Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

25
Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves

Transcript of Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Page 1: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Matter and its Changes

Phases of Matter

Phase Changes

Heating and Cooling Curves

Page 2: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Phases of Matter

• A phase is a state of existence, a description of how the atoms or molecules of a pure substance are attached to each other.

• Chemistry recognizes three (3) common phases: solid, liquid, gas.

• Each of the phases has its own characteristics…

Page 3: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Solids

• Individual particles of the substance are held tightly in place by connections to many other particles

• Explains why solids have a rigid shape, definite volume, are typically crystalline, and have all free surfaces.

Page 4: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Liquids

• Connections between particles are flexible and may be broken. However, as one connection is broken, another connection between the particle and another particle will form.

• Explains why liquids will take the shape of their container (flexible connections), still have a definite volume, and only have one free surface.

• Also explains why liquids can be poured. (fluid)

Page 5: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Gases

• There are no connections between individual atoms or molecules.

• Gaseous systems do not have a definite shape, do not have a definite volume, and have no free surfaces.

• Particles are in constant motion and a gas will expand to fill all available space.

Page 6: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Phase Changes

• This is the description of an event where a pure substance in one state of existence is changed to a different state of existence.

• Solid Liquid is called “Melting”• Liquid Solid is called “Freezing”• Liquid Gas is “Evaporation” or “Boiling”• Gas Liquid is called “Condensation”

Page 7: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

How Phase Changes Occur

• Phase changes will occur when a sufficient quantity of heat has either been added (for melting and boiling) or removed (for freezing and condensation).

• Adding heat serves to weaken and/or break the connections between the particles.

• Removing heat serves to allow those connections to re-form.

Page 8: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Equations of Phase Changes

• Solid + heat Liquid(melting)• Liquid Solid + heat(freezing)

• Liquid + heat Gas (boiling)• Gas Liquid + heat (condensation)

• Notice that we do not use subtraction signs in chemistry equations describing events.

Page 9: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Melting Point

• A physical property.• Defined as the temperature at which a pure

substance will change from solid to liquid.• Is unique for all pure substances.• Is dependent upon the number, type, and

strength of the connections between the individual particles of a solid.

• The stronger the connections, the higher the melting point.

• Is exactly the same temperature as freezing point.

Page 10: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Boiling Point

• Is a physical property.• Is always higher than melting point.• Is unique for all pure substances.• Is defined as the temperature at which a pure

liquid will change from liquid to gas.• Also dependent upon the nature of the

connections between the particles of the substance.

• Is exactly equal to the temperature at which condensation occurs.

Page 11: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Phase Diagrams

• These are graphical presentations that display the different combinations of temperature and pressure that can permit a pure substance to exist in its different phases.

• While the specific details of a phase diagram will vary from pure substance to pure substance, the general pattern of all single component phase diagrams is the same for all pure substances.

Page 12: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

A Typical Phase Diagram

Page 13: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Some Definitions

• Triple Point – the specific combination of pressure and temperature that will enable a pure substance to exist in all three phases simultaneously.– It can be determined in a phase diagram as the

point at which all three lines converge.

Page 14: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Definition #2

• Boiling Point – formally defined as the temperature at which a liquid will turn to vapor (gas) when the pressure is exactly 1.0 atm (which is the same as 760 mmHg or 760 torr – there are other conversions too).

• This can also be determined from a phase diagram.

Page 15: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

The Phase Diagram for Water

Page 16: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

A Final Quick “Trick”

By drawing a straight line extending vertically from the triple point, you can correctly describe which of the three phases is the most dense for a pure substance.

Page 17: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

State and College Board Expectations

• The most common questions will ask you to describe what event will occur if either the temperature or the pressure are changed over a very specific line on the phase diagram.

Page 18: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Heating and Cooling Curves

• Graphical representations of how the temperature of a system changes as heat is added or removed through phase changes.

• It is observed that the temperature of a system remains constant during any phase change, even though heat is still being added or removed.

Page 19: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Heating Curve for Melting

Temp.

Heat added

S

SL

L

--- melting M.P.

Notice how the temperature remains constant during the phase change.

Page 20: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Cooling Curve for Condensation

G

GL

L

--- condensation

Temp.

--- Heat removed

?

Again, notice how the temperature remains constant during the phase change. Also notice that the “x” axis is measuring “heat removed” as the phase change is “downwards”.

Page 21: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

An Overall Heating Curve

A

B

C

DE

FTemp.

-- Heat added

1

23

45

Page 22: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

A Visual Slide of Phases

Page 23: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Sublimation• This is a “somewhat exotic” phase change.• In this process, a solid is changed directly

to a gas, by-passing the liquid phase. • Only a few substances will do this,

examples are dry ice (which is actually solid carbon dioxide), the element iodine, and the element sulfur.

Page 24: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Heating curve for Sublimation

S

SG

G

sublimation

temp

Heat added

Page 25: Matter and its Changes Phases of Matter Phase Changes Heating and Cooling Curves.

Some final thoughts…

• Remember that phase changes are physical changes. You will still have the “same stuff”.

• Key thought is that the temperature of the system will remain constant while the phase change is occurring – this is why the temperature stayed the same for so long in your lab.

• A final note…there is an opposite process to sublimation. In a very few cases, a gas can be converted directly back to a solid – this change is called deposition.