1. Unit 09
Thermochemistry

2. Unit 9 Vocabulary
Thermochemistry - concerned with heat changes that occur during chemical reactions
Energy- capacity of an object to do work or produce heat
Kinetic energy- the energy an object has due to its motion
Potential energy- stored energy
Temperature- describes amount of motion of particles

3. Unit 9 Vocabulary
Heat - describes amount of energy transferred from one object to another
Endothermic process- heat absorbing process
Exothermic process- heat releasing process
Specific heat- Amount of heat it takes to raise 1g of a substance by 1°C

4. The Flow of Energy
Heat is transferred from one object to another. 4

5. Cranking up the Heat: Basic Thermodynamics
Energy is required in all biological and chemical processes.

6. Kinetic Energy Potential Energy
the energy an object has due to its motion
Potential Energy
stored energy

7. Energy in the universe is constant, though it changes forms.
Law of Conservation of energy – energy can neither be created nor destroyed

8. Heat vs. Temperature Temp. and heat are not the same thing.
Temp. describes amount of motion of particles
Heat describes amount of energy transferred from one object to another

9. Describing Energy Changes
Heat flow is from the warmer to the cooler object
Heat Flow
Heat Flow 9

10. Describing Energy Changes
Hot day 50°C = 122°F
Energy transferred from fire to beans. Change in energy for beans would be positive.
Beans lost energy, it was transferred to its surroundings. This change of energy would be negative change = ∆

11. Describing Energy Changes
Endothermic reactions – absorbs heat, ∆E is positive, the surroundings cool down
Exothermic reactions – releases heat, ∆E is negative, the surroundings heat up
Heat
Surroundings
Surroundings
Heat 11

12. Units used to describe Energy:
calorie – called “little calorie” – (cal)
kilocalorie – called “Big calorie”- (CAL)
1000 calories – same as a food calorie
Joule – the SI unit of heat - (J) 12

13. CONVERSION FACTOR
1 cal = joules
1 cal J
4.184 J 1 cal 13

14. Heat Units: Conversion Problems
1. Convert 32.7 cal to joules.
2. Convert 6.24 J to cal. 14

15. Specific Heat -
Amount of heat it takes to raise 1g of a substance by 1°C
Metals have a low specific heat
Water has a high specific heat 15

16. Learning Check
1. On a sunny day, the concrete deck around an outdoor swimming pool becomes hot, while the water stays cool. This is because… A. The deck has a higher specific heat than the water B. The deck has a lower specific heat then the water C. Both objects have the same specific heat

17. Learning Check
2. Two objects are sitting next to each other in the sunlight. Object A gets hotter than object B. A. Object A has a lower specific heat than object B B. Object A has a higher specific heat than object B C. Both objects have the same specific heat

18. 4.18 J/g × °C 1 cal/g × °C or Specific Heat of Water
Matches definition: Amount of heat it takes to raise 1g of a substance by 1°C
4.18 J/g × °C or
1 cal/g × °C 18

19. Formula for Specific Heat
q = mc ΔT
q = amount of heat – measured in cal or J
m = mass – measured in g
C = specific heat – units are J/g x °C or cal/g x °C
ΔT = change in temp – measured in °C 19

20. Specific Heat Problems:
1. Aluminum has a specific heat of J/g × °C. How much heat is lost when a piece of aluminum with a mass of g cools from a temperature of 415.0°C to a temperature of 22.0°C?
calories of heat are applied to a 250 g sample of liquid water with an initial temperature of 13.0 °C. 
Find: a) the change in temperature and
b) the final temperature. 
(remember, the specific heat of liquid water, in calories, is 1.00 cal/g x °C.) 20

21. Specific Heat Problems:
3. The temperature of a sample of water increases by 69.5 °C when 24,500 J are applied.  The specific heat of liquid water is 4.18 J/g x °C.  What is the mass of the sample of water?
4. When 34,700 J of heat are applied to a 350 g sample of an unknown material the temperature rises from 22.0°C to 173.0°C.  What must be the specific heat of this material? 21

22. Bell Work - Wed 1/23/08
When 34,700 J of heat are applied to a 350 g sample of an unknown material the temperature rises from 22.0°C to 173.0°C.  What must be the specific heat of this material?

23. Energy and Change of State
You do not have to write this
When energy is added to a solid substance, its temperature increases until its melting point is reached. Upon the addition of more energy, the substance begins to melt.
 The temperature remains the same until all the substance has melted. **** 23

24. Enthalpy of Fusion (DHfus)
Energy required to melt 1 gram of a substance at its melting point
Heating Curve: ( For Water)
Temp
DHfus
Melting point
(°C)
-10
Heating Ice
(solid)
-20
Time 24

25. Energy and Change of State
After the substance melts and if heating continues, the temperature will continue to rise until it reaches its boiling point.
۞The temperature remains the same until all the substance has boiled.*** 25

26. Enthalpy of Vaporization (DHvap)
Energy required to vaporize 1 gram of a substance at its boiling point
DHvap
Boiling Point
100
Temp
DHfus
Heating Water
(liquid)
Melting Point
(°C)
-10
Heating Ice
-20
Time

27. ► Important Formulas to Know ◄
When a substance is being heated, use the following formula: (inclined line)
q = (m)(c)(DT)
When a substance is melting or boiling, use the following formula: (flat line)
q = (m) (DHfus or DHvap) 27

28. q = (m)(c)(DT) (C) = Specific Heat: - of ice = 2.06 J/g x °C
- of water = 4.18 J/g x °C
- of steam = 2.02 J/g x °C 28

29. DHfus = 334 J/g DHvap = 2260 J/g q = (m) (DHfus or DHvap)
Enthalpy Values for Water:
DHfus = 334 J/g
DHvap = 2260 J/g 29

30. Learning Check: 30

31. Sample Problem #1 How much heat is required to melt 5.67g of ice?
Q = (m)(ΔH fus)
Q = (5.67g)(334 J/g)
Q = 31

32. Sample Problem #2
How much energy is required to boil 85g of water? 32

33. Sample Problem #3
How much energy is required to raise the temperature of 25g of water from 15°C to 75°C ? 33

34. Sample Problem #4
How much energy is required to convert 40g of ice at -10°C to steam at 150°C ?
Use Both Formulas
Draw a graph 34

35. Sample Problem #5
What is the final temperature when 1250 J of energy is added to 15g of water at 25°C ? 35

36. Warm Up How much energy is required to boil 50 grams of water?
What is the final temperature when 2500 J of heat is added to 35 grams of water at 15 degrees Celsius?
How much energy is required to convert 75 grams of ice at -20 degrees Celsius to steam at 125 degrees Celsius? (Hint: This problem has 5 steps!!) 36