Real Gases

Real Gases The Kinetic Molecular Theory describes the properties of ideal gases. Recall the tenets of the Kinetic Molecular Theory: A gas consists of a collection of small particles that travel in straight-line motion and obey Newton’s Laws. Gas particles occupy no volume. Collisions between particles are perfectly elastic, meaning that no energy is gained…

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Graham’s Law of Effusion of Gases

Graham’s Law of Effusion Before we talk about Graham’s Law of Effusion, let’s explore what effusion is and distinguish it from diffusion. Effusion is the movement of one type of gas particles through a hole.   Diffusion, on the other hand, is the movement of particles from areas of high concentration to areas of low…

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Root Mean Square Velocity of a Gas

Root Mean Square Velocity You already know that the velocity (or speed) of gas particles increases with increasing temperature. Another factor affecting the velocity of gas particles is their size — specifically, their molar mass. The following equation relates the speed of gas particles to both temperature and molar mass.   where rms represents root…

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Average Kinetic Energy of a Gas

Average Kinetic Energy of a Gas The Kinetic Energy, also known as the energy of motion, of gas particles is directly proportional to temperature. The higher the temperature, the more kinetic energy the particles have. Another way of saying this is that, the higher the temperature, the faster the particles move. This relationship between kinetic…

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Kinetic Molecular Theory

Kinetic Molecular Theory Kinetic Molecular Theory is a set of basic assumptions about gas particles that allows us to predict their behavior fairly accurately. These are the four tenets of Kinetic Molecular Theory (KMT): The particles in a gas are small and very far apart. Most of a gas’s volume is empty space. Gas particles…

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Partial Pressure and Mole Fraction

Partial Pressure and Mole Fraction Mole fraction is the ratio of the number of moles of one component in a mixture to the total number of moles in the mixture. In the case of a mixture of gases, the mole fraction of one particular gas would equal the number of moles of that gas divided…

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Dalton’s Law of Partial Pressure Collecting Gas over Water

Dalton’s Law of Partial Pressure allows us to determine the pressure (and from that, concentration) of a gas produced in a chemical reaction by collecting the gas over water. When gas is collected over water, the gas displaces the water in the flask as depicted above. The volume the gas displaces the water is the…

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Gas Stoichiometry

Gas Stoichiometry The ideal gas law can be used to determine the number of moles of a gas given pressure, volume and temperature. The number of moles of a gas in a chemical equation can be used to determine the number of moles of any other species in the same reaction. Hence, we can use…

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Ideal Gas Law and Density of a Gas

Ideal Gas Law and Density of a Gas The Ideal Gas Law can also be used to determine the density of a gas. To derive that equation, we begin with the ideal gas law: (1)    Density is defined as mass per unit volume. (2)   Recall that we also derived the equation for the…

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Ideal Gas Law and Molar Mass of a Gas

Ideal Gas Law and Molar Mass of a Gas The ideal gas law can be used to determine the molar mass of a gas. Recall that molar mass has the units grams per mole. Given the volume, pressure and temperature of a gas, we can use the ideal gas law to determine the number of…

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The Ideal Gas Law and Mass

The ideal gas law can tell us the number of moles of a gas, given its volume, pressure and temperature. Once we know the number of moles, we can calculate the mass of a gas by multiplying the number of moles by molar mass. Let’s do just that. Sample Problem How many grams of chlorine…

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Ideal Gas Law

Ideal Gas Law One mole of ANY gas at standard temperature and pressure occupies a volume of 22.414 L. Recall that standard temperature is 0°C or 273.15 K, and that standard pressure is 1 atm. But what about gases that are NOT at STP? What volume do these gases take up? We can determine that…

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Avogadro’s Hypothesis

Avogadro’s Hypothesis Avogadro’s Hypothesis says that equal volumes of gases at the same temperature and pressure contain the same number of moles. In other words, a mole of oxygen molecules with a molar mass 32.00 g/mol and a mole of radon atoms with a molar mass of 222 g/mol occupy the same volume at equal…

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Combined Gas Law

Combined Gas Law The three gas laws Charles’s Law, Boyle’s Law and Gay-Lussac’s Law can be combined into one combined gas law relating pressure, volume and temperature of a gas. The combined gas law is: We’ll learn how to use this equation by considering some sample problems. Sample Problem Carbon dioxide occupies a 2.54 L…

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Standard Temperature and Pressure (STP)

Chemists define the standard temperature and pressure of gases, abbreviated STP, as 0 ºC and 1 atm pressure. Recall that 0 ºC is equal to 273.15 Kelvin. Standard Pressure = 1 atm = 760 mm Hg = 101.3 kPa Click here to learn how to convert among pressure units. Click here to learn how to…

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Temperature Conversion between Kelvin and Celsius

The unit of temperature for all gas problems is Kelvin. Whereas the celsius scale is based on the boiling point and freezing point of water, 0 ºC and 100 ºC respectively, the Kelvin scale is based on the lowest possible temperature absolute zero, which is 0 K. There are no negative numbers in the Kelvin…

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Gay Lussac’s Law

Gay-Lussac’s Law Gay-Lussac’s Law says that gas pressure is directly proportional to gas temperature when volume is held constant. The equation is: Gay-Lussac’s law says that, as you increase the pressure of a gas, its temperature also increases, if volume is held constant. As you increase the temperature of a gas, its pressure also increases.…

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Charles’s Law

Charles’s Law Charles’s Law says the gas volume is directly related to gas temperature. As the temperature of a gas increases, so does its volume. And as the volume of a gas increases, so does its temperature.   V1 is the initial volume, T1 is the initial temperature and V2 is the new volume, and…

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Boyle’s Law

Boyle’s Law Boyle’s Law says that gas volume is inversely proportional to gas pressure when we hold temperature constant. Inversely proportional means that, as you increase one, the other decreases, and vice versa. As you increase the pressure of a gas, its volume decreases. And as you decrease the volume of a gas its pressure…

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Dalton’s Law of Partial Pressure

Dalton’s Law of Partial Pressure says that the total pressure of a mixture of gases equals the sum of the pressures that each would exert if it was present alone. The equation for Dalton’s Law of Partial Pressure is: the total pressure of a mixture of gases is equal to the pressure of gas A…

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Kinetic Molecular Theory of Gases

Kinetic Molecular Theory of Gases The behavior of gases that we study in basic chemistry is based on the following four assumptions, known collectively as the Kinetic Molecular Theory of motion. Making these assumptions allows us to predict properties of gases that hold true most of the time. They are: A gas consists of a…

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How to Convert Units of Gas Pressure

Pressure is measured in many different units, including millimeters mercury (mm Hg), atmospheres (atm), Torr, Pascals , pounds per square inch (psi) and Bar. The conversion factors among these units are as follows: A Torr is equal to mm Hg, named in order of Evangelista Torricelli, the creator of the first barometer. Let’s do some…

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Reading a Barometer and Manometer

How to Read a Barometer The barometer was developed by Evangelista Torricelli in 1643. It measures atmospheric pressure. Atmospheric pressure pushes down on the mercury in the basin, causing the column to rise. The height of the column is equal to the Atmospheric Pressure. Atmospheric Pressure, then, is measured by measuring the height of the…

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Gas Pressure

The concentration of gases is most often expressed as Gas Pressure. Pressure is defined as force per unit area. The equation for pressure is: P = pressure F = force A = area Gas Pressure is the force gases exert on their container per unit area. This equation can be rewritten to solve for either…

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