TEMPERATURE AND HEAT

1. TEMPERATURE AND HEAT

2. Chapter 5 Temperature and Heat

3. OBJECTIVES • 1. Define the following terms: steam point (boiling point), ice point (freezing point) • 2. Define the term temperature. • 3. List the three temperature scales used domestically • 4. Be able to write the equation for each of the temperature scales and be able to apply them to make temperature conversions between the three scales.

4. 5. Define or describe the term heat and give the units in which it is measured in both mks and fps systems. • 6. Define the terms joule and calorie. • 7. Define the terms specific heat and differentiate between the terms specific heat and heat capacity. • 8. Define: latent heat of fusion and latent heat of vaporization.

5. 9. Define thermodynamics and state the three laws of thermodynamics. • 10. List and describe the three states of matter. • 11. List three assumptions of the kinetic theory. • 12. List and describe the three ways in which heat can be transferred from one place to another.

6. TEMPERATURE • The relative measure of hotness or coldness • Molecular level depends on kinetic energy of molecules • Temperature is the measure of the average kinetic energy of the molecules of a substance • Not a measure of HEAT

7. Thermometer • 1.An instrument that measures temperature changes • 2.measures thermal expansion of materials which expand with increase in temperature • 3.Bimetallic strips -one side expands more • can be calibrated to measure temp.

8. This thermostat has a coiled bimetallic strip that expands and contracts with changes in the room temperature.

9. A mercury in glass thermometer registers a change in temperature because of • Thermal expansion

10. Liquid in glass thermometer • Usually mercury or alcohol • reference points-ice point (freezing) • steam point (boiling

11. Figure 5.2Temperature Scales

12. Celsius scale oC • 0 freezing • 100 boiling • 100 units between 0 and 100

13. Fahrenheit scale oF • 32 Freezing • 212 boiling • 180 units between 32 and 212

14. Kelvin scale K • K= C + 273 • 273 freezing • 373 boiling

15. Conversion of temperature • K=C + 273 • F=9/5 C + 32 1.8 C + 32 • C=5/9(F-32) F-32 /1.8

16. HEAT • Heat is a form of energy • A. Heat is energy transferred from or to an object as the result of a temp. difference • 1. Total energy=work done + heat • E=W+ H • The total internal energy of a substance is referred to as heat

17. CALORIE • The amount of heat necessary to raise 1 gram of pure water by 1 degree C at normal atm pressure • 1 calorie=4.18 Joules • 1 kilocalorie=amt of heat to raise 1 kg of water 1 degree C 1C=1000c • diet calorie=1 kilocalorie or a big C • A “big” calorie is the food calorie • BTU=amt of heat to raise 1lb of water 1F

18. Specific Heat • When heat is added temp increases • example iron and aluminum • more energy is needed to raise temp of aluminum , more energy goes into potential energy rather than kinetic • Specific heat is the amount of heat necessary to raise the temp of 1kg of sub by 1 degree C Cp water=1Kcal/Kg C

19. S p e c i f i c H e a t • T h e a m o u n t o f h e a t n e e d e d t o c h a n g e t h e t e m p e r a t u r e o f o n e g r a m o f a s u b s t a n c e 1 o C .

20. The greater the specific heat the greater the heat required to raise the temp of that sub • Heat=mass x temp change x specific heat • H=(m) ( T)(Cp)

21. Specific Heat • How much heat is required to heat a bathtub full of water (80kg) from 12 C to 42 C • H=m T Cp • 80 x 30 x 1 = 2400

22. H e a t C h a n g e

23. H e a t C h a n g e • A s a s u b s t a n c e c h a n g e s f r o m o n e p h a s e t o a n o t h e r , t h e r e w i l l b e a c h a n g e i n h e a t e n e r g y b u t N O t e m p e r a t u r e c h a n g e .

24. H e a t C h a n g e • T h i s h a p p e n s b e c a u s e a l l t h e e n e r g y i n t h e s y s t e m i s b e i n g u s e d t o c h a n g e t h e p h a s e a n d n o t t o c h a n g e t h e s p e e d o f p a r t i c l e m o t i o n .

25. M e l t i n g P o i n t • T h e t e m p e r a t u r e a t w h i c h a s u b s t a n c e c h a n g e s f r o m t h e s o l i d p h a s e t o t h e l i q u i d p h a s e .

26. F r e e z i n g P o i n t • T h e t e m p e r a t u r e a t w h i c h a s u b s t a n c e c h a n g e s f r o m t h e l i q u i d p h a s e t o t h e s o l i d p h a s e .

27. B o i l i n g P o i n t • T h e t e m p e r a t u r e a t w h i c h a s u b s t a n c e c h a n g e s f r o m t h e l i q u i d p h a s e t o t h e g a s p h a s e .

28. Latent Heat • How much heat is required to change .2kg of ice at 0 C into water at 2 C • Heat=mass x Hf + (m x T x Cp) • ( .2)(80) + (.2)(2)(1) =16.4 kcal

29. H e a t o f F u s i o n • T h e a m o u n t o f h e a t n e e d e d t o c h a n g e o n e g r a m o f a s u b s t a n c e f r o m t h e s o l i d p h a s e t o t h e l i q u i d p h a s e . • T h e H f u s o f w a t e r i s a b o u t 8 0 c a l o r i e s / g r a m .

30. H e a t o f V a p o r i z a t i o n • T h e a m o u n t o f h e a t n e e d e d t o c h a n g e o n e g r a m o f a s u b s t a n c e f r o m t h e l i q u i d p h a s e t o t h e g a s p h a s e . • T h e H v a p o f w a t e r i s a b o u t 5 4 0 c a l o r i e s / g r a m .

31. H e a t i n f o r m a t i o n a b o u t w a t e r • W a t e r - H fus = 8 0 c a l / g • W a t e r - H vap = 5 4 0 c a l / g • I c e - C P = 0 . 5 c a l / g . C O • W a t e r - C P = 1 c a l / g . C O • W a t e r V a p o r - C P = 0 . 2 5 c a l / g . C O

32. Figure 5.5Graph of Temperature Versus Heat for Water

33. Kinetic theory of gases • All matter is made of atoms (molecules) in motion • The motion of the molecules is determined by the temperature • Random collisions occur with each other and the walls of the container

34. Phases of Matter • Solid -molecules vibrate at fixed points • liquid-molecules are free to move assume the shape of the container • Gas-molecules move rapidly, no definite shape, assume shape and volume of container • plasma-electrically charged particles of high energy

35. Heat engine is a device that converts heat into work. • Gasoline engines, steam engines • heat in=work + heat out • Thermal efficiency= work out x 100 • heat input

36. Thermodynamics • The flow, production,conversion of heat into work • First Law of thermodynamics • First law-heat added to a closed system goes into the internal energy of the system

37. 2nd law • Second Law--nothing is 100 % eff. • Heat will be lost • impossible for heat to flow from a colder body to a hotter body

38. Third law--it is impossible to obtain a temp. of absolute 0

39. Entropy • Entropy is a measure of the disorder of a system. • When heat is added entropy increases molecules become disordered • systems left to themselves tend to become disordered • The entropy of an isolated system never decreases 2nd law

40. Figure 5.8Conduction, Convection, and Radiation

41. Heat transferConduction • Conduction-transfer of heat by molecular activity. Thermal conductivity is the ability of solids to conduct heat. • Thermal insulation- liquids and gases are poor thermal conductors

42. Convection • Convection- the movement of a substance or mass (fluids and gases) from one position to another • home heating system

43. Radiation • Radiation--transfer of heat energy through space by electromagnetic waves • Can travel through a vacuum • Sun • Heat lamps

44. Figure 5.17Schematic Diagram of a Heat Engine

45. Heat pumps • Heat pump is a device that uses work input to transfer heat from a low temperature reservoir to a high temperature reservoir. • The reverse of a heat engine • refrigerators and air conditioners • home heating extracts heat from outside

46. Figure 5.19Schematic Diagram of a Heat Pump