Define random motion .

Random motion is motion in which molecules travel in no specific path, undergoing sudden changes in direction when they collide with the walls of their container or with other molecules.

Define Brownian motion .

Brownian motion is the random motion of tiny particles (such as smoke or pollen particles) in a fluid, caused by collisions with smaller, invisible molecules.

What evidence does Brownian motion provide about the nature of air?

It provides evidence that air is made up of small, moving particles, since larger particles (such as smoke or pollen) are observed moving randomly due to collisions with smaller particles that are invisible to the naked eye.

Explain how collisions between gas molecules and the walls of a container produce pressure .

As gas molecules move randomly, they collide with the walls of the container. These collisions produce a net force at right angles to the wall, and this force acting per unit area is the pressure.

True or False? A gas at high pressure has less frequent collisions with its container walls than a gas at low pressure.

False. A gas at high pressure has more frequent collisions with the container walls, producing a greater force per unit area.

Molecules in a gas are in constant ______ motion at high speeds.

Molecules in a gas are in constant random motion at high speeds.

Define absolute zero .

Absolute zero is the temperature at which the molecules in a substance have zero kinetic energy. It is equal to −273 °C (0 K), and it is not possible to have a lower temperature.

Why does the pressure of a gas fall as its temperature decreases towards absolute zero ?

As temperature decreases, the gas particles move with less energy. At absolute zero the particles are no longer moving, so they no longer collide with the container walls, and the gas exerts no pressure.

Approximately how far above absolute zero is the temperature of space?

Space is roughly 2.7 K above absolute zero.

Define the Kelvin scale .

The Kelvin scale is a temperature scale that begins at absolute zero (0 K = −273 °C), where a change of 1 K is equal to a change of 1 °C.

A temperature of 0 °C is equal to ______ K.

A temperature of 0 °C is equal to 273 K.

True or False? It is possible for a temperature in kelvin to be negative.

False. The Kelvin scale begins at absolute zero (0 K), so a temperature in kelvin can never be negative.

Define temperature (in the kinetic theory of gases).

Temperature is a measure of the average speed of the molecules in a substance; the higher the temperature, the faster the molecules move, on average.

Define internal energy of a gas.

For a gas, internal energy is the sum of the kinetic energies of all its molecules. Since intermolecular forces in a gas are negligible, the potential energy contribution can be taken as zero.

At constant volume, how does an increase in temperature affect the kinetic energy and pressure of a gas?

An increase in temperature makes the molecules move faster, so they gain kinetic energy and collide with the container walls more often, increasing the pressure .

The relationship between temperature and average kinetic energy applies to ______ states of matter, although particle motion differs between them.

The relationship between temperature and average kinetic energy applies to all states of matter, although particle motion differs between them.

True or False? When a liquid evaporates, the temperature of the liquid decreases.

True. The most energetic molecules escape from the surface during evaporation, lowering the average kinetic energy of the remaining molecules, so the temperature of the liquid decreases.

At constant temperature, what happens to the pressure of a fixed mass of gas when it is compressed ?

The volume decreases, so the gas molecules collide with the container walls more frequently over a smaller area, creating a greater net force per unit area, so the pressure increases .

At constant temperature, what happens to the pressure of a fixed mass of gas when it is expanded ?

The volume increases, so the molecules collide with the container walls less frequently, so the pressure decreases .

At constant volume, how and why does an increase in temperature affect the pressure of a gas?

An increase in temperature increases the average speed and kinetic energy of the molecules. They collide with the container walls more often, so the pressure increases .

A vacuum pump is a device used to remove air (gas) from a sealed container, decreasing the pressure inside it.

When a gas is compressed at constant temperature, the molecules collide with the container walls ______ frequently, increasing the pressure.

When a gas is compressed at constant temperature, the molecules collide with the container walls more frequently, increasing the pressure.

True or False? At constant volume, increasing the temperature of a gas decreases its pressure.

False. At constant volume, increasing the temperature increases the pressure, since molecules move faster and collide with the walls more often.

In the pressure law equation, which temperature scale must be used, and why?

Temperature T must be in kelvin (K) . The pressure law depends on direct proportionality with kelvin temperature, which starts at absolute zero; using degrees Celsius would give an incorrect ratio.

According to the pressure law, if the kelvin temperature of a fixed mass of gas at constant volume doubles, its pressure will ______ .

According to the pressure law, if the kelvin temperature of a fixed mass of gas at constant volume doubles, its pressure will double .

True or False? The pressure law applies to a fixed mass of gas whose volume is changing.

False. The pressure law applies when the volume is constant ; only the pressure and kelvin temperature change.

Why does compressing a gas at constant temperature increase its pressure?

When the volume decreases, the same number of particles collide with the container walls more frequently in the smaller space. Since each collision still exerts the same force, the force per unit area ( pressure ) increases.

According to Boyle's law, pressure and volume are ______ proportional to each other.

According to Boyle's law, pressure and volume are inversely proportional to each other.

True or False? For Boyle's law to apply, the mass and temperature of the gas must stay the same.

True. Boyle's law assumes a fixed mass of gas at constant temperature; only the pressure and volume change.

IGCSEPhysicsEdexcelPhysics (Modular)Unit 2Flashcards6. Solids, Liquids & Gases: Part 2Ideal Gases

Ideal Gases (Edexcel IGCSE Physics (Modular): Unit 2): Flashcards

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Cards in this collection (38)

Define random motion.
Random motion is motion in which molecules travel in no specific path, undergoing sudden changes in direction when they collide with the walls of their container or with other molecules.
Define Brownian motion.
Brownian motion is the random motion of tiny particles (such as smoke or pollen particles) in a fluid, caused by collisions with smaller, invisible molecules.
Define pressure.
Pressure is the force per unit area:
$p = \frac{F}{A}$
Where p = pressure (Pa), F = force (N), A = area (m²).
What evidence does Brownian motion provide about the nature of air?
It provides evidence that air is made up of small, moving particles, since larger particles (such as smoke or pollen) are observed moving randomly due to collisions with smaller particles that are invisible to the naked eye.
Explain how collisions between gas molecules and the walls of a container produce pressure.
As gas molecules move randomly, they collide with the walls of the container. These collisions produce a net force at right angles to the wall, and this force acting per unit area is the pressure.
True or False?
A gas at high pressure has less frequent collisions with its container walls than a gas at low pressure.
False.
A gas at high pressure has more frequent collisions with the container walls, producing a greater force per unit area.
Molecules in a gas are in constant ______ motion at high speeds.
Molecules in a gas are in constant random motion at high speeds.
Define absolute zero.
Absolute zero is the temperature at which the molecules in a substance have zero kinetic energy. It is equal to −273 °C (0 K), and it is not possible to have a lower temperature.
Why does the pressure of a gas fall as its temperature decreases towards absolute zero?
As temperature decreases, the gas particles move with less energy. At absolute zero the particles are no longer moving, so they no longer collide with the container walls, and the gas exerts no pressure.
Approximately how far above absolute zero is the temperature of space?
Space is roughly 2.7 K above absolute zero.
Define the Kelvin scale.
The Kelvin scale is a temperature scale that begins at absolute zero (0 K = −273 °C), where a change of 1 K is equal to a change of 1 °C.
What equation converts a temperature θ in °C to a temperature T in K?
$T / K = θ / ° C + 273$
Where θ = temperature in degrees Celsius (°C), T = temperature in kelvin (K).
A temperature of 0 °C is equal to ______ K.
A temperature of 0 °C is equal to 273 K.
True or False?
It is possible for a temperature in kelvin to be negative.
False.
The Kelvin scale begins at absolute zero (0 K), so a temperature in kelvin can never be negative.
Define temperature (in the kinetic theory of gases).
Temperature is a measure of the average speed of the molecules in a substance; the higher the temperature, the faster the molecules move, on average.
Define internal energy of a gas.
For a gas, internal energy is the sum of the kinetic energies of all its molecules. Since intermolecular forces in a gas are negligible, the potential energy contribution can be taken as zero.
At constant volume, how does an increase in temperature affect the kinetic energy and pressure of a gas?
An increase in temperature makes the molecules move faster, so they gain kinetic energy and collide with the container walls more often, increasing the pressure.
How is the temperature (in kelvin) of a gas related to the average kinetic energy of its molecules?
$T \propto K E$
Temperature in kelvin, T, is directly proportional to the average kinetic energy, KE, of the molecules.
The relationship between temperature and average kinetic energy applies to ______ states of matter, although particle motion differs between them.
The relationship between temperature and average kinetic energy applies to all states of matter, although particle motion differs between them.
True or False?
When a liquid evaporates, the temperature of the liquid decreases.
True.
The most energetic molecules escape from the surface during evaporation, lowering the average kinetic energy of the remaining molecules, so the temperature of the liquid decreases.
At constant temperature, what happens to the pressure of a fixed mass of gas when it is compressed?
The volume decreases, so the gas molecules collide with the container walls more frequently over a smaller area, creating a greater net force per unit area, so the pressure increases.
At constant temperature, what happens to the pressure of a fixed mass of gas when it is expanded?
The volume increases, so the molecules collide with the container walls less frequently, so the pressure decreases.
At constant volume, how and why does an increase in temperature affect the pressure of a gas?
An increase in temperature increases the average speed and kinetic energy of the molecules. They collide with the container walls more often, so the pressure increases.
Define vacuum pump.
A vacuum pump is a device used to remove air (gas) from a sealed container, decreasing the pressure inside it.
When a gas is compressed at constant temperature, the molecules collide with the container walls ______ frequently, increasing the pressure.
When a gas is compressed at constant temperature, the molecules collide with the container walls more frequently, increasing the pressure.
True or False?
At constant volume, increasing the temperature of a gas decreases its pressure.
False.
At constant volume, increasing the temperature increases the pressure, since molecules move faster and collide with the walls more often.
Define the pressure law.
The pressure law states that for a fixed mass of gas at constant volume, the pressure is directly proportional to the kelvin temperature:
$P \propto T$
Where P = pressure (Pa), T = temperature (K).
Write the equation relating the initial and final pressure and temperature of a fixed mass of gas at constant volume.
$\frac{p_{1}}{T_{1}} = \frac{p_{2}}{T_{2}}$
Where p₁ = initial pressure (Pa), T₁ = initial temperature (K), p₂ = final pressure (Pa), T₂ = final temperature (K).
In the pressure law equation, which temperature scale must be used, and why?
Temperature T must be in kelvin (K). The pressure law depends on direct proportionality with kelvin temperature, which starts at absolute zero; using degrees Celsius would give an incorrect ratio.
According to the pressure law, if the kelvin temperature of a fixed mass of gas at constant volume doubles, its pressure will ______.
According to the pressure law, if the kelvin temperature of a fixed mass of gas at constant volume doubles, its pressure will double.
True or False?
The pressure law applies to a fixed mass of gas whose volume is changing.
False.
The pressure law applies when the volume is constant; only the pressure and kelvin temperature change.
The air in a bicycle tyre is at 5.10 × 10⁵ Pa when the temperature is 279 K. If the volume is unchanged and the temperature rises to 299 K, what is the new pressure?
$p_{2} = \frac{p_{1}}{T_{1}} \times T_{2} = \frac{5.10 \times 10^{5}}{279} \times 299 = 5.47 \times 10^{5} Pa$
Define Boyle's law.
Boyle's law states that for a fixed mass of gas at constant temperature, the product of pressure and volume is constant:
$p V = constant$
Where p = pressure (Pa), V = volume (m³).
Write the equation relating the initial and final pressure and volume of a fixed mass of gas at constant temperature.
$p_{1} V_{1} = p_{2} V_{2}$
Where p₁ = initial pressure (Pa), V₁ = initial volume (m³), p₂ = final pressure (Pa), V₂ = final volume (m³).
Why does compressing a gas at constant temperature increase its pressure?
When the volume decreases, the same number of particles collide with the container walls more frequently in the smaller space. Since each collision still exerts the same force, the force per unit area (pressure) increases.
According to Boyle's law, pressure and volume are ______ proportional to each other.
According to Boyle's law, pressure and volume are inversely proportional to each other.
True or False?
For Boyle's law to apply, the mass and temperature of the gas must stay the same.
True.
Boyle's law assumes a fixed mass of gas at constant temperature; only the pressure and volume change.
A gas occupies 0.70 m³ at a pressure of 200 Pa. Calculate the pressure when it is compressed to 0.15 m³ at constant temperature and mass.
$p_{2} = \frac{p_{1} V_{1}}{V_{2}} = \frac{200 \times 0.70}{0.15} = 930 Pa (2 s.f.)$

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