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Phases and Heat Chapters 13 & 17.

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Presentation on theme: "Phases and Heat Chapters 13 & 17."— Presentation transcript:

1 Phases and Heat Chapters 13 & 17

2 Phases of Matter Chapter 13

3 Phases There are three phases, or states, that we will discuss Solid
Liquid Gas

4 Solids form of matter that has a definite shape and definite volume.
Use (s) to denote solids in chemical reactions

5 Solids In most solids the atoms, ions, or molecules are packed tightly together The particles in solids tend to vibrate around fixed points When you heat a solid, its particles vibrate more rapidly, eventually the solid breaks down and melts.

6 Types of Solids Crystalline Solids
In a crystal the particles are arranged in an orderly, repeating, three-dimensional pattern called a crystal lattice. There are many different shapes of crystalline solids, pg 397

7 Types of Solids Non-Crystalline Solids
Amorphous solids lack an orderly internal structure. Ex – Rubber, plastic, and asphalt. Glass – transparent fusion product of inorganic substances that have cooled to a rigid state without crystallizing. Sometimes called super-cooled liquids.


9 Allotropes Two or more different molecular forms of the same element in the same physical state Different properties because they have different structures

10 Allotropes of Carbon

11 Liquids form of matter that has a definite volume, indefinite shape, and flows. Use (l) to denote liquids in chemical reactions

12 Liquids In liquids the atoms or molecules are able to slide past each other. In liquids there are intermolecular attractions between the atoms or molecules, which determine the liquid’s physical properties. When you heat a liquid the particles vibrate more rapidly and start moving past each other faster.

13 Gases form of matter that takes both the shape and volume of its container Use (g) to denote gases in chemical reactions

14 Phase Changes Six Changes Solid  Liquid Melting
Liquid  Solid Freezing Liquid  Gas Vaporization Gas  Liquid Condensation Solid  Gas Sublimation Gas  Solid Deposition

15 Phase Changes During any given phase change, both phases can exist together in equilibrium Example At 0°C, water can exist in both the liquid and solid phases in equilibrium

16 Energy When energy is added to a reaction, or phase change, it is called Endothermic When energy is released during a reaction, or phase change, it is called Exothermic

17 Phase Changes Which phase changes are endothermic, requiring the addition of energy? Melting Vaporization Sublimation

18 Phase Changes Which phase changes are exothermic, releasing energy?
Freezing Condensation Deposition


20 Phase Diagram of CO2


22 Energy What is energy? Two main types Capacity to do work
Ability to do work Two main types Kinetic Potential

23 Types of Energy Kinetic Energy Potential Energy Energy of motion
Related to the speed and mass of molecules Potential Energy Stored energy

24 Temperature How is energy related to Temperature?
What happens to the temperature of a substance when you add energy? Particles move faster Temperature increases

25 Temperature Relationship between energy, particle speed, and temperature Temperature Definition Average Kinetic Energy

26 Temperature Scales Kelvin (K) and Celsius (°C) scales
Kelvin scale is called the absolute scale Related to the kinetic energy of a substance Celsius scale is a relative scale based on the boiling and freezing points of water

27 Temperature Conversion
K = °C + 273

28 Pressure What is pressure? Physics – Force per unit area
Chemistry – related to the number of collisions between particles and container walls

29 Pressure Conversion 1 atm = kPa

30 Vapor Pressure Pressure exerted by vapor that has evaporated and remains above a liquid Related to temperature As temperature increases, vapor pressure increases

31 Boiling vs. Evaporation
Vapor pressure equals external, or atmospheric pressure Evaporation Some molecules gain enough energy to escape the liquid phase At temp. less than boiling point

32 Normal Boiling Point Boiling Point at Standard Pressure
1 atm or kPa

33 Evaporation Why is evaporation considered a cooling process?
As the molecules with higher kinetic energy evaporate, the average kinetic energy of the substance decreases

34 Table H Shows the relationship between temperature and vapor pressure for four specific substances



37 Thermochemistry Chapter 17

38 Thermochemistry Heat involved with chemical reactions and phase changes

39 Heat Energy transferred from one object to another, usually because of a temperature difference Measured in Joules (J) or calories (cal) Heat flows from hot to cold

40 Heat Transfer Endothermic Exothermic Energy being added
Energy being released

41 Specific Heat Capacity
Amount of heat needed to raise the temperature of 1 g of a substance by 1°C Unique for each phase of each substance 4.18 J/(g*°C) for liquid water Listed in Table B of Reference Tables

42 Heat What factors affect the amount of heat transferred?
Specific Heat Capacity Mass Temperature difference between objects

43 Heat Equation Heat, Q Mass, m Specific Heat Capacity, c
Change in Temperature, ΔT Q=m*c*ΔT

44 Example 200g of water is heated from 20°C to 40°C, how much heat is needed? Q = m*c*ΔT Q = (200g) * (4.18J/g°C) * (20°C) Q = J

45 Example How much energy is required to raise the temperature of 50g of water from 5°C to 50°C? Q = m*c*ΔT Q = (50g) * (4.18J/g°C) * (45°C) Q = 9405 J

46 Another Example What is the Specific Heat Capacity of Fe, if it takes 180J of energy to raise 10g of Fe from 10°C to 50°C? Q = m*c*ΔT 180J = (10g) * c * (40°C) c = 0.45 J/(g*°C)


48 Phase Change At what temperature does ice melt?
At what temperature does water freeze? Melting point and freezing point are the same

49 Phase Change What happens to temperature during phase changes?
Temperature remains constant Temperature remains CONSTANT during a phase change

50 Phase Change If energy is being added, what kind of energy is it?
Energy being added is potential energy, not kinetic energy Potential energy is being used to separate or spread the particles apart

51 Heat of Vaporization, Hv
Amount of energy needed to vaporize 1g of a substance Water = 2260 J/g Q=mHv Use for Liquid  Gas or Gas  Liquid

52 Heat of Fusion, Hf Amount of energy needed to melt 1g of a substance
Water = 334 J/g Q=mHf Use for Solid  Liquid or Liquid  Solid

53 Examples How much energy is needed to melt 10g of ice at 0°C? Q = m*Hf
Q = (10g) * (334J/g) Q = 3340 J

54 Example How much energy is needed to vaporize 10g of water at 100°C?
Q = m*Hv Q = (10g) * (2260J/g) Q = J

55 Phase Change Which requires more energy melting or vaporization? Why?
Molecules are spread farther apart as a gas It takes more energy to get gas particles spread apart


57 Heating (Cooling) Curves
Shows relationship between temperature and time during constant heating or cooling. Also shows phases, and the phase changes between them.

58 Heating Curves Diagonal lines are phases
Horizontal lines are phase changes Time (s) Temp (˚C) Gas Liquid Solid

59 Heating Curves Diagonal lines are phases
Horizontal lines are phase changes Vaporization Condensation Time (s) Temp (˚C) Melting Freezing


61 Conservation of Energy
Energy can not be created or destroyed, only transferred or converted from one form to another. Energy lost by one object must be gained by another object or the environment Qlost = Qgained

62 Example A chunk of iron at 80°C is dropped into a bucket of water at 20°C. What direction will heat flow? From the iron to the water Hot to cold

63 Example A chunk of iron at 80°C is dropped into a bucket of water at 20°C. What could be the final temperature, when they both come to equilibrium? Between 20°C and 80°C

64 Example A 100g block of aluminum, c=0.90J/g*°C at 100°C is placed into 50g of water at 20°C, what will be the final temperature when the aluminum and water reach equilibrium? Qlost = Qgained m*c*ΔT = m*c*ΔT 100g*0.90J/g°C*(100°C-Tf) = 50g*4.18J/g°C*(Tf-20°C) 90*(100-Tf) = 209*(Tf-20) Tf = 209Tf-4180 13180 = 299Tf Tf = 44°C

65 Conservation of Energy
System Work Done (Energy) Energy In Energy Out

66 Conservation of Energy
Work Done (Energy) Energy In Energy Out

67 Conservation of Energy
Metabolism Food In Waste Out

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