Heating and Cooling Curves
• The heating curve is a graph which represents
how a sample changes phases. As heat is
added over time, the sample changes
temperature and phase accordingly. Thus
heating curve.
Using a full sheet of paper, make a
large scale drawing of this diagram.
Freezing and Boiling Point Graph
aka Phase Change Diagram or Heating and
Cooling Curve
This diagram shows the melting and boiling points for a crystalline
substance. Temperature is on the y- axis & either the amount of
energy absorbed/released or the time it takes for a phase change
is graphed on the x-axis.
Bottom flat line represents the melting and freezing points of the
substance.
Top flat line represents the boiling and condensation points of the
substance.
1. What is the melting point of this substance?
2. What is the boiling point of this substance?
1. Which phase exists during segment AB?
2. Which phase exists during segment BC?
Slanted lines represent a change in
temperature. Reading from left to right
indicates an increase and from right to left a
decrease.
Kinetic energy is directly related to
temperature so when temp go up so does KE.
Between the temperatures represented by points A and
B, the substance represented will exist in a solid state.
As time increases, heat is being added which causes the
particles to vibrate faster and thus have an increase in
kinetic energy and an increase in temperature.
What is
the
melting
point of
this
substance?
The temperature represented by point B is the melting point of the
substance. The flat line indicates that heat is being added
(absorbed), but the temperature is not increasing, thus there is no
change in Kinetic energy between points B and C. During the time
represented by line BC the substance is melting. At time B, the
substance is a solid. At time C, the substance will be completely
melted and thus exists only as a liquid.
The energy needed to change the substance from a solid to a
liquid is called “heat of fusion”. At Point C, the KE of the
substance begins increasing and continues to increase until
the substance reaches its boiling point, represented by point
D. Since temp is directly related to KE, the temp is also
increasing during segment CD.
What is
the boiling
point of
this
substance?
Point D represents the substance’s boiling point. At point D, the liquid
begins to boil and changes into the gaseous state. The energy needed
to change the liquid to a gas is called “Heat of vaporization”. During
segment DE the substance is in both the liquid and gaseous state. At
point E, all of the liquid has become gas and the KE begins increasing
as indicated by the positive slope of the line. Beyond point E, as temp
increases, the gaseous particles increase in speed.
What is
the boiling
point of
this
substance?
Label each segment as being either solid, liquid, gas, solid and liquid,
liquid and gas
Label each horizontal segment as either melting or vaporation
Label each horizontal segment as either freezing or condensation.
This graph can be read backwards. When reading it backwards,
energy is being released instead of being absorbed. When reading it
backwards, segment ED represents the condensation point
(substance is changing from a gas to a liquid) and segment CB
represents the process of changing from a liquid to a solid (freezing).
When reading this graph backwards, what is the freezing point of the
substance?
What is happening during segment CB?
What is the condensation point of the substance?
What is happening in terms of energy?
F
G
H
I
J
When reading this graph, what is the freezing point of the substance?
What is happening during segment HI?
What is the condensation point of the substance?
What is happening in terms of energy?
Crystalline solids will have definite melting and boiling points as
illustrated on the previous graphs. Crystalline substances have
definite melting and boiling points because those substances have
a very orderly arrangement of atoms.
Amorphous substances do not have a definite melting or boiling
point because their atoms do not have an orderly arrangement.
Examples of crystalline substances: ice, salt, alcohols, quartz,
sugar
Examples of amorphous substances: plastics, rubber, glass,
cement, tar
Crystallization and solidification can be
considered synonyms for freezing.
Sublimation is the process of changing from a solid to a
gas without going through the liquid state.
Deposition is the process of changing from a gas to solid
without going through the liquid state.
For crystalline substances melting point and freezing point
will be the same temperature and boiling point and
condensation point will be the same temperature.