Name: heating and cooling during phase changes
Uploaded: 2024-04-04T10:51:23.000Z
Duration: 59 s
Channel: JoVE

K12 Standards

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

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Energy

PS.Chm.7.1

States of Matter and Phase Changes

Materie liegt typischerweise im festen, flüssigen oder gasförmigen Zustand vor. In Gasen bewegen sich die hochenergetischen Moleküle schnell und sind weit voneinander entfernt, so dass die anziehenden intermolekularen Anziehungskräfte schwach sind.
Änderungen der Temperatur, des Drucks oder beider können Phasenübergänge oder Phasenänderungen zwischen Aggregatzuständen auslösen.
Während dieser Übergänge fließt Energie ohne Temperaturänderung in das oder aus dem System.
Die Energieänderung, die für den vollständigen Übergang eines Mols einer Substanz erforderlich ist, ist die molare Enthalpie dieses Übergangs.
Das Komprimieren oder Abkühlen eines Gases erschwert es den Molekülen, sich voneinander zu entfernen, wodurch sie in eine dichtere, weniger komprimierbare Flüssigkeit umgewandelt werden.
Durch das Abkühlen der Flüssigkeit wird die kinetische Energie reduziert und sie in eine dicht gepackte Anordnung eines inkompressiblen Festkörpers umgewandelt.

aggregatzustände und phasenänderungen

Die innere Energie einer Substanz – die gesamte kinetische Energie aller ihrer Moleküle und die potentielle Energie der damit verbundenen Kräfte – hängt von der Stärke der intermolekularen Kräfte in den kondensierten Phasen und dem auf die Substanz ausgeübten Druck ab. Die innere Energie eines Substanz ist im gasförmigen Zustand am höchsten, im festen Zustand am niedrigsten und im flüssigen Zustand auf einem mittleren Niveau. Phasenübergänge werden durch Änderungen physikalischer Bedingungen wie Temperatur und Druck verursacht, die sich auf intermolekulare Wechselwirkungen auswirken. Wird einer Substanz beispielsweise Wärme zugeführt, erhöht sich die Wärmeenergie ihrer Teilchen. Wenn die insgesamt zugeführte Wärme dazu führt, dass die Partikel in einem Festkörper schnell genug vibrieren, um ihre intermolekulare Anziehungskraft zu überwinden, bewegen sie sich aus ihrer festen Position. Dieser Phasenübergang wird Schmelzen genannt und der Punkt, an dem er auftritt, ist der Schmelzpunkt des FestSubstanzs. Mit zunehmender Temperatur bewegen sich die Partikel schneller, bis sie schließlich in den gasförmigen Zustand entweichen. Dies ist die Verdampfung, und der Punkt, an dem sie auftritt, ist der Siedepunkt der Flüssigkeit. Bei einem Phasenübergang existieren Moleküle gleichzeitig in beiden Phasen und die Temperatur des Substanz bleibt trotz der kontinuierlichen Wärmezufuhr konstant. Nachdem der Übergang der Masse des Substanz abgeschlossen ist, steigt die Temperatur des Substanz.

Der Phasenübergangspunkt und die mit dem Übergang verbundene Energieänderung hängen von den in der Substanz vorhandenen intermolekularen Kräften ab. Bei einem bestimmten Druck benötigen Substanzen mit stärkeren zwischenmolekularen Kräften mehr Energie, um einen Phasenübergang zu vollziehen, so dass diese Übergänge bei höheren Temperaturen stattfinden als bei Substanzenn mit schwächeren zwischenmolekularen Wechselwirkungen. Die Energie, die erforderlich ist, um den vollständigen Phasenübergang eines Mols einer Substanz ohne Temperaturänderung herbeizuführen, wird als molare Wärme oder molare Enthalpie dieses Übergangs bezeichnet. So wird beispielsweise die Energie, die erforderlich ist, um ein Mol einer Flüssigkeit zu verdampfen, als molare Verdampfungsenthalpie bezeichnet. Reaktionen oder Übergänge, die Energie absorbieren, sind endotherm, und Reaktionen oder Übergänge, die Energie freisetzen, sind exotherm. Reaktionen, die Energie absorbieren, haben positive Enthalpiewerte, während Reaktionen, die Energie freisetzen, negative Enthalpiewerte haben. Während beispielsweise die molare Verdampfungsenthalpie positiv ist, ist die molare Kondensationsenthalpie negativ, sodass die Verdampfung ein endothermer Prozess ist, während die Kondensation exotherm ist.

Aggregatzustände und Phasenänderungen

Die innere Energie einer Substanz – die gesamte kinetische Energie aller ihrer Moleküle und die potentielle Energie der damit verbundenen Kräfte – hängt von ...

Education

Lehre

JoVE Core

Analytical Chemistry

Analytische Chemie

Unit 1

Einheit 1

Introduction to Separation Methods

Einführung in Trennmethoden

KEY TERMS AND CONCEPTS

SCHLÜSSELBEGRIFFE UND KONZEPTE

heating and cooling during phase changes

Heating and cooling can change a substance from one state of matter to another. These phase changes depend on internal energy, which is the total kinetic energy of particles and the potential energy from their interactions. In the condensed phases, stronger intermolecular forces and the pressure on the substance affect that internal energy. The internal energy is highest in the gaseous state, lowest in the solid state, and in between for the liquid state.

Phase transitions happen when temperature or pressure changes alter intermolecular interactions. When heat is added, the thermal energy of the particles increases. In a solid, the particles can vibrate fast enough to overcome their attraction and leave fixed positions. This change is melting, and the temperature where it happens is the melting point.

If heating continues, the particles move faster and eventually escape into the gaseous state. This change is vaporization, and the temperature where it happens is the boiling point of the liquid. During a phase transition, molecules are present in both phases at the same time. The temperature stays constant even though heat keeps being added. After the bulk of the substance finishes changing phase, the temperature rises again.

The temperature of a phase change depends on the intermolecular forces in the substance. At the same pressure, substances with stronger intermolecular forces need more energy to change phase. As a result, they change at higher temperatures than substances with weaker intermolecular attractions. The energy needed to change one mole of a substance completely without changing temperature is called the molar heat, or molar enthalpy, of the transition.

For vaporization, this energy is the molar enthalpy of vaporization. It is positive because vaporization absorbs energy, so it is an endothermic process. Condensation has the opposite sign. It releases energy, so it is exothermic and has a negative enthalpy value.

Heating and Cooling During Phase Changes

states of matter and phase changes

Heating and cooling can change a substance from one state of matter to another. These phase changes depend on internal energy, which is the total kinetic energy of particles and the potential energy from their interactions. In the condensed phases, stronger intermolecular forces and the pressure on the substance affect that internal energy. The internal energy is highest in the gaseous state, lowest in the solid state, and in between for the liquid state. Phase transitions happen when...

distillation: vapor&ndash;liquid equilibria

Distillation and Boiling Point Changes

Distillation separates a miscible liquid mixture by using differences in boiling points. It works best when the two liquids have a significant boiling point gap, usually at least 20°C. In this process, the mixture is heated until the more volatile component reaches its bubble point and begins to vaporize. The vapor then rises into a condenser. A condenser is a glass tube with separate inner and outer sections. Cold water flows through the outer section and cools the vapor in the inner section,...

filtration

Filtration Setup and Filtrate Collection

Filtration separates a solid from a liquid by passing a suspension through a porous medium. The solid stays on the filter, and the liquid, called the filtrate, passes through. This makes filtration a physical separation process, not a chemical change. The filtering medium is chosen for the purpose of the separation, the amount of material, and the nature of the precipitate. A good filter medium should be inert, mechanically strong, nonabsorbent toward dissolved materials, and able to let...

centrifugation

Centrifugation for Separating Particles

Centrifugation separates particles in a liquid by using differences in size and density. The sample is placed in centrifugation tubes and spun at high angular velocity. This creates centrifugal force, which makes the different components move at different rates. After spinning, the supernatant, or liquid above the settled material, is decanted. In some cases, the pellet is kept for further purification. In other cases, the supernatant is kept and may be spun again for additional processing. <br...

sublimation

Sublimation in Separation and Purification

Sublimation is the direct change of a solid into a gas. It skips the liquid state. A common example is solid carbon dioxide, or dry ice, which turns into gaseous carbon dioxide at standard pressure and room temperature. The phase diagram shows when sublimation can happen. This process occurs at the solid-gas boundary. It is not seen above the triple point of a substance. The reverse process is deposition, which is when a gas changes directly into a solid. Sublimation and deposition can help...

recrystallization: solid&ndash;solution equilibria

recrystallization-solidsolution-equilibria

Recrystallization for Purifying Solid Compounds

Recrystallization is a way to purify solid compounds by using differences in solubility. It does not involve a chemical reaction. Instead, it relies on physical properties of the desired compound and the impurities. The process is based on solid-solution equilibrium, also called solubility equilibrium. In this equilibrium, a component is split between the solid phase and the solution phase. At equilibrium, the chemical potential of that component is the same in both phases. To begin...

crystal growth: principles of crystallization

crystal-growth-principles-of-crystallization

Crystal Formation Through Supersaturation

Crystal formation through supersaturation begins when a solution contains more dissolved solute than it can normally hold. In crystallization, atoms or molecules line up into a rigid crystal lattice so the system can lower its energy. To start the process, the solute concentration and the solution temperature must be adjusted so the supersaturation ratio, S, is greater than one. Supersaturation can be increased in two main ways. One method is to concentrate the solution by evaporating the...

precipitation and co-precipitation

Selective Ion Separation by Precipitation

Selective ion separation by precipitation is used to isolate ions from a solution. In qualitative inorganic analysis, ions that form sparingly soluble precipitates with the same reagent can be separated by using differences in their solubility products. A solubility product is the limit at which an ionic solid begins to form from dissolved ions. One example is the separation of Cu(II) and Fe(II) ions as insoluble sulfides. Copper(II) sulfide is first precipitated by adding acidic H2S. The acid...

coagulation

Wastewater Cleanup by Coagulation

Coagulation helps remove colloidal particles from wastewater. Colloids are tiny solid particles suspended in a liquid. They are usually negatively charged, so they attract a compact first layer of positive ions. More counterions gather around them and form an electrical double layer. This charge barrier keeps the particles apart and stabilizes the colloid. These suspended solids can be a problem because they may contain toxins that are hard to remove. Coagulation is used to make the particles...

electrodeposition

Electrodeposition for Metal Ion Separation

Electrodeposition separates metal ions from a solution by using an electric current and an electrolytic cell. The cell has an anode and a cathode. When current flows, oxidation happens at the anode. At the cathode, metal ions gain electrons, undergo reduction, and deposit on the large metal surface. This method works well when metals have very different reduction potentials. Copper and nickel in the same solution can be separated this way. First, the solution is made acidic. Then current is...

extraction: partition and distribution coefficients

extraction-partition-and-distribution-coefficients

Solvent Partitioning in Chemical Extraction

Solvent partitioning in chemical extraction describes how a solute spreads between two immiscible solvents. Immiscible solvents do not mix, such as an aqueous phase and an organic phase. The distribution law, also called Nernst's distribution law or the partition law, explains how that solute is shared at a constant temperature and equilibrium. At equilibrium, the ratio of solute concentrations in the two solvents stays constant. For extraction from water into an organic solvent, this...

extraction: effects of ph

pH Control in Liquid Extraction

pH control in liquid extraction changes how amines and acids move between organic and aqueous phases. The pH of the aqueous phase affects the charge on acidic and basic solutes. The charged form is usually more soluble in the aqueous phase. For a weak base such as an amine, the neutral form is called B. Its partition coefficient, K, describes how the neutral molecule distributes between the two liquids. If the conjugate acid of the amine is soluble only in the aqueous phase, while the base...

extraction: advanced methods

Chelate Extraction for Metal Ion Separation

Chelate extraction is a way to separate metal ions by using an organic ligand, or chelating agent, to form an uncharged metal complex. The chelating agent needs hydrophobic groups, and it must act as a weak acid so it can lose a proton and bind to the metal. Most organic ligands used for this method are not stable in water or are insoluble in the aqueous phase. For that reason, the chelating agent is first placed in the organic phase. It then moves into the aqueous phase, where the...

chromatography: introduction

Chromatography: Separation by Polarity

Chromatography separates compounds by how they divide between a stationary phase and a mobile phase. The stationary phase is the material that holds the compounds for a time. The mobile phase is the solvent that carries the solutes to be analyzed. In column chromatography, a mixture flows through the stationary phase. The compounds separate based on their structure and polarity. Solutes that interact weakly with the stationary phase move faster through the column and exit first. Solutes that...

dialysis

Dialysis Separation by Diffusion

Dialysis separates small molecules from larger ones by diffusion through a semipermeable membrane. It is a purification method used to remove unwanted ions or small organic molecules from a sample while keeping larger analytes in place. The membrane is usually made of cellulose acetate or cellulose nitrate. Its pores are typically about 1 to 5 nm wide. Molecules such as chloride, sodium, and glucose can pass through these pores. Larger molecules, including proteins, hormones, and enzymes, are...

volatilization

Mass Loss in Gravimetric Analysis

Volatilization gravimetry is a way to measure mass loss in a sample by driving off a volatile substance. It helps estimate how much volatile material is present. In this method, a known amount of sample is heated to a high temperature in a crucible or another suitable vessel. As the sample heats, the volatile substance evaporates. The vapor is then completely removed from the crucible, either by continued heating or by bubbling an inert gas through the vessel. The non-volatile part stays...

ion exchange

Ion Exchange Resins and Charged Molecules

Ion exchange chromatography separates charged molecules from a solution by swapping them with mobile, or active, ions on a stationary phase. It is used to separate ions, soften and deionize water, and purify solutions. The method depends on a solid column made of high-molecular-weight, chemically stable polymers that are crosslinked to make them porous and essentially insoluble. These polymers are functionalized with either acidic or basic groups. When acidic groups are present, the resin is a...

key terms and concepts

Learn how heat changes matter from solid to liquid to gas, why temperature stays constant during phase changes, and how melting, boiling, and condensation differ.

Heating and Cooling During Phase Changes | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Louisiana Student Standards for Science

High School

Matter And Its Interactions

HS-PS1-4

HS-PS1-5

Tennessee Academic Standards

Matter and Its Interactions

CHEM1.PS1.7

Alabama Course of Study Science

Earth and Space Science

Earth's Systems

9-12.ESS.2.7

9-12.ESS.2.7.a

Florida Department of Education

Physical Science

SC.912.P.8

SC.912.P.8.1

Georgia Standards of Excellence

SPS5.

Energy and Phase Transitions

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

physical-and-chemical-properties-of-matter

Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

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Molecular Comparison of Gases, Liquids, and Solids

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Intermolecular vs Intramolecular Forces

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Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions ...

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Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility

Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, ...

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Surface Tension, Capillary Action, and Viscosity

Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded ...

The internal energy of a substance&#8212;the total kinetic energy of all its molecules and the potential energy of their associated forces&#8212;depends ...

Phase Transitions

Whether solid, liquid, or gas, a substance&#39;s state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the ...

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Phase Transitions: Vaporization and Condensation

The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

Vapor Pressure

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Clausius-Clapeyron Equation

The equilibrium between a liquid and its vapor depends on the temperature of the system; a rise in temperature causes a corresponding rise in the vapor ...

Phase Transitions: Melting and Freezing

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phase-transitions-sublimation-and-deposition

Phase Transitions: Sublimation and Deposition

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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 ...

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

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

Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter.

Chemical changes and their accompanying ...

First Law of Thermodynamics

Energy Conservation

Energy can be converted from one form into another, but all of the energy present before a change occurs always exists in some form ...

Internal Energy

The total of all possible kinds of energy present in a substance is called the internal energy (U), sometimes symbolized as E. Suppose a system with ...

Quantifying Heat

Thermal Energy&#160;

Microscopically, thermal energy is the kinetic energy associated with the random motion of atoms and molecules. Temperature is a ...

Quantifying Work

As a system undergoes a change, its internal energy can change, and energy can be transferred from the system to the surroundings, or from the ...

Enthalpy

Chemists ordinarily use a property known as enthalpy (H) to describe the thermodynamics of chemical and physical processes. Enthalpy is defined as the sum ...

Thermochemical Equations

For a chemical reaction (the system) carried out at constant pressure &ndash; with the only work done caused by expansion or contraction &ndash; the ...

Constant Pressure Calorimetry

Calorimetry is a technique used to measure the amount of heat involved in a chemical or physical process or to measure the heat transferred to or from a ...

Constant Volume Calorimetry

Calorimeters are useful to determine the heat released or absorbed by a chemical reaction. Coffee cup calorimeters are designed to operate at constant ...

using-differential-scanning-calorimetry-to-measure-changes-in-enthalpy

Using Differential Scanning Calorimetry to Measure Changes in Enthalpy

Source: Laboratory of Dr. Terry Tritt &#8212; Clemson University
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Hess's Law

There are two ways to determine the amount of heat involved in a chemical change: measure it experimentally, or calculate it from other experimentally ...

Standard Enthalpy of Formation

Enthalpy changes are typically tabulated for reactions in which both the reactants and products are at the same conditions. A standard state is a commonly ...

Enthalpies of Reaction

Hess&rsquo;s law can be used to determine the enthalpy change of any reaction if the corresponding enthalpies of formation of the reactants and products ...

Use mathematics and computational thinking to execute simple calorimetric calculations based on the Law of Conservation of Energy.

PS.Chm.7.2

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Definition and Measurement of Pressure: Atmospheric Pressure, Barometer, and Manometer

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Gas Laws: Boyle's, Gay-Lussac, Charles', Avogadro's, and Ideal Gas Law

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Applications of the Ideal Gas Law: Molar Mass, Density, and Volume

The volume occupied by one mole of a substance is its molar volume. The ideal gas law, PV = nRT, &nbsp;suggests that the volume of a given quantity of gas ...

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Mixtures of Gases: Dalton's Law of Partial Pressures and Mole Fractions

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Chemical Stoichiometry and Gases: Using Ideal Gas Law to Determine Moles

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Basic Postulates of Kinetic Molecular Theory: Particle Size, Energy, and Collision

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Kinetic Molecular Theory and Gas Laws Explain Properties of Gas Molecules

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Kinetic Molecular Theory: Molecular Velocities, Temperature, and Kinetic Energy

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Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

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Use mathematics and computational thinking to explain the relationships among pressure, temperature, volume, and quantity of gas, both qualitatively and quantitatively.

PS.Chm.7.3

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

Heating and Cooling During Phase Changes

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