Name: phase changes on heating and cooling curves
Uploaded: 2020-09-24T15:06:49.000Z
Duration: 2 min 44 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Chemistry

Energy

PS.Chm.7.1

Heating and Cooling Curves

Heating or cooling a substance leads to temperature changes, followed by phase changes. 
Heating a substance increases its molecules&#39; thermal energy, which is reflected as a rise in temperature until it reaches a transition point.
When the substance has absorbed enough heat, the attractive forces between its molecules are overcome, leading to a phase transition at a constant temperature. 
Once the transition is complete, heating results in a rise in temperature again.
When heat is removed from the substance, the decrease in its molecules&#8217; thermal energy corresponds to a drop in temperature, until it reaches a transition point.
Then, the temperature remains constant as stronger intermolecular forces are re-established during the phase change.
The behavior of a substance in response to temperature changes can be modeled using heating curves or cooling curves, where the temperature change is plotted as a function of the heat added or heat removed.
Consider a beaker filled with ice cubes, initially at &#8722;20 &#176;C. As heat flows in, the temperature of the ice rises steadily. The amount of heat absorbed in warming the ice depends on the specific heat capacity of ice.
Once the melting point of i

heating and cooling curves

When a substance&#8212;isolated from its environment&#8212;is subjected to heat changes, corresponding changes in temperature and phase of the substance is observed; this is graphically represented by heating and cooling curves.
For instance, the addition of heat raises the temperature of a solid; the amount of heat absorbed depends on the heat capacity of the solid (q = mcsolid&#916;T). According to thermochemistry, the relation between the amount of heat absorbed or released by a substance, q, and its accompanying temperature change, &#916;T, is:
<img alt="Quantum harmonic oscillator, energy level symbols, physics equation diagram, eigenvalues depiction" src="/files/ftp_upload/11351/11351_Equation_1.png" style="text-align: center; height: 50px;" data-altupdatedat="1754904545000" data-alt="First-order logic diagram with formulas, showing logical relationships and quantifiers." />
where m is the mass of the substance, and c is its specific heat. The relation applies to matter being heated or cooled, but not changing state.
When the temperature is high enough, the solid begins to melt (Figure 1, point A). The heat absorbed depends on the solid&#8217;s heat capacity (q = mcsolid&#916;T), and a plateau is observed at its melting point. The plateau indicates a change of state from solid to liquid, during which the temperature does not rise due to the heat of fusion (q = m&#916;Hfusion). In other words, further heat gain is a result of diminishing intermolecular attractions, instead of increasing molecular kinetic energies. Consequently, while a substance is changing state, its temperature remains constant.
Once the solid has completely melted (Figure 1, point B), the liquid starts warming and experiences a rise in temperature. The heat absorbed depends on the liquid's heat capacity (q = mcliquid&#916;T). When the liquid reaches its boiling point, the liquid begins to vaporize (Figure 1, point C) and the temperature remains constant despite the continued input of heat. Another plateau (constant temperature) is observed at the liquid's boiling point during the liquid to gas transition due to the heat of vaporization (q = m&#916;Hvap). This same temperature is maintained by the liquid as long as it is boiling. If heat is provided at a greater rate, the liquid's temperature does not rise, but instead, the boiling becomes more vigorous (rapid). After all the liquid has vaporized (Figure 1, point D), the temperature of the gas increases.
<img alt="Heating curve diagram, phases changes of water with equations q=mc&#916;T, n&#916;H, transition states." src="/files/ftp_upload/11351/11351_Image_1.png" style="text-align: center; height: 330px;" data-altupdatedat="1754904545000" data-alt="Phase change process, heating curve diagram with q=mc&#916;T, n&#916;H equations shows heat transfer stages." />
Figure 1. The representative heating curve for a substance depicts changes in temperature that result as the substance absorbs increasing amounts of heat. Plateaus in the curve (regions of constant temperature) are exhibited when the substance undergoes phase transitions.
This text is adapted from <a href="https://openstax.org/books/chemistry-2e/pages/10-3-phase-transitions">Openstax, Chemistry 2e, Section 10.3: Phase Transitions</a>.

When a substance&#8212;isolated from its environment&#8212;is subjected to heat changes, corresponding changes in temperature and phase of the substance ...

Education

JoVE Core

Liquids, Solids, and Intermolecular Forces

KEY TERMS AND CONCEPTS

phase changes on heating and cooling curves

Phase changes on heating and cooling curves show how a substance responds when it absorbs or releases heat while isolated from its surroundings. The graph tracks changes in temperature and state as the substance is heated or cooled.

When a solid is heated, its temperature rises first. The amount of heat absorbed depends on the solid’s heat capacity, which is written as q = mcΔT. In this equation, m is the mass and c is the specific heat. This relationship applies when matter changes temperature without changing state.

As the solid reaches its melting point, it begins to melt. The graph levels off at a plateau, or flat section. During this change from solid to liquid, the temperature stays constant because the heat added becomes heat of fusion, written as q = mΔHfusion. The added energy weakens intermolecular attractions instead of increasing molecular kinetic energy.

After the solid has fully melted, the liquid warms again and its temperature rises. The heat absorbed now depends on the liquid’s heat capacity, so the same q = mcΔT relationship applies. When the liquid reaches its boiling point, it begins to vaporize and another plateau appears. The temperature stays constant during this liquid-to-gas change because the heat added becomes heat of vaporization, written as q = mΔHvap.

The substance remains at the boiling temperature as long as it is boiling. If heat is added faster, the temperature still does not rise. Instead, the boiling becomes more vigorous. Once all of the liquid has turned to gas, the gas temperature increases again.

Phase Changes on Heating and Cooling Curves

phase-changes-on-heating-and-cooling-curves

molecular comparison of gases, liquids, and solids

molecular-comparison-of-gases-liquids-and-solids

How Intermolecular Forces Shape States

Intermolecular forces and particle motion shape the states of matter: solids, liquids, and gases. In a solid, particles are tightly packed and often arranged in a regular pattern. A solid has a fixed shape, and its particles vibrate in place rather than flowing past one another. In a liquid, particles stay close together but do not have a regular arrangement. Liquids have no fixed shape, yet their particles move past each other while remaining in contact. That is why liquids can flow and take...

intermolecular vs intramolecular forces

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intermolecular forces

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comparing intermolecular forces: melting point, boiling point, and miscibility

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How Molecule Shape Affects Intermolecular Forces

Intermolecular forces are the attractions between molecules, and they help explain melting point, boiling point, and miscibility. Their strength depends on molar mass, molecular shape, and polarity. These forces shape the bulk behavior of substances that students see in chemistry labs. Dispersion forces are temporary attractions that occur in every substance, whether it is polar or nonpolar. They form when electrons are spread unevenly for a moment, creating a temporary dipole. Stronger...

surface tension, capillary action, and viscosity

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phase transitions

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phase transitions: vaporization and condensation

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Heat and Mass Transfer in Phase Changes

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vapor pressure

Vapor Pressure and Boiling Point

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clausius-clapeyron equation

Predicting Vapor Pressure with Temperature

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phase transitions: melting and freezing

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phase transitions: sublimation and deposition

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Sublimation, Frost, and Enthalpy Changes

Sublimation is a phase change in which a solid turns directly into a gas. It skips the liquid state. Dry ice is a clear example at room temperature and standard pressure, where solid carbon dioxide seems to disappear as it sublimes without forming a liquid first. Some other solids also sublime under the right conditions. Snow and ice can sublimate below water’s melting point, and wind or the lower air pressure at high altitudes can speed up that slow process. Solid iodine does the same when...

Phase changes on heating and cooling curves show how a substance responds when it absorbs or releases heat while isolated from its surroundings. The graph tracks changes in temperature and state as the substance is heated or cooled. When a solid is heated, its temperature rises first. The amount of heat absorbed depends on the solid’s heat capacity, which is written as q = mcΔT. In this equation, m is the mass and c is the specific heat. This relationship applies when matter changes...

phase diagrams

Water and CO2 Phase Behavior

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structures of solids

Crystalline and Amorphous Solid Patterns

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solids

Molecular and Ionic Crystal Properties

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metallic solids

Metallic Bonding and Crystal Packing

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band theory

Band Gaps in Conductors and Insulators

Band gaps in solids help explain why some materials conduct electricity and others do not. When many atoms come together, their atomic orbitals combine into molecular orbitals with distinct energies. In a solid, so many orbitals are involved that these energies merge into continuous regions called bands. The energy difference between bands is called the band gap. Electrons in a solid must move across orbitals of different energies to travel through the material. In conductors, the valence...

network covalent solids

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Network covalent solids are made of atoms joined in a three-dimensional network of covalent bonds. They appear in the crystal structures of nonmetals such as diamond, graphite, and silicon. Some covalent compounds also form this kind of structure, including silicon dioxide, which is found in sand, and silicon carbide, the abrasive used on sandpaper. Many minerals also contain networks of covalent bonds. These solids are hard to melt or break because their covalent bonds must be broken first.

x-ray crystallography

X-ray Diffraction in Crystal Structure

X-ray diffraction can reveal the unit cell size and atom arrangement in a crystal. This method is called X-ray crystallography. It uses diffraction, which is the bending of an electromagnetic wave when it meets a barrier about the same size as its wavelength. X-rays work well for this method because their wavelengths are about the same as the spacing between neighboring atoms in crystals. They are measured on the scale of a few angstroms. When monochromatic X-rays, or X-rays with one...

lattice centering and coordination number

lattice-centering-and-coordination-number

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key terms and concepts

See how heating and cooling curves show melting, boiling, and temperature plateaus as a substance absorbs heat and changes state.

Phase Changes on Heating and Cooling Curves | JoVE K12

chemistry

JoVE Core Chemistry brings general chemistry concepts to life using concise and easy-to-understand animated video lessons. Plus, in the scientist-in-action videos, we demonstrate classical and original research experiments performed in today's laboratories worldwide.

Physical Science

Matter and its Interactions

PS.PSc.1.2

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Study Of Matter

Classification of matter

Energy And Waves

Thermal energy

Structure And Properties Of Matter

Intermolecular forces of attraction

Tennessee Academic Standards

High School

CHEM1.PS3.2

Virginia  Standards of Learning

HIgh School

CH.6

CH.6.a

CH.7

CH.7.b

PS.3

PS.3.b

Arizona Science Standards

HS+Phy.P4

HS+Phy.P4U1.6

Texas Essential Knowledge and Skills

CHEM.11

CHEM.11.C

Alabama Course of Study Science

Matter and Its Interactions

9-12.C.1.5.d

9-12.PS.3.5.b

Florida Department of Education

SC.912.P.8

SC.912.P.8.2

SC.912.P.12

SC.912.P.12.11

Georgia Standards of Excellence

SPS5.

Energy and Phase Transitions

SPS7.

Heating/Cooling Curves

SC5.

Heating Curves and Phase Changes

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Surface Tension, Capillary Action, and Viscosity

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Phase Transitions

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Phase Transitions: Vaporization and Condensation

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Vapor Pressure

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Clausius-Clapeyron Equation

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Phase Transitions: Melting and Freezing

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Phase Transitions: Sublimation and Deposition

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Use models to explain how changes in energy affect the arrangement and movement of the particles in solids, liquids, and gases, as well as the relative strengths of their intermolecular forces.

Energy Basics

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First Law of Thermodynamics

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Internal Energy

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Quantifying Heat

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Standard Enthalpy of Formation

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PS.Chm.7.2

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PS.Chm.7.3

Understand the relationship among pressure, temperature, volume, and phase.

Phase Changes on Heating and Cooling Curves

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