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Questions and Answers
How do the volume changes of gases compare to those of liquids and solids under changes in temperature?
How do the volume changes of gases compare to those of liquids and solids under changes in temperature?
Gas volume changes 50 to 100 times greater than that of liquids and solids when heated or cooled.
What is the relationship between atmospheric pressure and altitude?
What is the relationship between atmospheric pressure and altitude?
Atmospheric pressure decreases with increasing altitude.
Explain the significance of the equation Pressure = force/area in the context of gas pressure.
Explain the significance of the equation Pressure = force/area in the context of gas pressure.
This equation illustrates that gas pressure is determined by the force exerted by gas molecules over a specific area.
What role does a mercury barometer play in measuring atmospheric pressure?
What role does a mercury barometer play in measuring atmospheric pressure?
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Describe how the density of gases changes with cooling.
Describe how the density of gases changes with cooling.
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What is the relationship between gas particle mass, speed, and kinetic energy at a constant temperature?
What is the relationship between gas particle mass, speed, and kinetic energy at a constant temperature?
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How does temperature relate to the average kinetic energy of gas particles?
How does temperature relate to the average kinetic energy of gas particles?
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Explain Graham's Law of Effusion in the context of gas behavior.
Explain Graham's Law of Effusion in the context of gas behavior.
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What is the significance of Avogadro's number in gas behavior at the same temperature?
What is the significance of Avogadro's number in gas behavior at the same temperature?
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Differentiate between effusion and diffusion in gas behavior.
Differentiate between effusion and diffusion in gas behavior.
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How does Charles's Law describe the relationship between volume and temperature of a gas?
How does Charles's Law describe the relationship between volume and temperature of a gas?
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What does Avogadro's Law indicate about the relationship between the volume of a gas and the amount of gas in moles?
What does Avogadro's Law indicate about the relationship between the volume of a gas and the amount of gas in moles?
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What are the standard conditions defined by STP in terms of pressure and temperature?
What are the standard conditions defined by STP in terms of pressure and temperature?
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What is the standard molar volume of an ideal gas at STP?
What is the standard molar volume of an ideal gas at STP?
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What unit of pressure is equivalent to 101.325 kPa?
What unit of pressure is equivalent to 101.325 kPa?
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How does the value of P change according to the van der Waals equation when particle volume increases?
How does the value of P change according to the van der Waals equation when particle volume increases?
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How would you expect the volume of a gas to change if the number of moles decreases while temperature and pressure are held constant?
How would you expect the volume of a gas to change if the number of moles decreases while temperature and pressure are held constant?
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What does the constant 'b' in the van der Waals equation represent?
What does the constant 'b' in the van der Waals equation represent?
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State Boyle's Law in terms of pressure and volume.
State Boyle's Law in terms of pressure and volume.
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In what scenario does the inequality PV/RT > 1 hold true, according to the principles discussed?
In what scenario does the inequality PV/RT > 1 hold true, according to the principles discussed?
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How many millimeters of mercury are equivalent to one atmosphere?
How many millimeters of mercury are equivalent to one atmosphere?
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Define an ideal gas in the context of gas laws.
Define an ideal gas in the context of gas laws.
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Why is the van der Waals equation preferred over the ideal gas law for real gases?
Why is the van der Waals equation preferred over the ideal gas law for real gases?
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What effect do the constants 'a' and 'b' have on the properties of different gases as seen in the van der Waals equation?
What effect do the constants 'a' and 'b' have on the properties of different gases as seen in the van der Waals equation?
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What happens to the pressure of a gas if its volume is decreased at constant temperature?
What happens to the pressure of a gas if its volume is decreased at constant temperature?
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What is the conversion from 1 bar to pascals?
What is the conversion from 1 bar to pascals?
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In the context of the gas laws, what are the four variables that describe the behavior of gases?
In the context of the gas laws, what are the four variables that describe the behavior of gases?
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What is the relationship between temperature and gas pressure when volume is held constant?
What is the relationship between temperature and gas pressure when volume is held constant?
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What factors contribute to real gases deviating from ideal gas behavior?
What factors contribute to real gases deviating from ideal gas behavior?
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At what conditions do real gases deviate most significantly from ideal behavior?
At what conditions do real gases deviate most significantly from ideal behavior?
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How does particle volume affect the behavior of real gases at moderately high pressure?
How does particle volume affect the behavior of real gases at moderately high pressure?
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What effect do interparticle attractions have on gas pressure as external pressure increases?
What effect do interparticle attractions have on gas pressure as external pressure increases?
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Describe the significance of the molar volume of gases at standard temperature and pressure (STP).
Describe the significance of the molar volume of gases at standard temperature and pressure (STP).
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What happens to the pressure of a gas as the external pressure increases and why?
What happens to the pressure of a gas as the external pressure increases and why?
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How do attractive and repulsive forces between gas particles influence their behavior?
How do attractive and repulsive forces between gas particles influence their behavior?
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What role does the size of gas particles play in deviations from ideal gas behavior?
What role does the size of gas particles play in deviations from ideal gas behavior?
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Study Notes
Gases and the Kinetic Molecular Theory
- Gases, unlike liquids and solids, have volumes that change significantly with pressure and temperature.
- Gas volume expands when heated and shrinks when cooled; this change is much greater than that of liquids and solids.
- Gases flow freely and have relatively low densities; gas density increases when cooled.
- Gases form solutions in any proportions and are freely miscible with each other.
Application of the Gas Laws: Breathing
- For air to move in and out of the lungs, the pressure inside the lungs must change, forcing the lungs to change volume.
- Inhalation involves expanding the lungs; decreasing pressure in the lungs causes air to flow in.
- Exhalation involves shrinking the lungs; increasing pressure in the lungs forces air out.
11: Gases and the Kinetic Molecular Theory
- Sections 11.1-11.6 discuss various aspects of gases and their behavior, from physical states to real-gas deviations.
The Three States of Matter
- Gases: particles are far apart, move freely, filling the available volume.
- Liquids: particles are close together but can move around each other.
- Solids: particles are close together in a fixed, regular arrangement and do not move around freely.
An Overview of the Physical States of Matter
- Gas volume changes significantly with pressure.
- Solid and liquid volumes are not greatly affected by pressure.
- Gases expand when heated and shrink when cooled.
- Volume change for gases is significantly greater than for liquids and solids (50-100 times).
- Gases flow easily and have low densities.
- Gas density increases as the gas cools.
- Gases mix in any proportions.
- Gases are miscible with each other.
Gas Pressure
- Atmospheric pressure arises from the force exerted by atmospheric gases on Earth's surface.
- Atmospheric pressure decreases with altitude.
- Pressure is defined as force over area.
A Mercury Barometer
- A barometer measures atmospheric pressure.
- At sea level, the column of Hg exerts the same pressure on the Hg surface as the atmosphere does.
- Atmospheric pressure is often measured in units of mmHg, torr, atm, Pa, kPa, etc.
Common Units of Pressure
- Common units for pressure include pascals (Pa), kilopascals (kPa), atmospheres (atm), millimeters of mercury (mmHg), torr, and pounds per square inch (psi).
The Gas Laws
- Gas laws describe the physical behavior of gases through pressure (P), temperature (T), volume (V), and amount (n).
- Three gas laws look at the effect of one variable on another while keeping the other two constant.
- Ideal gases exhibit linear relationships among variables.
Boyle's Law
- At constant temperature, the volume of a fixed amount of gas is inversely proportional to the external pressure.
- Pressure and volume are inversely proportional (PV = constant).
Charles's Law
- At constant pressure, the volume of a fixed amount of gas is directly proportional to its absolute temperature.
- Volume and temperature are directly proportional (V/T = constant).
Avogadro's Law
- At constant temperature and pressure, equal volumes of any ideal gas contain equal numbers of particles (moles).
- Volume and amount are directly proportional (V/n = constant).
Gas Behavior at Standard Conditions
- Standard Temperature and Pressure (STP) is defined as 0 °C and 1 atm (760 torr).
- The standard molar volume of an ideal gas at STP is 22.4 L/mol.
Gay-Lussac's Law
- At constant volume, the pressure of a fixed amount of gas is directly proportional to its absolute temperature.
The Ideal Gas Law
- The ideal gas law (PV = nRT) relates pressure (P), volume (V), amount (n), and temperature (T) of an ideal gas.
- The gas constant (R) depends on the units used.
- For one mole of a gas at STP, R = 0.0821 L·atm/mol·K or 8.314 J/mol·K.
Individual Gas Laws as Special Cases
- Boyle's, Charles', and Avogadro's Laws are special cases of the ideal gas law.
Application of the Gas Laws: Breathing
- Boyle's law explains breathing mechanics.
- Changing lung volume changes pressure, causing air to flow in or out.
Sample Problem 1
- Provides an example of applying the ideal gas law principles to calculate helium mass increase to create a blimp.
The Ideal Gas Law and Gas Density
- Gas density (d) is related to molar mass (M), pressure (P), and temperature (T) by the ideal gas law.
The Ideal Gas Law and Molar Mass
- The ideal gas law can be used to calculate molar mass.
Mixtures of Gases
- Gases mix homogeneously in any proportion.
- Dalton's law of partial pressures states that the total pressure in a mixture is the sum of the partial pressures of the component gases.
Air Composition
- Percentage composition of dry air by volume is approximately 21% O2, 78% N2, and 1% Ar.
- Calculating the average molar mass of dry air.
The Ideal Gas Law and Stoichiometry
- The ideal gas law combines to relate gas amounts in chemical reactions.
Sample Problem 2
- An example of using gas laws for stoichiometry problems
Kinetic-Molecular Theory
- Describes gas behavior from a microscopic standpoint.
- Five postulates cover the behavior of gas particles.
- Kinetic energy is the total energy of motion in a system of particles.
Molecular Speed
- Each gas particle has a molecular speed.
- The most probable speed of gas particles increases with temperature.
- The average kinetic energy (Ek) and temperature (T) are related (Ek = c × T).
Molar Mass and Molecular Speed
- The most probable molecular speed increases when molar mass decreases (lighter molecules are faster).
- Gases with low molar masses exhibit faster speeds because a lighter molecule needs less energy to reach a given velocity.
Molecular View of the Gas Laws
- A visualization of the kinetic molecular theory and gas laws, explaining how changes in volume (Boyle's), temperature (Charles',), amount (Avogadro's), or gas identity (Dalton's) affect a gas sample.
Kinetic Energy and Gas Behavior
- All gases at the same temperature share the same average kinetic energy.
- Kinetic energy of gas particles is proportional to the absolute temperature of the gas; the average speed of the particles differs according to their molar mass.
- Temperature measures average kinetic energy.
Graham's Law of Effusion
- Effusion is the escape of a gas through a small opening into a vacuum.
- Diffusion is the mixing of gases due to random motion.
- Rate of effusion is inversely proportional to the square root of its molar mass.
Real Gases: Deviations from Ideal Behavior
- Ideal gas models do not account for the volume of gas particles or their inter-particle attractive and repulsive forces.
- Real gas behavior deviates from ideal gas behavior most substantially at low temperatures and high pressures.
Molar Volume of Some Common Gases
- Molar volume data for several common gases at STP.
- Comparison reveals how different gases exhibit varying conditions under STP.
Deviations With Increasing External Pressure
- Deviations from ideal gas behavior are apparent when using PV/RT values; higher external pressures lead to an increase from ideal PV/RT.
- Effect of inter-particle attractions and particle volume leads to non-ideal gas behavior.
Effect of Interparticle Attractions
- At moderate pressures, interparticle attractions between gas particles lower the force of collisions with the container walls.
- Lowering the force decreases the gas pressure because PV/RT < 1.
Effect of Particle Volume
- At very high pressures, the free volume between gas particles is less than the container volume, so interparticle volume becomes significant resulting in PV/RT > 1.
Van der Waals Equation
- Corrects the ideal gas law to account for particle volume and interparticle attractions (using constants 'a' and 'b').
Van der Waals Constants
- Compilation of 'a' and 'b' constants for several common gases. These constants are used in the van der Waals equation.
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Description
Test your understanding of gas laws and properties with this comprehensive quiz. Explore the relationships between temperature, volume, pressure, and gas behavior while learning about concepts such as Graham's Law, Avogadro's number, and the significance of mercury barometers. Perfect for students studying chemistry or physics.
