Name: energy conservation and internal energy
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 2 min 16 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.7.2

First Law of Thermodynamics

Quando la benzina alimenta il motore di un'auto, l'energia prodotta viene rilasciata sotto forma di calore e lavoro. Nel motore a combustione di un'auto, la miscela di carburante e aria contiene energia chimica, che è un tipo di energia potenziale. Questa energia potenziale viene poi trasformata in energia cinetica attraverso una reazione di combustione che genera calore.

Il calore proveniente dalla reazione viene quindi convertito in lavoro dai gas caldi in espansione che spingono sul pistone, che poi fa girare l'albero motore, portando infine in moto l'auto. Tutte queste interconversioni energetiche devono seguire la prima legge della termodinamica:l'energia è sempre conservata e non può essere creata o distrutta. Per studiare i cambiamenti energetici in un sistema devono essere considerate tutte le fonti di energia, inclusa l'energia potenziale e cinetica.

L'energia totale all'interno di un sistema in un dato momento è chiamata energia interna, che ha il simbolo U maiuscola, o a volte simbolizzata con una E maiuscola. L'energia interna di un sistema può cambiare. L'energia interna di un'auto con il serbatoio pieno, il suo stato iniziale, è diversa dall'energia totale mentre l'auto è in funzione, ed è di nuovamente diversa quando il serbatoio è vuoto-il suo stato finale.

Se tutto il carburante viene utilizzato per guidare 300 o 50 miglia è irrilevante, quando il serbatoio è vuoto l'auto raggiunge un nuovo stato interno. Pertanto, l'energia interna è descritta come una funzione di stato, che non è influenzata da come il sistema è arrivato al suo stato attuale. Pertanto, la variazione dell'energia interna di un sistema, delta U, viene misurata come differenza fra i valori dei suoi stati finale e iniziale.

Poiché l'energia è conservata, il cambiamento nell'energia interna di un sistema deve essere accompagnato da un cambiamento uguale e opposto nell'energia dell'ambiente circostante. Nei sistemi chimici, la variazione di energia interna è descritta dalla differenza fra lo stato iniziale del reagente e lo stato finale del prodotto. Viene utilizzata per comprendere il flusso di energia di un sistema.ante.

Il sistema può essere chiuso, dove viene scambiata solo energia, oppure il sistema può essere isolato, dove non vengono scambiate né massa né energia.

prima legge della termodinamica

Conservazione dell'energia

L'energia essere convertita da una forma all'altra, ma tutta l'energia presente prima che avvenga un cambiamento esiste sempre in qualche forma dopo che il cambiamento stato completato. Questa osservazione espressa nella legge di conservazione dell'energia: durante un cambiamento chimico o fisico, l'energia non essere n creata n distrutta, sebbene possa cambiare forma.

Secondo la legge di conservazione della materia, non vi alcun cambiamento rilevabile nella quantit totale di materia durante un cambiamento chimico. Quando si verificano reazioni chimiche, i cambiamenti di energia sono relativamente modesti e i cambiamenti di massa sono troppo piccoli per essere misurati. Quindi valgono le leggi di conservazione della materia e dell’energia. Tuttavia, nelle reazioni nucleari, i cambiamenti di energia sono molto pi grandi (per fattori di un milione circa), i cambiamenti di massa sono misurabili e le conversioni di materia-energia sono significative.

Trasferimento di energia ed energia interna

Le sostanze agiscono come serbatoi di energia, il che significa che l'energia essere aggiunta o rimossa da esse. L'energia viene immagazzinata in una sostanza quando l'energia cinetica dei suoi atomi o molecole aumenta. La maggiore energia cinetica presentarsi sotto forma di maggiori traslazioni (viaggi o movimenti rettilinei), vibrazioni o rotazioni degli atomi o delle molecole. Quando l'energia termica viene persa, l'intensit di questi movimenti diminuisce e anche l'energia cinetica.

L'totalit di tutti i possibili tipi di energia presenti in una sostanza chiamata energia interna (U), talvolta simboleggiata come E.

Quando un sistema subisce un cambiamento, la sua energia interna cambiare e l’energia essere trasferita dal sistema all’ambiente circostante o dall’ambiente circostante al sistema. Pertanto, anche l'ambiente circostante sperimenta un cambiamento uguale e opposto nella sua energia.

L'energia interna un esempio di funzione di stato (o variabile di stato), mentre il calore e il lavoro non sono funzioni di stato. Il valore di una funzione di stato dipende solo dallo stato in cui si trova un sistema e non da come tale stato viene raggiunto. Se una quantit non una funzione di stato, il suo valore dipende da come viene raggiunto lo stato. Un esempio di funzione di stato l'altitudine o l'elevazione. Trovandosi sulla vetta del Monte Kilimangiaro a un'altitudine di 5895 m, non importa come sia stato raggiunto, se qualcuno abbia camminato l o vi si sia paracadutato. La distanza percorsa fino alla cima del Kilimangiaro, tuttavia, non una funzione statale. Si potrebbe salire alla vetta per un percorso diretto o per un percorso pi tortuoso. Pertanto, le distanze percorse sarebbero diverse (la distanza non una funzione di stato); tuttavia, l'altitudine raggiunta sarebbe la stessa (l'altitudine una funzione di stato).

Questo testo adattato da <a href="https://openstax.org/books/chemistry-2e/pages/5-1-energy-basics">OpenStax Chemistry 2e, Section 5.1: Energy Basics</a> and <a href="https://openstax.org/books/chemistry-2e/pages/5-3-enthalpy">OpenStax Chemistry 2e, Section 5.3: Enthalpy</a>.

Prima legge della termodinamica

Risparmio energetico

L'energia può essere convertita da una forma all'altra, ma tutta l'energia presente prima che si verifichi un cambiamento esiste sempre in qualche forma...

Education

Didattica

JoVE Core

Chimica

Thermochemistry

Termochimica

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

energy conservation and internal energy

Energy conservation describes how energy changes form during chemical and physical changes. Energy can be converted from one form into another, but the energy present before a change still exists in some form after the change is complete. This is the law of conservation of energy. It says energy can neither be created nor destroyed.

The law of conservation of matter also applies during chemical change. In most chemical reactions, the total amount of matter does not show a detectable change. The energy changes are usually modest, and the mass changes are too small to measure. In nuclear reactions, the energy changes are much larger, by factors of a million or so. In those cases, mass changes can be measured, and matter-energy conversion becomes significant.

Substances can also act as reservoirs of energy. Energy can be added to a substance or removed from it. Energy is stored when the kinetic energy of its atoms or molecules increases. That motion can include translation, vibration, or rotation. When thermal energy is lost, those motions slow down, and the kinetic energy decreases.

The total of all possible kinds of energy in a substance is called internal energy, symbolized as U and sometimes as E. As a system changes, its internal energy can change. Energy can move from the system to the surroundings, or from the surroundings to the system. The surroundings then experience an equal and opposite energy change.

Internal energy is a state function, also called a state variable. That means its value depends only on the state of the system, not on how the system got there. Heat and work are not state functions because their values depend on the path taken. Altitude is a useful example of a state function. On Mt. Kilimanjaro, the summit elevation is 5895 m no matter whether someone hiked there or parachuted there. Distance traveled is different, so it is not a state function.

Energy Conservation and Internal Energy

energy basics

How Energy Changes in Chemical Reactions

Chemical reactions change matter and energy at the same time. A match lighting is a simple example. These energy changes are part of everyday life and appear in food, fuels, and industry. Food provides energy through metabolic reactions. The macronutrients in food break down and help keep the body functioning. Fuels such as gasoline, natural gas, and coal are burned to produce energy for transportation, heating, and electricity generation. Industrial chemical reactions also use large amounts...

first law of thermodynamics

Energy conservation describes how energy changes form during chemical and physical changes. Energy can be converted from one form into another, but the energy present before a change still exists in some form after the change is complete. This is the law of conservation of energy. It says energy can neither be created nor destroyed. The law of conservation of matter also applies during chemical change. In most chemical reactions, the total amount of matter does not show a detectable change.

internal energy

Internal Energy, Heat, and Work

Internal energy is the total of all possible kinds of energy in a substance. It is often written as U, and sometimes as E. For a system that changes energy, the important value is the change in internal energy, or ΔU. ΔU is the difference between the final internal energy and the initial internal energy. The exact values of U final and U initial are usually not known, but the first law of thermodynamics only requires ΔU. A positive ΔU means the system gained energy from the surroundings. A...

quantifying heat

Heat Transfer and Specific Heat

Heat transfer and specific heat explain how thermal energy moves and how materials respond to it. Thermal energy is the kinetic energy linked to the random motion of atoms and molecules. Temperature is a measure of how hot or cold a substance is, and it depends on how much thermal energy those particles have. When atoms and molecules move or vibrate faster, their average kinetic energy is higher. That means the object has more thermal energy and a higher temperature. When they move more...

quantifying work

Pressure-Volume Work in Chemistry

Pressure-volume work shows how gas volume changes can transfer energy in chemistry. As a system changes, its internal energy may change too. Energy can move between the system and the surroundings through heat and work. Internal energy, heat, and work are related by an energy equation. Heat depends on a measured temperature change. Work depends on a measured change in volume called pressure-volume work. Work can be defined as a force acting through a distance. Pressure-volume work, also...

enthalpy

Enthalpy and Heat at Constant Pressure

Enthalpy describes heat changes in chemical and physical processes. Chemists use the symbol H for enthalpy. It is defined as a system’s internal energy, E, plus the product of pressure, P, and volume, V. Enthalpy is a state function, so only changes in enthalpy can be measured, not the enthalpy of a substance by itself. For many reactions, the pressure stays constant. Under those conditions, the enthalpy change, ΔH, can be written in a way that includes pressure-volume work. The term PΔV...

thermochemical equations

Heat Changes in Chemical Equations

Heat changes in chemical equations show how much energy a reaction releases or absorbs. At constant pressure, the enthalpy of reaction, or ΔHrxn, is equal to the heat exchanged with the surroundings, qp. Because this value depends on how much reactant takes part, it is an extensive property. The size and sign of ΔHrxn also depend on the reaction itself and on the physical states of the substances involved. An exothermic reaction has a negative ΔHrxn value, while an endothermic reaction has a...

constant pressure calorimetry

Coffee Cup Calorimeter Heat Changes

Coffee cup calorimetry measures heat changes in reactions and physical changes using an insulated calorimeter. The calorimeter is calibrated and designed to limit heat exchange with the outside environment. That makes it possible to measure the heat taken in or released by a substance more accurately, including the energy content of foods. In calorimetry, the system is the substance or substances undergoing change. The surroundings are everything else inside the calorimeter, including the...

constant volume calorimetry

Bomb Calorimeter Heat Measurement

Bomb calorimetry measures the heat released by reactions that produce a lot of energy, especially combustion reactions. A coffee cup calorimeter works at constant pressure and is useful for reactions in solution. A bomb calorimeter works at constant volume and is used for reactions that make large amounts of heat and gaseous products. The word "bomb" refers to the strong, explosive force some reactions can have. In a bomb calorimeter, the volume does not change, so 94V = 0. That means the...

hess's law

Calculating Reaction Heat with Hess's Law

Calculating reaction heat with Hess's law lets chemists find enthalpy changes without measuring every reaction directly. Some reactions are hard or impossible to test in the lab. Even when a reaction can be measured, it is often easier to calculate the heat change from other known enthalpy values. Hess's law says that if a process can be written as the sum of several stepwise processes, the enthalpy change for the total process equals the sum of the enthalpy changes for the steps. This works...

standard enthalpy of formation

Using Standard Enthalpy Values in Chemistry

Enthalpy changes are often listed for reactions that start and end under the same conditions. Chemists use a standard state as a reference set of conditions for comparing properties. In IUPAC terms, the standard state means 1 bar of pressure and 1 M solutions, but it does not set a temperature. Many thermochemical tables still use 1 atm as the reference pressure. Because the difference between 1 bar and 1 atm is very small, enthalpy change usually stays almost the same. A superscripted o in...

enthalpies of reaction

Calculating reaction heat with Hess's law uses standard enthalpies of formation to find the enthalpy change of a reaction. When the formation values for the reactants and products are known, the overall reaction can be broken into simpler stepwise reactions. This approach helps show how the heat change for the full reaction is built from smaller parts. First, the reactants are thought of as being decomposed into their component elements. The enthalpy change for this step is proportional to the...

key terms and concepts

Explore energy conservation, matter changes in chemical and nuclear reactions, and how internal energy, heat, work, and state functions are defined.

Energy Conservation and Internal Energy | JoVE K12

chemistry

JoVE Core: Chimica illustra concetti chiave di chimica attraverso video animazioni concise e di immediata comprensione. Inoltre, i video della sezione "scienziati in azione" mostrano procedure metodologiche realizzate da ricercatori provenienti dai migliori laboratori internazionali.

Louisiana Student Standards for Science

High School

HS-PS3-1

HS-PS3-3

HS-PS3-4

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Tennessee Academic Standards

CHEM1.PS3.4

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.a

Arizona Science Standards

Physical Science

HS.P4

HS.P4U1.8

Texas Essential Knowledge and Skills

CHEM.13

CHEM.13.A

Florida Department of Education

SC.912.P.10

SC.912.P.10.1

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

C-PS3-4

Physics

P-PS3-1

P-PS3-2

P-PS3-3

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Energy

HS-PS3-1.

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
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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

A physical property is ...

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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

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

States of Matter and Phase Changes

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 ...

phase-transitions-vaporization-and-condensation

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

When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules move randomly about, they will occasionally ...

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

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy ...

phase-transitions-sublimation-and-deposition

Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and ...

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.

PS.Chm.7.1

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 ...

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
Differential Scanning Calorimetry (DSC) is a method of thermodynamic analysis based on ...

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.

definition-measurement-pressure-atmospheric-pressure-barometer

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

Gas pressure is caused by force exerted by gas molecules colliding with the surfaces of objects. Although the force of each collision is very small, any ...

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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

Unless individual gases chemically react with each other, the individual gases in a mixture of gases do not affect each other&rsquo;s pressure. Each gas ...

chemical-stoichiometry-gases-using-ideal-gas-law-to-determine

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

Chemical stoichiometry describes the quantitative relationships between reactants and products in chemical reactions.

In addition to measuring quantities ...

basic-postulates-kinetic-molecular-theory-particle-size-energy

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

The ideal-gas equation, which is empirical, describes the behavior of gases by establishing relationships between their macroscopic properties. For ...

kinetic-molecular-theory-gas-laws-explain-properties-gas

Kinetic Molecular Theory and Gas Laws Explain Properties of Gas Molecules

The test of the kinetic molecular theory (KMT) and its postulates is its ability to explain and describe the behavior of a gas. The various gas laws ...

kinetic-molecular-theory-molecular-velocities-temperature-kinetic

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

The kinetic molecular theory qualitatively explains the behaviors described by the various gas laws. The postulates of this theory may be applied in a ...

behavior-gas-molecules-molecular-diffusion-mean-free-path

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

Although gaseous molecules travel at tremendous speeds (hundreds of meters per second), they collide with other gaseous molecules and travel in many ...

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Real Gases: Effects of Intermolecular Forces and Molecular Volume Deriving Van der Waals Equation

Thus far, the ideal gas law, PV = nRT, has been applied to a variety of different types of problems, ranging from reaction stoichiometry and empirical and ...

Ideal Gas Law

Source: Laboratory of Dr. Andreas Z&#252;ttel - Swiss Federal Laboratories for Materials Science and Technology
The ideal gas law describes the behavior ...

Derivation of the Ideal Gas Law
Gases are a fundamental state of matter. A gas is a collection of molecules that have a significant distance between their ...

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.

Energy Conservation and Internal Energy

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