)
Motion (kinetic)
Electrical
Chemical
Nuclear energy
Gravitational
Human Body (average) 3.470
Protein 1.700
Wood 1.700
(Cp) Body fat: In obese mice (fat content 52.76% body wt) the heat capacity is 3.66 kJ kg-1 K-1 and in lean mice (fat content 7.55% body wt) the heat capacity is 2.65 kJ kg-1 K-1.

8. Specific Heat Interactive Simulation
Human Body (average) 3.470
Protein 1.700
Wood 1.700

9. QUESTION

10. Answer
0.13 J/gC = 48.8 J / 15 grams . 25C

11. 80% of muscular physical activity energy has to be released by the body as heat. Obese people have a thick insulating fat layer.
tissue conductance as well as sweating rate are significantly lower than in lean, fit people, with total heat loss capacity possibly limited to 350 W. It is concluded that thermoregulation may fundamentally restrict exercise performance in unfit obese.
Human obesity (BMI >30) is associated with increased heat production; however, subcutaneous adipose tissue (fat) provides an insulating layer that impedes heat loss. This can be an advantage or a disadvantage depending on the surroundings. Do you know your Body Mass Index? See the NIH link below:

12. Thermoregulation: heat transfer to or from our body, and to or from the surroundings
If your core body temperature drops to below 35°C (95°F), you are 31°C (88oF) comatose, @ 26-28°C (79-82°F) arrhythmia and death
An example of the threshold at which the human body is no longer able to cool itself and begins to overheat is a humidity level of 50% and a high heat of 46 °C (115 °F), as this would indicate a wet-bulb temperature of 35 °C (95 °F).[11]

13. radiation, conduction, convection, evaporation
Thermoregulation: heat transfer to or from our body, and to or from the surroundings
If your core body temperature drops to below 35°C (95°F), you are ‘hypothermic’, 31°C (88oF) comatose, 26-28°C (79-82°F) in arrhythmia and finally death
An example of the threshold at which the human body is no longer able to cool itself and begins to overheat is a humidity level of 50% and a high heat of 46 °C (115 °F), as this would indicate a wet-bulb temperature of 35 °C (95 °F).[11]
radiation, conduction, convection, evaporation

14. FASEB J.
April 2009
596.2
80% of muscular physical activity energy has to be released by the body as heat. Obese people have a thick insulating fat layer.
tissue conductance as well as sweating rate are significantly lower than in lean, fit people, with total heat loss capacity possibly limited to 350 W. It is concluded that thermoregulation may fundamentally restrict exercise performance in unfit obese.
The relative heat capacity (Cp) of an obese person (BMI >30) is higher than that of a lean person. It has a pronounced effect on thermoregulation and cooling of the body.

15. Abdominal (left) and right-hand (right) thermograms of an obese female (A) and a normal-weight female (B).
Abdominal (left) and right-hand (right) thermograms of an obese female (A) and a normal-weight female (B). Arrows indicate the location 1.5 cm inferior to the umbilicus selected for image analysis. Temperatures are represented by colors, as indicated by the gradient on the right.
David M Savastano et al. Am J Clin Nutr 2009;90:
Increased heat production is associated with obesity; however, subcutaneous adipose tissue provides an insulating layer particularly around the abdomen, which impedes heat loss. To regulate body temperature, obese individuals must increase their heat dissipation, one way is through their hands.
©2009 by American Society for Nutrition

16. Two General Types of Energy
Potential: due to an object’s position or material’s composition - which can be converted to work
Kinetic: due to motion of an object
KE = 1/2 mv2
(m = mass, v = velocity)

17. Energy:
Heat is energy.
How many different other types of energy are included in the graphic?
UNITS:
joule (J)
calorie (c)
kilocalorie (C)
Kilowatt hour (kWh)

18. PhET/states-of-matter_en.jnlp

19. Temperature and Physical States s  l  g
Time: second
SI unit

20. Temperature and Physical States s  l  g

21. Heat @ constant Pressure (Enthalpy) H s  l  g
H2O 25 oC
H = Cp liq x mass x T H
H = ? kJ
H2 O 0 oC
Hfusion = kJ/mol
H2 O 0 oC
H = Cp ice x mass x T
H2 O 25 oC
Hfusion = ? kJ
H = ? kJ
Process Path
H = Hice +Hfusion +Hliq
If 50.0 g of -25 oC warms to 25 oC what is H of the process?
H = ?
H = ? kJ

22. Heat @ constant Pressure (Enthalpy) H s  l  g
H2O 25 oC
H = Cp liq x mass x T H
H = 5.22 kJ
H2 O 0 oC
Hfusion = kJ/mol
H2 O 0 oC
H = Cp ice x mass x T
H2 O 25 oC
Hfusion = kJ
H = 2.54 kJ
Process Path
H = Hice +Hfusion +Hliq
If 50.0 g of -25 oC warms to 25 oC what is H of the process?
H = ?
H = kJ

23. Hsolidification= (-)
Hdeposition= (-)
H = J or kJ
cal or kcal
Hcondensation= (-)
Hsolidification= (-)
f.p. oC
cooling
cooling
heating
heating
b.p. oC
m.p. oC
Figure: 05-09
Hvaporization= (+)
Hfusion= (+)
Hsublimation= (+)

24. QUESTIONs

25. QUESTION

26. Answer
A) endothermic
Hfusion= (+)

27. QUESTION

28. Answer
A) endothermic
Hvaporization= (+)

29. QUESTION

30. Answer
B) exothermic
Hcondensation= (-)

31. QUESTION

32. Answer A) endothermic Hvaporization= (+) Hfusion= (+)
Hsublimation= (+)

33. QUESTION

34. Answer
B) exothermic
Hsolidifcation= (-)

35. Heat of Reaction
The heat of any reaction can be calculated from the heat(s) of formation of products minus reactants.
Hrxn° = npHf(products)   nrHf(reactants)
Endothermic Hrxn°=(+) and Exothermic Hrxn°=(-)

36. Heat of Reaction
Endergonic Hrxn°=(+) and Exergonic Hrxn°=(-)

37. QUESTION

38. Answer

39. QUESTION

40. Answer

41. Endothermic Reactions Photosynthesis
6 CO2 (g) + 6 H2O(l) + energy C6H12O6 (s) + 6 O2(g)
Hrxn° = npHf(products)   nrHf(reactants)
Hrxn° = (+) = kJ/mol C6H12O6 (glucose or fructose)

42. Endothermic Reactions
Ba(OH)2.8H2O(s) + 2NH4Cl(s) → 2NH3(g) + 10H2O(l) + BaCl2(s)
Hrxn° = npHf(products)   nrHf(reactants)
Hrxn° = (+) = + ? kJ/mol

43. QUESTION

44. Answer Hrxn° = npHf(products)   nrHf(reactants)
Hrxn° = kJ – (-3973 kJ) = kJ/mol

45. Exothermic Reactions
Glycolysis: Food / eg. “Burning” Sugar energy (Photosynthesis in Reverse)
C6H12O6 (s) + 6 O2(g) CO2 (g) + 6 H2O(l) + energy
Hrxn° = npHf(products)   nrHf(reactants)
Hrxn° = (-) = kJ/mol C6H12O6 (glucose or fructose)

46. Calorimetry (Interactive)
How much exercise do you need to burn 1 gram of sucrose?
m x Cp x ΔT = q
1000. g H20 x J/g°C x (1.7°C) =
= J
= J J
ΔHReaction = J / g sucrose
ΔHReaction = J / g sucrose
ΔH Reaction = -15 kJ /g sucrose = kcal /g sucrose

47. Exothermic Reactions Hrxn° = - 14,455 kJ/mol

48. Exothermic Reactions Combustion: Burning Carbon Compounds
CxHyOz + (x + y/4 - z) O2  x CO2 + y/2 H2O + energy

49. Exothermic Reactions Octane (Gas) Combustion Engine
2 C8H18(l)+ 25 O2(g) CO2(g)+18 H2O(l) + energy
Hrxn° = - 5,075 kJ/mol
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50. Hot Food: MRE’s Exothermic Reaction
Enough heat to raise the temperature of 8 ounces of food to 56oC (100oF).

51. MREs: Exothermic Reaction
Mg(s) + 2 H2O(l) Mg(OH)2 (aq) + H2 (g)
+ energy:
Enough to raise the temperature of 8 ounces of food to 56oC (100oF).
MREs: Exothermic Reaction
To 56oC (100oF) from what temperature?
What is the room’s and your respective temperature?