1. CHAPTER 2
Matter and Energy

2. Energy and Change
Energy is the capacity to do some kind of work, such as moving an object, forming a new compound, or generating light.
Energy is always involved when there is a change in matter.
why does metal feel colder than wood?

3. Physical vs. Chemical
Give examples:

4. Every type of change involves energy
Sometimes energy is taken into the system
Endothermic
Sometimes energy is given off
Exothermic

5. Phase Changes and Energy
Endo or exothermic?
(partner check-in)
A. L → S
B. S → L
C. G → L
D. L → G
A&C exothermic, B&D endothermic

6. This created a law. What is it?
Law of Conservation of Energy
Energy cannot be created nor destroyed.

7. What is the difference between heat and temperature?
Heat is the energy transferred between objects that are at different temperatures.
Heat energy is always transferred from a warmer object to a cooler object.
For example, when ice cubes are placed in water, heat energy is transferred from the water to the ice.

8. Draw a Venn Diagram showing how heat and temp are alike and different

9. What is the difference between heat and temperature?
Temperature indicates how hot or cold something is.
It is the measurement of the average kinetic energy of the particles.

10. How do we express temperature?
Fahrenheit, Celsius, or Kelvin

11. Convert °C to K K= °C + 273.15°C Try! Convert 35°C to K
Convert 170K to °C

12. What does a heating curve look like?

14. How come some material heats up faster than others?
The specific heat of a substance is the quantity of energy (heat) that must be transferred to raise the temperature of 1 g of a substance 1 K.
This is why the sand at the beach is hotter than the water.
Sand has a lower specific heat

15. Energy Units
Energy is written with units of joules (J) or calories (cal).
A food Calorie (C) is actually a kilocalorie (1000 calories)
1 calorie=4.18 joules

16. Specific Heat
Formula
Q=m x Cpx T
Or Q=m C T

17. Q = m Cp T
“Q” is heat, unit- J or cal
“m” is mass, unit- g
“T” = change in temperature, (T = Tf -Ti ) unit- oC
“Cp”or “C”= Specific Heat Capacity
units: J/(g oC) or cal/(g oC)

18. How much energy is needed to raise the temperature of 0
How much energy is needed to raise the temperature of 0.55g sample of aluminum from 22 °C to 95°C.Specific heat of aluminum is 0.897J/gK

19. Calculate the specific heat of a substance if a 35g sample absorbs 48J as the temperature is raised from 293K to 313K.

21. DSJ
What is the specific heat of a 21gram sample that absorbs 1358J of heat with a 53 degree temperature change? Solve and explain how you did.

22. Latent Heat calculations

24. Calculating Latent Heat (phase changes)
Q= (m)Hfus (for melting and freezing)
Where Hfus is the latent heat of fusion
Q= (m)Hvap (for evaporating and condensing)
Where Hvap is the latent heat of vaporization

25. Check your HW answers

26. Notes
FL6 – Where’s the Heat? 26

29. Practice
How much heat is required to melt 46.5 grams of aluminum? The latent heat of fusion of aluminum is 95 cal/g.

31. How much energy does it take to vaporize 28g of water
How much energy does it take to vaporize 28g of water? How much energy will it take to warm the same water up to 55 degrees C?
(CP=4.18 J/gC, C= 75.3 J/m C,
Hfus=334 J/g, Hvap=2260 J/g)

32. Save for last!

33. Mixed heat practice
How much energy would it take to turn 235g of water(l) at 20 degrees C into steam(g)?
(Hfus of water is 80 cal/g and Hvap of water is 540 cal/g. CpH2O(l)=1 cal/g. deg)

34. Notes
FL6 – Where’s the Heat? 34

35. Now a challenge…
Calculate the specific heat of a metal when 2.6g of it absorb 112J of energy by warming from 23K to 96K.
How much total heat is required to melt 37g of ice at 0° and heat it up to 64°C? (hint: 2 Q’s are needed)

36. DSJ
How much total heat is required to melt 37g of ice at 0° and heat it up to 64°C? (hint: 2 Q’s are needed)

37. When to use the formula? Questions Involves heating/cooling ? (yes)
Q = m C T
Does it give specific heat? (Yes)
Does it involve a phase change?
Q= (m)Hfus or Q= (m)Hvap
Which one? (sliquid)
Q= (m)Hfus
It wants to know the heat for vaporizing
Q= (m)Hvap

38. Lab:Bunsen Burner Flame
The heat absorbed by the water is equal to the heat released by the metal
Qwater = mCp T Qmetal = mCp T
Qwater = Qmetal
mC T water = mC T metal
(water) (metal)

39. Calculations:
1. Calculate the change in the temperature of the water.
2. Calculate the mass of the water that was heated by the metal object.
3. Calculate the heat gained by the water.

40. 4. Calculate the temperature of the hot metal object
4. Calculate the temperature of the hot metal object.(The heat lost by the metal equals the heat gained by the water.)
5. What is the temperature of the Bunsen burner flame?

41. Results Table Change in Temp. of water Mass of water
Mass of water
Heat gained by water
Temp. of hot metal object
Temp. of burner flame

42. DSJ H20(s)H2O(g) H2O (g) H20(l)
Explain if each reaction is endo/exothermic.
Do products or reactants have more energy?
Would Q be + or – (go over delta H)?

43. Specific Heat Vs. Molar Heat
Energy it takes to raise 1g of substance 1 degree C
Q= m Cp ΔT
Cp used (J/g°C)
Mass given
Energy it takes to raise 1 mole of substance 1 degree C
Q= n C ΔT
n=moles
C used (J/mol°C)
Moles given

44. Practice problems on WS
Calculate the amount of energy needed to raise the temperature of 45.3 moles of Helium(C = 20.8 J/K • mol) from 35K to 68K.

47. Enthalpy The heat content or total energy of a sample is enthalpy (H).
Changes in enthalpy = H
H is (-) for exothermic rxns
H is (+) for endothermic rxns

48. Calorimetry
Calorimetry - the accurate and precise measurement of heat change.
The device used to measure the absorption or release of heat is called a Calorimeter

49. Calorimetry
Foam cups are excellent heat insulators, and are commonly used as simple calorimeters

51. Frito and Cheeto Calories Lab pics
Per. 4 link
Per. 1 link

53. WB practice problems
Find the mass of water that is vaporized at 100 degrees C by 29936J of energy. (Hvap=2260J/g)
13.2grams

54. Convert 29.6 calories to Joules
(4.18 J = 1 cal)
Convert 388K to degrees C
123.7 Joules
115 C

55. How much energy does it take to heat 2
How much energy does it take to heat 2.1moles of water from 29K to 129K? (C= 1cal/g K or 18cal/mol K)?
3780Cal

56. Endo or exo
Tell if endo/exo, sign of delta H, is heat a product or reactant.
R + 223J P
Endo, +, reactant, heat goes in
Liquid gas

57. What is the specific heat of a 100g substance that absorbs 3200J of heat while being heated up 75 degrees C?
.426 J/g C

58. Bonus
Calculate the total energy it would take to warm 63g of ice (H2O(s)) from -10 deg C and then melt it into liquid water at 0 deg C.
(Hfus=334J/g, Hvap=2260J/g, C(H2O(s))=2.06J/g,
C H2O(l)=4.18J/g c)