Gases and Gas Laws
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Questions and Answers

A gas has well-defined boundaries and does not diffuse to fill any container.

False (B)

The freezing point of water is 100°C on the Celsius scale.

False (B)

Normal atmospheric pressure is approximately 1 x 105 Pa.

True (A)

Boyle's Law states that the volume of a fixed mass of gas is directly proportional to its pressure at constant temperature.

<p>False (B)</p> Signup and view all the answers

1 litre is equivalent to 1000 cm³.

<p>True (A)</p> Signup and view all the answers

The SI unit of volume is the cubic millimeter (mm³).

<p>False (B)</p> Signup and view all the answers

Absolute zero is defined as 0 K and corresponds to -273°C.

<p>True (A)</p> Signup and view all the answers

The pressure exerted by a gas on its container is measured in pascals (Pa).

<p>True (A)</p> Signup and view all the answers

Boyle's Law states that pressure and volume of a gas are directly proportional when temperature is constant.

<p>False (B)</p> Signup and view all the answers

Jacques Charles discovered that the volume of a fixed mass of gas is directly proportional to its temperature at constant pressure.

<p>True (A)</p> Signup and view all the answers

The equation $V/T = k$ represents Charles' Law, where $V$ is volume and $T$ is temperature.

<p>True (A)</p> Signup and view all the answers

According to Charles' Law, the graph of volume against temperature should pass through the origin.

<p>False (B)</p> Signup and view all the answers

For a gas, if the pressure increases, the volume must decrease, provided the temperature is constant.

<p>True (A)</p> Signup and view all the answers

The absolute zero temperature is approximately -273°C, below which gas volume theoretically becomes zero.

<p>True (A)</p> Signup and view all the answers

In Boyle's Law, the product of pressure and volume remains constant only when temperature changes.

<p>False (B)</p> Signup and view all the answers

The relationship between the temperature in Celsius and the volume of gas can be described using an exponential equation.

<p>False (B)</p> Signup and view all the answers

According to the Combined Gas Law, $p_1V_1 = p_2V_2$ is valid only when temperature is constant.

<p>True (A)</p> Signup and view all the answers

Gay-Lussac's Law states that equal volumes of gases contain different numbers of molecules under the same conditions.

<p>False (B)</p> Signup and view all the answers

At standard temperature and pressure (s.t.p), one mole of any gas occupies a volume of 22.4 litres.

<p>True (A)</p> Signup and view all the answers

The formula for finding the final volume in the Combined Gas Law is $V_2 = \frac{p_1V_1T_2}{p_2T_1}$.

<p>False (B)</p> Signup and view all the answers

Boyle's Law establishes a relationship between pressure and temperature while keeping volume constant.

<p>False (B)</p> Signup and view all the answers

From the example of nitrogen gas, the final volume $V_2$ calculated was 64.84 cm³.

<p>True (A)</p> Signup and view all the answers

Avogadro's Law implies that gases behave identically under varying conditions.

<p>False (B)</p> Signup and view all the answers

At room temperature and pressure, one mole of any gas occupies a volume of 24.0 litres.

<p>True (A)</p> Signup and view all the answers

An ideal gas perfectly obeys all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure.

<p>True (A)</p> Signup and view all the answers

Attractive forces between gas molecules do not exist in the assumptions of the kinetic theory of gases.

<p>True (A)</p> Signup and view all the answers

The volume of gas molecules is significant compared to the distances between them according to the kinetic theory of gases.

<p>False (B)</p> Signup and view all the answers

All collisions between gas molecules are assumed to be perfectly elastic.

<p>True (A)</p> Signup and view all the answers

The average kinetic energy of gas molecules is directly proportional to temperature measured on the Celsius scale.

<p>False (B)</p> Signup and view all the answers

The equation of state for an ideal gas is represented as $pV = NRT$.

<p>True (A)</p> Signup and view all the answers

In the experiment to measure the relative molecular mass of a volatile liquid, the flask is heated to a temperature of 100 °C.

<p>False (B)</p> Signup and view all the answers

In the gas law equation, the universal gas constant R is equal to 8.3 J K-1 mol-1.

<p>True (A)</p> Signup and view all the answers

The number of moles of gas present in a sample containing $1.8 \times 10^{24}$ atoms of chlorine at s.t.p. is 2 moles.

<p>False (B)</p> Signup and view all the answers

When the flask appears to be empty, it indicates that all the volatile liquid has vaporised.

<p>True (A)</p> Signup and view all the answers

Real gases behave ideally under all conditions of temperature and pressure.

<p>False (B)</p> Signup and view all the answers

The atmospheric pressure inside the flask becomes lower than the atmospheric pressure outside before the liquid fully vaporises.

<p>False (B)</p> Signup and view all the answers

Avogadro's law states that equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

<p>True (A)</p> Signup and view all the answers

Cyclohexane is an unsuitable liquid for the experiment described.

<p>False (B)</p> Signup and view all the answers

A mass spectrometer can accurately measure the relative molecular masses of volatile and non-volatile liquids as well as solids and gases.

<p>True (A)</p> Signup and view all the answers

The mass of the vapor can be determined by subtracting the final mass of the flask and fittings from the initial mass.

<p>True (A)</p> Signup and view all the answers

Non-volatile liquids vaporize easily, making them suitable for relative molecular mass calculations using the described method.

<p>False (B)</p> Signup and view all the answers

The volume of the flask is found by measuring how much water it can hold.

<p>True (A)</p> Signup and view all the answers

The vapor of 0.63 g of a pure liquid occupies a volume of 330 cm3 at a pressure of 1010 kPa.

<p>False (B)</p> Signup and view all the answers

Droplets of liquid form inside the conical flask as it cools down after heating.

<p>True (A)</p> Signup and view all the answers

The pressure of the vapor inside the flask can be lower than the atmospheric pressure due to the pinhole.

<p>False (B)</p> Signup and view all the answers

Flashcards

Gaseous state of matter

A state of matter with no defined boundaries that rapidly fills any container.

Temperature (Kelvin)

Measure of heat, using Kelvin scale with 0 K as absolute zero.

Pressure (Gas)

Force exerted by a gas on a unit area.

Boyle's Law

At constant temperature, gas volume is inversely proportional to pressure.

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Standard Temperature and Pressure (STP)

Standard conditions for gas measurements: 273 K and 100,000 Pa.

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Volume of a gas

Equals the volume of the container holding it.

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Inverse relationship (Boyle's Law)

As pressure increases, volume decreases, and vice versa (at constant temperature).

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SI unit for Volume

Cubic metre (m³)

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Boyle's Law Equation

pV = k, where p is pressure, V is volume, and k is a constant at a fixed temperature.

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Charles' Law

At constant pressure, the volume of a fixed mass of gas is directly proportional to its temperature (in Kelvin).

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Charles' Law Equation

V/T = k, where V is volume, T is temperature in Kelvin, and k is a constant at a fixed pressure.

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Absolute Zero

-273.15°C, the theoretical temperature at which the volume of a gas would be zero if it followed Charles' Law.

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Kelvin Scale

A temperature scale where 0 Kelvin represents absolute zero, and the size of a degree is the same as a degree Celsius.

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Fixed Mass of Gas

A specific amount of gas whose properties (like number of gas particles) remain unchanged.

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Constant Pressure

Condition where pressure remains the same during the gas law experiment.

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Combined Gas Law

Relates pressure, volume, and temperature of a gas when conditions change.

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Combined Gas Law Equation

p1V1/T1 = p2V2/T2

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Gay-Lussac's Law of Combining Volumes

Gas volumes in reactions are in ratios of small whole numbers at same T & P.

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Avogadro’s Law

Equal volumes of gases, same T&P, have equal numbers of molecules.

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Molar Volume

Volume occupied by one mole of gas at specified temperature and pressure.

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STP Molar Volume

22.4 liters per mole at standard temperature and pressure.

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Room Temperature and Pressure (RTP) Molar Volume

24.0 liters per mole at room temperature and pressure.

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What is the purpose of the pinhole in the cap?

The pinhole allows the vapor inside the flask to equalize with atmospheric pressure, ensuring the pressure inside the flask matches the external pressure.

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Why do we heat the flask?

Heating vaporizes all the volatile liquid, allowing us to measure the mass of the vapor and then calculate the molar mass.

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What happens to the vapor as the flask cools?

As the flask cools, the vapor condenses back into a liquid, allowing us to determine the mass of the condensed liquid.

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How do we determine the volume of the vapor?

We completely fill the flask with water, measure the volume of the water, and since the vapor occupied the same space, we know its volume.

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Why is it important to dry the flask before measuring its final mass?

Any water droplets remaining on the outside of the flask will contribute to the mass, leading to an inaccurate measurement of the vapor's mass.

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What does the final mass difference tell us?

The difference between the initial and final mass represents the mass of the vapor that occupied the flask.

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What is the purpose of the barometer in this experiment?

The barometer measures atmospheric pressure, which is important because the pressure of the vapor inside the flask equals atmospheric pressure.

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Why do we need to know the temperature of the boiling water?

The temperature is crucial for calculating the molar mass of the volatile liquid using the ideal gas law.

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Kinetic Theory of Gases

A set of assumptions explaining gas behavior based on the constant movement and collisions of gas particles.

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Ideal Gas

A theoretical gas that perfectly obeys the Kinetic Theory of Gases under all conditions.

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Assumptions of the Kinetic Theory

  1. Gas particles are in constant motion, colliding with each other and container walls. 2. No attractive/repulsive forces between molecules. 3. Molecular volumes are negligible compared to the space between them. 4. Collisions are perfectly elastic (no energy loss). 5. Average particle kinetic energy depends on temperature (Kelvin scale).
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Elastic Collisions

Collisions between gas particles where no kinetic energy is lost, only transferred.

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Ideal Gas Law

An equation describing the relationship between pressure, volume, temperature, and the number of moles of an ideal gas: pV = nRT

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What are the limitations of the Kinetic Theory?

Real gases don't perfectly follow the assumptions of the Kinetic Theory. There are attractive forces between molecules and their volumes are not negligible, especially at high pressure and low temperature.

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Relative Molecular Mass (Volatile Liquid)

The mass of a molecule compared to the mass of a carbon-12 atom (relative to 12). This can be determined experimentally for volatile liquids by measuring their vapor pressure.

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Experiment Steps

  1. Heat water to near boiling. 2. Cover flask with foil, prick a hole. 3. Measure initial mass. 4. Add volatile liquid. 5. Seal tightly with foil, immerse in water. 6. Record final mass, temperature, pressure, and volume.
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Kinetic Theory of Gases Assumptions

  1. Gas particles are in constant, random, straight-line motion.
  2. The average kinetic energy of gas particles is directly proportional to the absolute temperature.
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Ideal Gas Behavior Deviations

Real gases deviate from ideal behavior due to:

  1. Intermolecular forces of attraction between gas particles.
  2. The volume of the gas particles themselves is not negligible.
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Moles of Gas Calculation

To calculate the number of moles of gas, you can use Avogadro's number: Number of Moles = (Number of Molecules) / Avogadro's Number

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Modern Technique for Molecular Mass Determination

Mass spectrometry is a modern instrumental technique that can accurately determine the relative molecular masses of various substances, including volatile and non-volatile liquids, solids, and gases.

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Study Notes

Gases

  • A gas is a substance without defined boundaries, quickly filling any container.
  • Gases are one of the three states of matter (solid, liquid, gas).

Gas Laws

Temperature

  • Measures the degree of hotness of an object.
  • Two scales used:
    • Kelvin (K): Absolute zero is -273°C.
    • Celsius (°C): Water freezes at 0°C and boils at 100°C.
  • Conversion: Add 273 to Celsius to get Kelvin

Pressure

  • Force exerted by a gas per unit area.
  • Measured in Newtons per square meter (N/m²), also known as pascals (Pa).
  • Standard atmospheric pressure: 1 x 10⁵ Pa or 100,000 Pa or 100kPa.
  • Common units include kPa (kilopascals) and hPa (hectopascals).

Volume

  • Same as the volume of the container holding the gas.
  • Measured in cubic meters (m³), cubic centimeters (cm³), or liters (L).
  • 1 litre = 1000 cm³ = 1 cubic decimeter (dm³)

Standard Temperature and Pressure (STP)

  • Standard temperature: 273 K
  • Standard pressure: 100,000 Pa

Boyle's Law

  • At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure.
  • pV = k (constant)
  • This means as pressure increases, volume decreases, and vice versa, if the temperature remains constant.
  • The graph of pressure versus inverse volume is a straight line through the origin.

Charles' Law

  • At constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature.
  • V/T = k (constant)
  • This means as temperature increases (in Kelvin), volume increases, and vice versa, if the pressure remains constant.
  • The graph of volume versus temperature is a straight line that does not pass through the origin; however, extending the line gives the x-intercept at -273°C.

Combined Gas Law

  • Combines Boyle's and Charles' laws into a single equation for relating pressure, volume, and temperature changes.
  • (P₁V₁)/T₁ = (P₂V₂)/T₂

Gay-Lussac's Law of Combining Volumes

  • In a reaction between gases, the volumes of reacting gases (and the products) are in a ratio of small whole numbers.
  • This only applies when the reaction is measured at the same temperature and pressure.

Avogadro's Law

  • Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.
  • At standard temperature and pressure (STP), one mole of any gas occupies 22.4 liters.

###Kinetic Theory of Gases

  • Gases consist of tiny particles in constant, random motion.
  • No forces of attraction or repulsion between the particles.
  • Particle volume is negligible compared to the space between them.
  • Collisions between particles are perfectly elastic.
  • The average kinetic energy is proportional to the Kelvin temperature.
  • Ideal gases perfectly follow these assumptions. Real gases deviate due to intermolecular forces and particle volumes.

Equation of State for an Ideal Gas

  • PV = nRT
    • P = pressure
    • V = volume
    • n = number of moles
    • R = ideal gas constant
    • T = absolute temperature (Kelvin)

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