Name: pressure units and tools for gas measurement
Uploaded: 2020-09-03T13:38:26.000Z
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K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Chemistry

Energy

PS.Chm.7.3

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

Recordemos que um gás assume sempre a forma e volume do recipiente em que está contido. Microscopicamente, um gás consiste em partículas em movimento que colidem entre si e com as paredes do seu recipiente. Cada colisão com a parede exerce uma pequena força na área de contato.As forças resultantes de um grande número de colisões deste tipo adicionam-se à sua pressão. Menos partículas de gás levam a menos colisões, uma força mais baixa por unidade de área e, portanto, uma pressão mais baixa. A pressão, portanto, é diretamente proporcional ao número de partículas num determinado volume, ou à densidade do gás.O ar uma mistura de diferentes átomos gasosos e moléculas exerce pressão sobre tudo o que se encontra à superfície da terra. Isto é a pressão atmosférica e é medida através de um barômetro. Um barômetro tradicional é um tubo de vidro cheio de mercúrio que é invertido num prato que contém mercúrio.Em resposta à pressão exercida pela atmosfera, na altura da coluna de mercúrio sobe ou desce. Medir a altura fornece uma medida da pressão atmosférica. Ao nível do mar, a pressão atmosférica é 1 de pressão atmosférica, o que eleva na coluna de mercúrio a uma altura de 760 milímetros de mercúrio.A altitudes mais elevadas, onde o ar é menos denso, na altura da coluna de mercúrio cai, indicando uma descida da pressão atmosférica. A pressão de um gás aprisionado num recipiente é medido através de um manômetro. Um manômetro fechado consiste num tubo em U cheio de mercúrio.Uma extremidade é selada no vácuo e a outra extremidade está ligada ao recipiente que é cheio com a amostra de gás. As partículas de gás empurram para baixo o mercúrio numa das extremidades do tubo, criando uma diferença de altura que corresponde à pressão exercida pelo gás. Num manômetro de extremidade aberta, uma extremidade é deixada aberta para a atmosfera.Isto mede a pressão da amostra de gás no que diz respeito à pressão atmosférica. Quando o gás exerce uma pressão mais elevada do que a pressão atmosférica, a diferença de altura é adicionada à pressão atmosférica. Isto produz a pressão do gás.Inversamente, quando a atmosfera exerce uma pressão maior do que a amostra de gás, a diferença de altura é subtraída à pressão atmosférica para obter a pressão do gás.

pressão e medição da pressão

A pressão do gás é causada pela força exercida pelas moléculas de gás que colidem com as superfícies dos objetos. Embora a força de cada colisão seja muito pequena, qualquer superfície com uma área considerável sofre um grande número de colisões em um curto espaço de tempo, o que pode resultar em alta pressão.

No geral, a pressão é definida como a força exercida sobre uma determinada área: 

<img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/1035/1035_Equations-01.png" style="height: 40px;" />

A pressão é diretamente proporcional à força e inversamente proporcional à área. Assim, a pressão pode ser aumentada, quer aumentando a quantidade de força, quer diminuindo a área sobre a qual é aplicada; a pressão pode ser diminuída diminuindo a força ou aumentando a área.

A unidade SI de pressão é o pascal (Pa), com 1 Pa = 1 N/m2, onde N é o newton, uma unidade de força definida como 1 kg·m/s2. Um pascal é uma pequena pressão; em muitos casos, é mais conveniente utilizar unidades de quilopascal (1 kPa = 1000 Pa) ou bar (1 bar = 100.000 Pa). A pressão também pode ser medida utilizando a unidade atmosfera (atm). 

<h4>Medição da Pressão</h4>

A pressão atmosférica, a força exercida pela atmosfera na superfície da terra, é medida com um barómetro. Um barómetro é um tubo de vidro fechado em uma extremidade, cheio de líquido não volátil, como mercúrio, e depois invertido e imerso em um recipiente desse líquido. A atmosfera exerce pressão sobre o líquido fora do tubo, a coluna de líquido exerce pressão dentro do tubo, e a pressão na superfície do líquido é a mesma dentro e fora do tubo. A altura do líquido no tubo é, portanto, proporcional à pressão exercida pela atmosfera.

No barómetro, o mercúrio é a escolha preferida em vez de água, uma vez que é 13,5 vezes mais denso do que a água. A pressão atmosférica pode suportar uma coluna de mercúrio com apenas cerca de 0,760 m de altura, enquanto que uma coluna de água teria de ter 10,3 m de altura. Isto torna uma coluna de mercúrio uma forma conveniente de medir a pressão.

A pressão atmosférica padrão de 1 atm ao nível do mar (101.325 Pa) corresponde a uma coluna de mercúrio com cerca de 760 mm (29,92 pol.) de altura. A pressão exercida por um fluido devido à gravidade é conhecida como pressão hidrostática, p:

<img alt="Eq2" src="https://www.jove.com/files/core/CDNSource/lessons/1035/1035_Equations-02.png" style="height: 40px;" />

em que h é a altura do fluido, ρ é a densidade do fluido, e g é a aceleração devido à gravidade.

Um manómetro é um dispositivo utilizado para medir a pressão de um gás preso em um recipiente. Um manómetro de extremidade fechada é um tubo em forma de U com um braço fechado, um braço que se liga ao gás a ser medido, e mercúrio no meio. A distância entre os níveis de líquido nos dois braços do tubo, h, é proporcional à pressão do gás no recipiente. Em um manómetro de extremidade aberta, um braço do tubo está aberto à atmosfera. Neste caso, a distância entre os níveis de líquido corresponde à diferença de pressão entre o gás no recipiente e a atmosfera. 

Este texto é adaptado de <a href="https://openstax.org/books/chemistry-2e/pages/9-1-gas-pressure">Openstax, Chemistry 2e, Section 9.1: Gas Pressure</a>.

Pressão e Medição da Pressão

A pressão do gás é causada pela força exercida por moléculas de gás que colidem com as superfícies dos objetos. Embora a força de cada colisão seja muito pequena, qualquer ...

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Química

Gases

KEY TERMS AND CONCEPTS

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pressure units and tools for gas measurement

Pressure is the force applied to a given area, and gas pressure comes from gas molecules colliding with surfaces. Each collision is tiny, but many collisions over a small area can create high pressure. Pressure increases when force increases or when the area gets smaller. It decreases when force drops or when the area gets larger.

Pressure is measured in pascals, or Pa, in the SI system. One pascal equals 1 newton per square meter, and a newton is a unit of force equal to 1 kg·m/s2. A pascal is a small unit, so kilopascal (kPa) and bar are often more useful. Pressure can also be reported in atmospheres, or atm.

Atmospheric pressure is the force the atmosphere exerts on Earth’s surface. It is measured with a barometer. A barometer uses a glass tube that is closed at one end, filled with a nonvolatile liquid such as mercury, and then turned upside down in a container of the same liquid. The atmosphere presses on the liquid outside the tube, and the liquid column inside the tube rises to a height that matches that pressure.

Mercury is preferred in a barometer because it is 13.5 times denser than water. That means atmospheric pressure supports only about 0.760 m of mercury, while a water column would need to be 10.3 m tall. Standard atmospheric pressure at sea level is 1 atm, or 101,325 Pa, and it corresponds to a mercury column about 760 mm, or 29.92 in., high.

Fluid pressure from gravity is called hydrostatic pressure. It depends on the height of the fluid, its density, and the acceleration due to gravity. A manometer uses this idea to measure gas pressure in a container. A closed-end manometer has one sealed arm, one arm connected to the gas, and mercury between them. The height difference between the liquid levels gives the gas pressure.

An open-end manometer has one arm open to the atmosphere. In that setup, the height difference shows the pressure difference between the trapped gas and the air around it. Together, barometers and manometers show how fluid height can be used to measure atmospheric pressure and gas pressure.

Pressure Units and Tools for Gas Measurement

pressure-units-and-tools-for-gas-measurement

definition and measurement of pressure: atmospheric pressure, barometer, and manometer

Pressure is the force applied to a given area, and gas pressure comes from gas molecules colliding with surfaces. Each collision is tiny, but many collisions over a small area can create high pressure. Pressure increases when force increases or when the area gets smaller. It decreases when force drops or when the area gets larger. Pressure is measured in pascals, or Pa, in the SI system. One pascal equals 1 newton per square meter, and a newton is a unit of force equal to 1 kg·m/s2. A pascal...

gas laws: boyle's, gay-lussac, charles', avogadro's, and ideal gas law

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How Gas Pressure, Volume, and Temperature Change

Gas pressure, volume, temperature, and amount are linked by several gas laws. Scientists found these relationships by studying how a confined gas changes when one variable is held constant and another changes. These patterns apply to an ideal gas, which is a useful model for gases under low pressure and high temperature. Gay-Lussac’s law, also called Amontons’s law, connects pressure and temperature. If gas is trapped in a rigid container, the volume and number of moles stay constant. When the...

applications of the ideal gas law: molar mass, density, and volume

applications-of-the-ideal-gas-law-molar-mass-density-and-volume

Ideal Gas Law at STP and Gas Density

The ideal gas law links pressure, volume, number of moles, and temperature. It helps explain how gas volume changes when pressure or temperature changes. At standard temperature and pressure, or STP, the values are 273.15 K and 1 atm. At STP, one mole of an ideal gas occupies about 22.4 L. This is called the standard molar volume. The gas can be hydrogen, oxygen, argon, or carbon dioxide, and the volume is still about 22.4 liters. Half a mole occupies 11.2 L, and 2 moles occupy 44.8 L. The...

mixtures of gases: dalton's law of partial pressures and mole fractions

mixtures-of-gases-dalton-s-law-of-partial-pressures-and-mole-fractions

Gas Pressure in Mixtures: Partial Pressures

Gas pressure in mixtures is described by partial pressure and mole fraction. When gases do not chemically react, each gas in the mixture acts as if it were alone in the container. The pressure from one gas is called its partial pressure. For a mixture of three gases, A, B, and C, the total pressure equals the sum of their partial pressures: PA, PB, and PC. This is Dalton's law of partial pressures. It states that the total pressure of a mixture of ideal gases is the sum of the pressures from...

chemical stoichiometry and gases: using ideal gas law to determine moles

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Stoichiometry of Gases with the Ideal Gas Law

Chemical stoichiometry links the amounts of reactants and products in a chemical reaction. For gases, those amounts can also be measured by volume. If a gas’s volume, pressure, and temperature are known, the ideal gas equation can be used to find the number of moles present. The same idea works in reverse. If the moles of a gas are known, its volume can be found at any temperature and pressure. The transcript gives an example using 8.88 g of gallium reacting with excess hydrochloric acid.

basic postulates of kinetic molecular theory: particle size, energy, and collision

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Kinetic Molecular Theory and Gas Behavior

Kinetic molecular theory explains gas behavior at the particle level. It gives a microscopic model for what happens when pressure or temperature changes. Gas laws describe how macroscopic properties change, but they do not explain why those changes happen. The theory was put into a complete form by Rudolf Clausius in 1857. It was built from hundreds of experimental observations about gases. Those observations helped explain the different gas laws through a few basic postulates. One key idea...

kinetic molecular theory and gas laws explain properties of gas molecules

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Gas Pressure Patterns in Kinetic Molecular Theory

Kinetic molecular theory explains gas pressure by linking it to the motion of gas molecules. Gas pressure comes from rapidly moving molecules hitting the walls of a container. It depends on how many molecules strike a unit area in a given time. The theory also helps explain the main gas laws. In Gay-Lussac’s law, also called Amontons’s law, raising temperature increases the average speed and kinetic energy of gas molecules. If volume stays constant, the molecules collide with the walls more...

kinetic molecular theory: molecular velocities, temperature, and kinetic energy

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Gas Particle Speed Distributions and Temperature

Gas particle speed distributions and temperature are key ideas in the kinetic molecular theory. This theory explains the gas laws by describing how gas molecules move, collide, and share energy. Gas molecules do not all move at the same speed. A gas sample has an average speed and an average kinetic energy, but individual molecules move at different speeds. Their collisions are elastic, which means momentum is conserved. Because so many molecules collide, the overall speed distribution stays...

behavior of gas molecules: molecular diffusion, mean free path, and effusion

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Gas Particle Motion, Diffusion, and Effusion

Gas particle motion, diffusion, and effusion explain how gases spread and escape in everyday settings. Gas molecules move at very high speeds, but they collide with other gas molecules and change direction many times before reaching a target. At room temperature, a gas molecule can experience billions of collisions each second. The mean free path is the average distance a molecule travels between collisions. This distance becomes larger when pressure decreases. In general, the mean free path...

real gases: effects of intermolecular forces and molecular volume deriving van der waals equation

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Real Gases: When the Ideal Gas Law Breaks Down

Real gases are gases that do not always follow the ideal gas law, PV = nRT, especially when pressure is high or temperature is low. The ideal gas model assumes gas particles have no attractive or repulsive forces and take up negligible space compared with the container. At room temperature and 1 atm or less, many gases behave close to ideally. When conditions change, the measured relationships between pressure, volume, and temperature can drift away from the ideal prediction. One way to see...

key terms and concepts

Learn how pressure is measured with pascals, atmospheres, barometers, and manometers, plus why mercury columns show atmospheric and gas pressure.

Pressure Units and Tools for Gas Measurement | JoVE K12

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Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Gas laws

Virginia  Standards of Learning

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CH.6

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Earth Science

ES.11

ES.11.a

Arizona Science Standards

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Physical Science

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CHEM.10

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Matter and Its Interactions

9-12.C.1.4.e

9-12.C.4.7.b

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New York State Science Learning Standards

HS. Structure and Properties of Matter

HS-PS1-9.

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

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

Particles in a solid are tightly packed together (fixed shape) and often arranged in a regular pattern; in a liquid, they are close together with no ...

Intermolecular vs Intramolecular Forces

Intermolecular forces (IMF) are electrostatic attractions arising from charge-charge interactions between molecules. The strength of the intermolecular ...

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 ...

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 ...

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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

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 ...

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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 ...

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 ...

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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.

PS.Chm.7.2

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 ...

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 ...

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 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 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 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, 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 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 ...

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 ...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Preparation of the LaboratoryExpand
	Here, we show the laboratory preparation for 10 students ...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Determining the Mass of the Unknown LiquidExpand
	According to the ideal gas law for a given ...

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

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

Pressure Units and Tools for Gas Measurement

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