1. HW # 7: Heat and Its Measurement
TEST: Thursday (10/20/16)
HW # 7: Heat and Its Measurement

2. Aim 7 : How can we calculate the amount of heat to cause a temperature change?

3. DEMO
A PAPER CUP
BUNSEN BURNER

8. What is sublimation?
Solid to Gas
CO2 (s) CO2 (g)

9. Is an endothermic or exothermic reaction?
Solid to Gas
I2 (s) I2 (g)

11. Heating Curve for Water
q =mHv
q=mC∆T D E
100 ºC
q=mC∆T
50 ºC
q =mHf C B
0 ºC
q=mC∆T
- 10 ºC A
HEAT ADDED

12. 1. Heat
Heat is energy
Some reactions absorb energy (heat) and some give off energy (heat).

13. Energy is measured in joules.
2. Units of Energy
Energy is measured in joules.
1 kilojoule = 1000 joules
1. Convert 40 Kj to joules
40 Kj x
1000 Joules Kj
= Joules

14. A bomb calorimeter
A Bomb Calorimeter

15. A foam cup calorimeter here, two cups are nestled together for better insulation

16. So…how do we measure heat?
We can only measure changes in heat (absolute heat doesn’t exist

17. 3. Measurement of Heat
The amount of heat absorbed or released in a reaction can be calculated using the following formulas: See table B and T

18. Solid, Liquid and Gas
TABLE B
q=mC∆T
4.18 _ J_
g K

19. Melting and Freezing
TABLE B
q =mHf
334 J g

20. Vaporization and Condensation
TABLE B
q =mHv J g

24. Table T: Heat
q= mC∆T

25. q= mC∆T
q= mC∆T
q= mC∆T

26. 4. How do you find ∆T? ∆T or temperature change ∆T = Tf - Ti
Tf = final temperature
Ti = initial temperature

27. Convert: 20 o C to Kelvin K = 20 + 273 K = 293 30 o C to Kelvin
∆T = Tf Ti
∆T = = 10

28. 6. Heat of Fusion (Hf) Hf 334 J/g
Amount of heat necessary to convert a given amount of a solid into a liquid. Hf
334 J/g
MELTING B C
FREEZING

29. 334 J/g

30. Table T: Heat
q= mHf

31. 7. Heat of Vaporization 100 HV HV= 2,260 J/g
Amount of heat necessary to vaporize a given amount of liquid at its boiling point.
Boiling G
Vaporization
100
Condensation L HV
HV= 2,260 J/g

33. Table T: Heat
q= mHv

34. HW # 7

35. 1. How much energy in joules is absorbed by 30 grams of water when is heated from 20ºC to 30 ºC?
DATA
q= mC∆T
Formula:
q = X
m = 30 g
∆T = 30ºC - 20ºC
= 10ºC
∆T = 303 K K
= 10 K
_J__
g ●K
C =
Table B

36. Using table T
q = m C ∆T
q = 30 g
4.18 J
g ●K X X
10 K
q = 1254 Joules

37. 9. How many joules does it take to melt 35 g of ice at 0 ºC ?
What do we mean by melt? Which formula are you going to use? Why ? HEAT OF FUSION: melting

38. Table T: Heat
q= mHf

39. 9. How many Joules does it take to melt 35 g of ice at 0 ºc?
q = mHf
q = 35 g X 334 Joules g
q = Joules

40. 8. How many joules are given off when 35 g of steam condense to liquid water?
q = mHv q = ? m = 35 g Hv = 2260 Joules g

41. 8. How many joules are given off when 35 g of steam condense to liquid water?
q = mHv
q = 35 g X Joules g
q = Joules

42. Compare question 2 and 3 and write a conclusion!

43. The temperature of a 95. 4 g piece of copper increases from 25
The temperature of a 95.4 g piece of copper increases from 25.0 °C to 48.0 °C when the copper absorbs 849 J of heat. What is the specific heat of copper?

44. C= _ q___ m x ΔT C=
849 J
95.4 g x °C

45. C= J/g .°C

47. REVIEW
____ Solid to liquid ____ Liquid to gas ____ Gas to liquid ____ Liquid to solid ____ Solid to gas ____ Gas to solid
Sublimation
Boiling
deposition
Freezing
Melting
Condensation