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

A matéria normalmente existe no estado sólido, líquido ou gasoso. Nos gases, as moléculas de alta energia se movem rapidamente e estão distantes, de modo que as forças intermoleculares atrativas são fracas.
Mudanças de temperatura, pressão ou ambas podem desencadear transições de fase, ou mudanças de fase, entre os estados da matéria.
Durante essas transições, a energia flui de ou para o sistema sem uma mudança na temperatura.
A mudança de energia necessária para a transição completa de um mol de uma substância é a entalpia molar dessa transição.
Comprimir ou resfriar um gás torna mais difícil para as moléculas se afastarem umas das outras, transformando-as em um líquido mais denso e menos compressível.
O resfriamento do líquido reduz a energia cinética, transformando-a em um arranjo densamente compactado de um sólido incompressível.

estados da matéria e mudanças de fase

A energia interna de uma substância – a energia cinética total de todas as suas moléculas e a energia potencial das forças associadas – depende da intensidade das forças intermoleculares nas fases condensadas e da pressão exercida sobre a substância. A energia interna de uma substância é maior no estado gasoso, menor no estado sólido e intermediária no estado líquido. As transições de fase é causadas por mudanças nas condições físicas, como temperatura e pressão, que afetam as interações intermoleculares. Por exemplo, a adição de calor a uma substância faz com que a energia térmica das suas partículas aumente. Quando o calor total adicionado faz com que as partículas de um sólido vibrem com rapidez suficiente para superar a atração intermolecular, elas saem de suas posições fixas. Essa transição de fase é chamada de fusão, e o ponto em que ocorre é o ponto de fusão do sólido. À medida que a temperatura aumenta ainda mais, as partículas movem-se mais rapidamente até finalmente escaparem para o estado gasoso. Isto é vaporização, e o ponto em que ocorre é o ponto de ebulição do líquido. Durante uma transição de fase, as moléculas existem em ambas as fases simultaneamente e a temperatura da substância permanece constante apesar do fluxo contínuo de calor. Após a conclusão da transição da maior parte da substância, a temperatura da substância aumenta.

O ponto de transição de fase e a mudança de energia associada à transição dependem das forças intermoleculares que existem na substância. A uma determinada pressão, as substâncias com forças intermoleculares mais fortes requerem mais energia para sofrerem transições de fase, então estas transições ocorrem a temperaturas mais elevadas do que as substâncias com interações intermoleculares mais fracas. A energia necessária para causar a transição de fase completa de um mol de uma substância, sem mudança de temperatura, é chamada de calor molar ou entalpia molar dessa transição. Por exemplo, a energia necessária para vaporizar um mol de um líquido é chamada de entalpia molar de vaporização. As reações ou transições que absorvem energia é endotérmicas e as reações ou transições que liberam energia é exotérmicas. As reações que absorvem energia têm valores de entalpia positivos, enquanto as reações que liberam energia têm valores de entalpia negativos. Por exemplo, embora a entalpia molar de vaporização seja positiva, a entalpia molar de condensação é negativa, portanto a vaporização é um processo endotérmico enquanto a condensação é exotérmica.

Estados da Matéria e Mudanças de Fase

A energia interna de uma substância - a energia cinética total de todas as suas moléculas e a energia potencial de suas forças associadas - depende ...

Education

JoVE Core

Analytical Chemistry

Química Analítica

Unit 1

Unidade 1

Introduction to Separation Methods

Introdução aos Métodos de Separação

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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

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Classifying Matter by Composition

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Physical Properties of Matter

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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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Surface Tension, Capillary Action, and Viscosity

Surface Tension
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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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Heating and Cooling Curves

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Phase Diagrams

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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

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

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Internal Energy

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Quantifying Heat

Thermal Energy&#160;

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Quantifying Work

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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

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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

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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

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Standard Enthalpy of Formation

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Enthalpies of Reaction

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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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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

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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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PS.Chm.7.3

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

Heating and Cooling During Phase Changes

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