Learning Area Grade Level

W4
General Chemistry 2 12
Quarter Third Date April 19-23, 2021

I. LESSON TITLE Phase Changes: Phase Diagram and Heating Curve

II. MOST ESSENTIAL LEARNING 1. Interpret the phase diagram of water and carbon dioxide
COMPETENCIES (MELCs) 2. Determine and explain the heating and cooling curve of a substance
III. CONTENT/CORE CONTENT 1. Describe the phase diagram.
2. Differentiate the phase diagram of water and carbon dioxide.
3. Appreciate the importance of phase diagram in daily life.
4. Describe heating and cooling curve of a substance.
5. Explain the heating and cooling curve of a substance.
6. Appreciate the importance of heating and cooling curve in industries.

Suggested
IV. LEARNING PHASES Learning Activities
Timeframe
A. Introduction 90 mins In chemistry, we study water not just its properties but also the phase changes that it
Panimula undergoes. In this module, we will be very specific on interpreting the phase diagram of
water and compare it to other substances like carbon dioxide. We will be using a graph
to help you visualize more on what particular pressure and temperature they exist as a
gas, liquid, and solid. So be attentive as we discuss this topic.
Phase Change
When energy is added or removed, transformations from one phase to another will
occur e.g. a change of solid-phase having the greatest order to gas phase having the
highest randomness, or vice versa. Let us consider the phase change of water. Water
will become water vapor if heat is added up, making the molecules of water move
faster until it reaches its boiling point. When this happens, all of the molecules go further
apart and become a gas. The process of gas molecules leaving the liquid to go into the
gas is called "evaporation."
Water will become ice if its temperature reaches around 0°C, making the molecules
stick together and form a solid – ice.
Ice will melt if heat energy (melting point) from the warmer air is absorbed and
enough to break apart the particle arrangements of ice water allowing the molecules
to move faster, breaking the hydrogen bonds between molecules to form liquid water.
Water vapor will condense if the molecules in a gas cool down, losing the heat
energy and making the molecules slow down. As is slows down, the gas molecules move
closer to other gas molecules until these molecules collect together to form a liquid.
The next thing that we are concerned about is the phase diagram of water which
will then be compared to the phase diagram of carbon dioxide. But before that, let us
be familiar first with what is phase diagram.

Phase diagram

A phase diagram is a graph that

relates pressure and temperature to
the state of matter. These two
important intensive properties will help
us determine the phases of matter.
From the given figure 2 on the phase
diagram, we see the three sections
represented by the three phases of
matter (solid, liquid, and gas). Lines in
the graph are boundaries that signify
the dynamic equilibrium between two
or three phases.
How do changes of phase
happen? It is by either changing the
temperature or pressure. We have a
couple of interesting two points given
in the graph which are triple point and the critical point. Triple point is the point where
at a certain pressure and temperature at equilibrium all three phases of a substance co-
exist, meaning it is the same rate where solid becomes liquid or gas becomes liquid. On
 Suggested
IV. LEARNING PHASES Learning Activities
Timeframe
the other hand, a critical point corresponds to a specific pressure and temperature
above which the fluid has both properties of liquid and vapor. This would also mean that
liquid and gas are at the same density, which made them indistinguishable. And once
you go further the critical point, everything beyond this point is considered as
“supercritical fluid”. Critical temperature is where a substance is impossible to liquefy no
matter how you increase or compress the substance.
Study and analyze the phase diagrams of water (left) and carbon dioxide (right).

Heating Curve of Water

Like many substances, water exists in different phases of matter: liquid, solid, and gas.
As water is heated up at a constant rate, the temperature changes which is shown in
the heating curve of water. The heating curve of water or any substances can be drawn
by plotting the temperature on the y-axis, while the x-axis represents the heat that is
constantly added over time. There are two main observations on the measured curve;
one of which is the region where the temperature increases as heat is added and
plateaus where the temperature stays constant. What is the significance of plateaus on
the heating curve? It is at plateaus where a phase change occurs.
Let us analyze the
heating curve of
water by looking at
the graph from left to
the right. There are
five important parts
of the heating curve,
these are:
(1) The solid ice is
heated until the
temperature reaches
0°C where a freezing
point or melting point
is reached at point A.
(2) The melting
period happens in
segment A to B
where the
temperature is held
constant.
(3) The temperature of this liquid rises in segment B to C as the heat is absorbed by the
system.
(4) The temperature will become constant again in segment C to D at 100 °C which is
the boiling point of water.
(5) At point D, all liquid water has become gaseous water at 1 atm and 100°C.

References:
Chang, Raymond. 2010. Chemistry 10th edition. McGraw-Hill College.
 Suggested
IV. LEARNING PHASES Learning Activities
Timeframe
B. Development 40 mins Learning Task 1: Refer to the given phase diagram below to answer the following
Pagpapaunlad questions.
1. Which section
would be in:
a. solid phase: ____
b. liquid phase: ____
c. gas phase: ____

2. At 1 atm, what
would be the
substance`s:
a. boiling point: ____
b. melting point: ____
c. critical
temperature: ____
3. At triple point,
what would be the
substance`s:
a. temperature: ____
b. pressure: ____
4. What would you do to cause a substance to change from a solid phase to a liquid
phase at constant temperature? __________________________________
5. What would you expect to a substance melting to a liquid phase or subliming to a
gas at 1 atm and room temperature? __________________________________
C. Engagement 40 mins Learning Task 2: Use the heating curve of ethanol to answer the questions below.
Pakikipagpalihan

Questions:
1. What point where ethanol begins to melt? _________________________
2. What is ethanol`s melting point? ___________________
3. What point where ethanol is all done melting? __________________
4. Between what point where solid and liquid ethanol co-exist? ________________
5. At what point is ethanol is all in its gas phase? _______________
6. Between what point where liquid and gas ethanol co-exist? ________________
7. Between what point where heat of fusion exist? _________________
8. Between what point where heat of vaporization exist? _______________
D. Assimilation 30 mins Learning Task 3: Choose only one situation and answer the indicated question.
Paglalapat 1. In some industries, carbon dioxide is stored in large tanks. Assuming that we live at sea
level, suggest or mention ways to liquefy carbon dioxide that will not harm human
being?
2. Many may not be aware of a “NO FROST” refrigerator and some are aware of a
refrigerator where ice-cold built up in the fridge. Suggest ways to properly defrost a
freezer using hand. State your answer in a bullet form.
 Suggested
IV. LEARNING PHASES Learning Activities
Timeframe
V. ASSESSMENT 35 mins Choose the letter of the best answer and write your answer on a separate sheet of
(Learning Activity paper.
Sheets for 1. Which of the choices is defined as a point where supercritical fluid occurs?
Enrichment,
A. critical point
Remediation or
Assessment to be B. phaIe change
given on Weeks 3 C. phase diagram
and 6) D. triple point
2. What are the two intensive properties of matter that will help us determine the phases
of matter?
A. density and volume C. pressure and temperature
B. density and pressure D. temperature and volume
3. Which best describes the slope of the solid-liquid boundary of carbon dioxide?
A. a negative slope
B. a positive slope
C. cannot be determined because carbon dioxide is unstable
D. a positive slope because carbon dioxide shows an unstable property
4. At what temperature and pressure would show the triple point of carbon dioxide?
A. at 1 °C and 6 atm C. -57 °C and 5.11 atm
B. at 0.01 °C and 0.006 atm D. -57.2 °C and 5.2 atm
5. What does the line in the phase diagram represent?
A. boiling point and freezing point of a substance
B. melting point and boiling point of a substance
C. boundaries that signifies the dynamic equilibrium between two or three phases
D. these are boundaries that would show the sections in any phase diagrams
of substances
For items 6 to 10, refer to the given heating curve of naphthalene:
6. At what point in the heating
curve of naphthalene
represents the solid
naphthalene starts to melt?
A. A B. B C. C D. F
7. At what point from the given
heating curve of naphthalene
represents the liquid
naphthalene starts to boil?
A. B B. C C. D D. E
8. In which segment is the
kinetic energy remains
constant?
A. A-B B. B-C C. C-D D. E-F

9. Which segment takes the longest to occur?

A. A – B B. B – C C. C – D D. D – E
10. What state (s) of matter is present in segment B – C?
A. liquid B. solid C. solid and liquid D. liquid and gas
VI. REFLECTION 5 mins • The learner, in their notebook, will write their personal insights about the lesson using
the prompts below.
I understand that ___________________.
I realize that ________________________.
I need to learn more about __________.

Prepared by: Engr. Mary Rose D. Aguila Checked by: