Define absolute zero .

Absolute zero is the lowest temperature possible, equal to 0 K or -273.15 °C It is the temperature at which the molecules in a substance have zero kinetic energy

True or False? A temperature in kelvin can be negative.

False. A temperature in kelvin can never be negative — 0 K (absolute zero) is the lowest possible temperature.

A change in temperature of one kelvin is equal to a change in temperature of ..........

A change in temperature of one kelvin is equal to a change in temperature of one degree Celsius

What is the approximate temperature of space?

Roughly 2.7 K , just above absolute zero.

Using the molecular model, explain why increasing the temperature of a gas at constant volume increases its pressure.

A higher temperature means the gas molecules move faster , so they collide with the container walls more frequently and with greater force . Since pressure is force per unit area, this increases the pressure.

How is pressure defined in terms of gas molecules?

Pressure is the frequency of collisions of the gas molecules per unit area of a container's walls.

For a fixed mass of gas, Boyle's law states that pressure is .......... proportional to volume at constant temperature.

For a fixed mass of gas, Boyle's law states that pressure is inversely proportional to volume at constant temperature.

True or False? A graph of volume against temperature in degrees Celsius, for a fixed mass of gas at constant pressure, passes through the origin.

False. The graph only passes through the origin when temperature is measured in kelvin . In degrees Celsius, the line crosses the temperature axis at -273 °C (absolute zero).

List the properties assumed of an ideal gas .

Molecules have negligible volume Collisions between molecules are elastic Cannot be liquified No interactions between molecules, except during collisions Obeys the ideal gas laws at any temperature or pressure

True or False? An ideal gas can be liquified if it is cooled to a low enough temperature.

False. By definition, an ideal gas cannot be liquified, at any temperature or pressure.

What unit must temperature be in when using the ideal gas equation?

Kelvin (K) — the thermodynamic temperature scale.

State whether work is done by or on a gas when it expands , and when it is compressed .

When a gas expands (volume increases), work is done by the gas When a gas is compressed (volume decreases), work is done on the gas

The equation W = p Δ V assumes that the .......... of the gas does not change as it expands.

The equation W = p Δ V assumes that the pressure of the gas does not change as it expands.

True or False? When a gas is compressed, Δ V in the equation W = p Δ V is positive.

False. Δ V = final volume − initial volume, so when a gas is compressed (volume decreases), Δ V is negative , meaning work is done on the gas.

In a cylinder enclosed by a moveable piston, how does an expanding gas do work?

The expanding gas exerts a force on the piston, pushing it outward through a distance — the gas does work on the piston .

Define Avogadro's constant .

The number of atoms of carbon-12 in 12 g of carbon-12; equal to 6.02 × 10 23 mol -1

The mass, in grams, of one mole of a substance. Its unit is g mol -1

One mole of any element is equal to the .......... of that element in grams.

One mole of any element is equal to the relative atomic mass of that element in grams.

What is the mass of the atomic mass unit, u ?

1.66 × 10 -27 kg , approximately the mass of a proton or neutron.

True or False? One mole of helium contains 6.02 × 10 23 grams of helium.

False. One mole of helium contains 6.02 × 10 23 atoms of helium, not grams. The mass of one mole of helium is 4 g (its relative atomic mass).

In the Boyle's law investigation, what are the independent and dependent variables?

Independent variable: mass, m (kg) Dependent variable: volume, V (m 3 )

In the Boyle's law investigation, what variables must be controlled?

Temperature Cross-sectional area of the syringe

What graph is plotted to confirm Boyle's law, and what result confirms it?

A graph of pressure p against 1 / V is plotted. A straight line through the origin confirms p is proportional to 1 / V (i.e. pV = constant)

What is the main systematic error in the Boyle's law investigation, and how can it be reduced?

Friction in the syringe. Use a syringe with very little friction, or lubricate it, so the only force applied is from the masses.

In the Charles's law investigation, what are the independent and dependent variables?

Independent variable: temperature, T (°C) Dependent variable: height of the gas column, h (cm)

In the Charles's law investigation, a drop of .......... is added to the capillary tube to trap the gas column and stop it escaping.

In the Charles's law investigation, a drop of sulfuric acid is added to the capillary tube to trap the gas column and stop it escaping.

True or False? In the Boyle's law investigation, the pressure of the gas is equal to the pressure exerted by the added masses.

False. The pressure of the gas equals atmospheric pressure minus the pressure exerted by the masses, not the exerted pressure alone.

A LevelPhysicsAQAFlashcardsFurther Mechanics & Thermal PhysicsIdeal Gases

Ideal Gases (AQA A Level Physics): Flashcards

Exam code: 7408

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FrontThe Kelvin Scale & Absolute Zero
Define absolute zero.
BackThe Kelvin Scale & Absolute Zero
Absolute zero is the lowest temperature possible, equal to 0 K or -273.15 °C
It is the temperature at which the molecules in a substance have zero kinetic energy
BackThe Kelvin Scale & Absolute Zero
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Cards in this collection (40)

Define absolute zero.
- Absolute zero is the lowest temperature possible, equal to 0 K or -273.15 °C
- It is the temperature at which the molecules in a substance have zero kinetic energy
What is the equation used to convert a temperature θ in degrees Celsius to a temperature T in kelvin?
$T / K = θ / ° C + 273.15$
True or False?
A temperature in kelvin can be negative.
False.
A temperature in kelvin can never be negative — 0 K (absolute zero) is the lowest possible temperature.
A change in temperature of one kelvin is equal to a change in temperature of ..........
A change in temperature of one kelvin is equal to a change in temperature of one degree Celsius
Why is it not necessary to convert Δθ between degrees Celsius and kelvin when using $Q = m c Δ θ$ ?
Because the divisions on the kelvin and Celsius scales are equal in size, a temperature difference is exactly the same whether measured in kelvin or in degrees Celsius.
What is the approximate temperature of space?
Roughly 2.7 K, just above absolute zero.
Define Boyle's law.
For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume:
$p_{1} V_{1} = p_{2} V_{2}$
Define Charles's law.
For a fixed mass of gas at constant pressure, volume is directly proportional to thermodynamic temperature:
$\frac{V_{1}}{T_{1}} = \frac{V_{2}}{T_{2}}$
Define the pressure law.
For a fixed mass of gas at constant volume, pressure is directly proportional to thermodynamic temperature:
$\frac{p_{1}}{T_{1}} = \frac{p_{2}}{T_{2}}$
Using the molecular model, explain why increasing the temperature of a gas at constant volume increases its pressure.
A higher temperature means the gas molecules move faster, so they collide with the container walls more frequently and with greater force. Since pressure is force per unit area, this increases the pressure.
How is pressure defined in terms of gas molecules?
Pressure is the frequency of collisions of the gas molecules per unit area of a container's walls.
For a fixed mass of gas, Boyle's law states that pressure is .......... proportional to volume at constant temperature.
For a fixed mass of gas, Boyle's law states that pressure is inversely proportional to volume at constant temperature.
True or False?
A graph of volume against temperature in degrees Celsius, for a fixed mass of gas at constant pressure, passes through the origin.
False.
The graph only passes through the origin when temperature is measured in kelvin. In degrees Celsius, the line crosses the temperature axis at -273 °C (absolute zero).
Define an ideal gas.
A gas which obeys the equation of state $p V = n R T$ at all pressures, volumes and temperatures.
List the properties assumed of an ideal gas.
- Molecules have negligible volume
- Collisions between molecules are elastic
- Cannot be liquified
- No interactions between molecules, except during collisions
- Obeys the ideal gas laws at any temperature or pressure
What does each term represent in the ideal gas equation $p V = n R T$ ?
- p = pressure (Pa)
- V = volume (m³)
- n = number of moles (mol)
- R = molar gas constant
- T = thermodynamic temperature (K)
The ideal gas equation can also be written as $p V =$ .........., where N is the number of molecules and k is the Boltzmann constant.
The ideal gas equation can also be written as $p V = N k T$ , where N is the number of molecules and k is the Boltzmann constant.
True or False?
An ideal gas can be liquified if it is cooled to a low enough temperature.
False.
By definition, an ideal gas cannot be liquified, at any temperature or pressure.
What unit must temperature be in when using the ideal gas equation?
Kelvin (K) — the thermodynamic temperature scale.
Define the work done by a gas.
The work done when a volume of gas changes at constant pressure:
$W = p Δ V$
- W = work done (J)
- p = pressure of the gas (Pa)
- ΔV = change in volume of the gas (m³)
State whether work is done by or on a gas when it expands, and when it is compressed.
- When a gas expands (volume increases), work is done by the gas
- When a gas is compressed (volume decreases), work is done on the gas
The equation W = pΔV assumes that the .......... of the gas does not change as it expands.
The equation W = pΔV assumes that the pressure of the gas does not change as it expands.
True or False?
When a gas is compressed, ΔV in the equation W = pΔV is positive.
False.
ΔV = final volume − initial volume, so when a gas is compressed (volume decreases), ΔV is negative, meaning work is done on the gas.
In a cylinder enclosed by a moveable piston, how does an expanding gas do work?
The expanding gas exerts a force on the piston, pushing it outward through a distance — the gas does work on the piston.
Define Avogadro's constant.
The number of atoms of carbon-12 in 12 g of carbon-12; equal to 6.02 × 10²³ mol^-1
Define molar mass.
The mass, in grams, of one mole of a substance. Its unit is g mol^-1
How is the number of moles of a substance calculated from its mass?
$n = \frac{mass}{molar mass}$
Define the Boltzmann constant.
$k = \frac{R}{N_{A}}$
where R = molar gas constant and N_A = Avogadro's constant. It has a value of 1.38 × 10^-23 J K^-1, and relates the microscopic properties of particles (e.g. kinetic energy) to their macroscopic properties (e.g. temperature)
One mole of any element is equal to the .......... of that element in grams.
One mole of any element is equal to the relative atomic mass of that element in grams.
What is the mass of the atomic mass unit, u?
1.66 × 10^-27 kg, approximately the mass of a proton or neutron.
True or False?
One mole of helium contains 6.02 × 10²³ grams of helium.
False.
One mole of helium contains 6.02 × 10²³ atoms of helium, not grams. The mass of one mole of helium is 4 g (its relative atomic mass).
In the Boyle's law investigation, what are the independent and dependent variables?
- Independent variable: mass, m (kg)
- Dependent variable: volume, V (m³)
In the Boyle's law investigation, what variables must be controlled?
- Temperature
- Cross-sectional area of the syringe
How is the pressure of the gas calculated in the Boyle's law investigation?
$Pressure of gas = Atmospheric pressure - Exerted pressure from the masses$
What graph is plotted to confirm Boyle's law, and what result confirms it?
A graph of pressure p against 1 / V is plotted. A straight line through the origin confirms p is proportional to 1 / V (i.e. pV = constant)
What is the main systematic error in the Boyle's law investigation, and how can it be reduced?
Friction in the syringe. Use a syringe with very little friction, or lubricate it, so the only force applied is from the masses.
In the Charles's law investigation, what are the independent and dependent variables?
- Independent variable: temperature, T (°C)
- Dependent variable: height of the gas column, h (cm)
How is the value of absolute zero determined from the Charles's law investigation graph?
Plot height h against temperature T and find the gradient m, then use:
$T_{0} = T_{1} - \frac{h_{1}}{m}$
where (T₁, h₁) is any point on the line of best fit and h₀ = 0 at absolute zero
In the Charles's law investigation, a drop of .......... is added to the capillary tube to trap the gas column and stop it escaping.
In the Charles's law investigation, a drop of sulfuric acid is added to the capillary tube to trap the gas column and stop it escaping.
True or False?
In the Boyle's law investigation, the pressure of the gas is equal to the pressure exerted by the added masses.
False.
The pressure of the gas equals atmospheric pressure minus the pressure exerted by the masses, not the exerted pressure alone.

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