Define thermal equilibrium .

When two substances in physical contact with each other no longer exchange heat energy and both reach an equal temperature .

What condition must be met for two substances to reach thermal equilibrium?

They must be in physical contact with each other.

Thermal energy is always transferred from a .......... region to a cooler region.

Thermal energy is always transferred from a hotter region to a cooler region.

As two regions of different temperature move towards thermal equilibrium, what happens to each region?

The hotter region cools down and the cooler region heats up until both reach the same temperature.

True or False? The final temperature reached at thermal equilibrium is always the same, regardless of the initial temperature difference between the two regions.

False. The final temperature at thermal equilibrium depends on the initial temperature difference between the two regions.

Define the thermodynamic (Kelvin) temperature scale .

An absolute temperature scale that is not defined in terms of a property of any particular substance.

What are the two fixed points on the absolute (thermodynamic) temperature scale?

The triple point of pure water and absolute zero .

What is the triple point of water ?

The point at which pure ice, pure water and pure water vapour all exist at the same temperature and pressure .

As well as Celsius, other temperature scales include Fahrenheit and .......... , which is used in thermodynamics.

As well as Celsius, other temperature scales include Fahrenheit and Kelvin , which is used in thermodynamics.

True or False? A temperature change of 1 K is equal to a temperature change of 2 °C.

False. The divisions on the Kelvin and Celsius scales are equal, so a change of 1 K is equal to a change of 1 °C .

Define the kinetic theory of matter .

A model that assumes particles are small solid spheres, used to explain the properties of the three states of matter.

Describe the arrangement and motion of particles in a solid .

Held together by strong intermolecular forces, closely packed in a fixed lattice pattern, and can only vibrate about their fixed positions.

Describe the arrangement and motion of particles in a liquid .

Held together by weaker intermolecular forces than in solids, closely packed , randomly arranged, and able to flow past each other.

Describe the arrangement and motion of particles in a gas .

Negligible intermolecular forces, far apart (around 10 times further apart than in solids or liquids), randomly arranged, and moving in all directions at a variety of speeds.

Gases do not have a fixed shape or .......... and expand to completely fill the available space.

Gases do not have a fixed shape or volume and expand to completely fill the available space.

True or False? Liquids are easier to compress than gases.

False. Liquids are difficult to compress as their particles are closely packed, whereas gases can be compressed since their particles are far apart.

Which state of matter has the highest density, and why?

Solids , because their particles are the most closely packed of the three states.

Define Brownian motion .

The random, erratic motion of small particles (such as pollen or smoke particles) suspended in a liquid or gas.

What does Brownian motion provide evidence for?

The existence of molecules in a gas or liquid.

In a smoke cell experiment, why are the much smaller air particles able to affect the motion of the larger smoke particles?

The air particles travel at a much higher speed than the smoke particles and have a lot of momentum , which they transfer to the smoke particles during collisions.

In Brownian motion, particles have a range of speeds and no preferred .......... of movement.

In Brownian motion, particles have a range of speeds and no preferred direction of movement.

True or False? In a smoke cell experiment, the particles observed moving under the microscope are the air molecules themselves.

False. The observed particles are the larger, heavier smoke particles , which are knocked about by the much smaller, faster-moving air molecules.

Define internal energy .

The sum of the randomly distributed kinetic and potential energies of atoms or molecules within a substance.

What two forms of energy make up the internal energy of a substance?

Kinetic energy (due to the speed and mass of the molecules) and electrostatic potential energy (due to the separation and forces of attraction between molecules).

State two ways the internal energy of a system can be increased.

By doing work on it, or by adding heat to it.

Define absolute zero .

0 K (−273.15 °C): the temperature at which the molecules in a substance have zero kinetic energy , so no more energy can be removed from the system.

How are internal energy and temperature related?

They are directly proportional : an increase in temperature causes a proportional increase in internal energy, and vice versa.

Temperature is a measure of the average .......... energy of the molecules in a substance.

Temperature is a measure of the average kinetic energy of the molecules in a substance.

While a substance is being heated during a phase change (e.g. liquid to gas), what happens to the kinetic and potential energy of its molecules?

Kinetic energy stays the same (so temperature stays constant), while electrostatic potential energy increases as bonds are broken and molecules move further apart.

True or False? A substance's temperature keeps changing throughout a phase change, even though it is being heated or cooled.

False. Temperature remains constant during a phase change, since the energy transferred changes the potential energy (breaking or forming bonds) rather than the kinetic energy.

Define specific heat capacity .

The amount of thermal energy required to raise the temperature of 1 kg of a substance by 1 °C.

What are the units of specific heat capacity?

J kg -1 K -1 (or J kg -1 °C -1 ).

How does a substance's specific heat capacity affect how quickly it heats up and cools down?

A low specific heat capacity means the substance heats up and cools down quickly ; a high specific heat capacity means it heats up and cools down slowly .

In the specific heat capacity experiment for a solid, after the power supply is switched off the .......... is monitored to record the highest temperature reached.

In the specific heat capacity experiment for a solid, after the power supply is switched off the thermometer is monitored to record the highest temperature reached.

In the specific heat capacity experiment, why is the calculated value of specific heat capacity often too high?

Not all the heat supplied by the heater goes into the substance; some heat is lost to the surroundings , making the value for energy supplied too large.

How can the effect of fluctuations in the power supply be reduced during the specific heat capacity experiment?

By taking several periodic measurements of voltage and current and calculating an average of these values.

True or False? Using better insulation around the apparatus in the specific heat capacity experiment would increase the measured value of specific heat capacity above the true value.

False. Better insulation reduces heat loss to the surroundings, giving a measured value closer to the true value , not a higher one.

Latent heat is the thermal energy required to change the state of 1 kg of a substance without any change in temperature.

Define specific latent heat of fusion .

The thermal energy required to convert 1 kg of solid to liquid with no change in temperature.

Define specific latent heat of vaporisation .

The thermal energy required to convert 1 kg of liquid to gas with no change in temperature.

During a change of state, a substance's .......... does not change.

During a change of state, a substance's temperature does not change.

True or False? A substance's temperature increases while it is melting.

False. Temperature stays constant during a change of state; the energy supplied increases molecular separation rather than temperature.

Why does vaporising 1 kg of water require roughly seven times more energy than melting 1 kg of ice?

Melting only increases molecular separation enough for molecules to flow over each other, whereas vaporising must completely separate the molecules until there are no intermolecular forces of attraction between them, requiring much more energy.

In the specific latent heat of fusion experiment, why is a second, unheated funnel and beaker of ice set up alongside the heated one?

It accounts for ice melted by heat transferred from the surroundings rather than the heater; the mass melted in the unheated beaker is subtracted from that in the heated beaker to find the mass melted due to the heater alone.

A LevelPhysicsOCRFlashcards5. Newtonian World & AstrophysicsThermal Properties of Materials

Thermal Properties of Materials (OCR A Level Physics): Flashcards

Exam code: H556

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FrontThermal Equilibrium
Define thermal equilibrium.

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Cards in this collection (49)

Define thermal equilibrium.
When two substances in physical contact with each other no longer exchange heat energy and both reach an equal temperature.
What condition must be met for two substances to reach thermal equilibrium?
They must be in physical contact with each other.
Thermal energy is always transferred from a .......... region to a cooler region.
Thermal energy is always transferred from a hotter region to a cooler region.
As two regions of different temperature move towards thermal equilibrium, what happens to each region?
The hotter region cools down and the cooler region heats up until both reach the same temperature.
True or False?
The final temperature reached at thermal equilibrium is always the same, regardless of the initial temperature difference between the two regions.
False.
The final temperature at thermal equilibrium depends on the initial temperature difference between the two regions.
Define the thermodynamic (Kelvin) temperature scale.
An absolute temperature scale that is not defined in terms of a property of any particular substance.
What are the two fixed points on the absolute (thermodynamic) temperature scale?
The triple point of pure water and absolute zero.
What is the triple point of water?
The point at which pure ice, pure water and pure water vapour all exist at the same temperature and pressure.
As well as Celsius, other temperature scales include Fahrenheit and .........., which is used in thermodynamics.
As well as Celsius, other temperature scales include Fahrenheit and Kelvin, which is used in thermodynamics.
State the equation used to convert a temperature θ in Celsius to a temperature T in Kelvin.
$T / K = θ /^{o} C + 273.15$
True or False?
A temperature change of 1 K is equal to a temperature change of 2 °C.
False.
The divisions on the Kelvin and Celsius scales are equal, so a change of 1 K is equal to a change of 1 °C.
What are the three states of matter?
Solid, liquid and gas.
Define the kinetic theory of matter.
A model that assumes particles are small solid spheres, used to explain the properties of the three states of matter.
Describe the arrangement and motion of particles in a solid.
Held together by strong intermolecular forces, closely packed in a fixed lattice pattern, and can only vibrate about their fixed positions.
Describe the arrangement and motion of particles in a liquid.
Held together by weaker intermolecular forces than in solids, closely packed, randomly arranged, and able to flow past each other.
Describe the arrangement and motion of particles in a gas.
Negligible intermolecular forces, far apart (around 10 times further apart than in solids or liquids), randomly arranged, and moving in all directions at a variety of speeds.
Gases do not have a fixed shape or .......... and expand to completely fill the available space.
Gases do not have a fixed shape or volume and expand to completely fill the available space.
True or False?
Liquids are easier to compress than gases.
False.
Liquids are difficult to compress as their particles are closely packed, whereas gases can be compressed since their particles are far apart.
Which state of matter has the highest density, and why?
Solids, because their particles are the most closely packed of the three states.
Define Brownian motion.
The random, erratic motion of small particles (such as pollen or smoke particles) suspended in a liquid or gas.
What does Brownian motion provide evidence for?
The existence of molecules in a gas or liquid.
In a smoke cell experiment, why are the much smaller air particles able to affect the motion of the larger smoke particles?
The air particles travel at a much higher speed than the smoke particles and have a lot of momentum, which they transfer to the smoke particles during collisions.
In Brownian motion, particles have a range of speeds and no preferred .......... of movement.
In Brownian motion, particles have a range of speeds and no preferred direction of movement.
True or False?
In a smoke cell experiment, the particles observed moving under the microscope are the air molecules themselves.
False.
The observed particles are the larger, heavier smoke particles, which are knocked about by the much smaller, faster-moving air molecules.
Define internal energy.
The sum of the randomly distributed kinetic and potential energies of atoms or molecules within a substance.
What two forms of energy make up the internal energy of a substance?
Kinetic energy (due to the speed and mass of the molecules) and electrostatic potential energy (due to the separation and forces of attraction between molecules).
State two ways the internal energy of a system can be increased.
By doing work on it, or by adding heat to it.
Define absolute zero.
0 K (−273.15 °C): the temperature at which the molecules in a substance have zero kinetic energy, so no more energy can be removed from the system.
How are internal energy and temperature related?
They are directly proportional: an increase in temperature causes a proportional increase in internal energy, and vice versa.
Temperature is a measure of the average .......... energy of the molecules in a substance.
Temperature is a measure of the average kinetic energy of the molecules in a substance.
While a substance is being heated during a phase change (e.g. liquid to gas), what happens to the kinetic and potential energy of its molecules?
Kinetic energy stays the same (so temperature stays constant), while electrostatic potential energy increases as bonds are broken and molecules move further apart.
True or False?
A substance's temperature keeps changing throughout a phase change, even though it is being heated or cooled.
False.
Temperature remains constant during a phase change, since the energy transferred changes the potential energy (breaking or forming bonds) rather than the kinetic energy.
Define specific heat capacity.
The amount of thermal energy required to raise the temperature of 1 kg of a substance by 1 °C.
What are the units of specific heat capacity?
J kg^-1 K^-1 (or J kg^-1 °C^-1).
How does a substance's specific heat capacity affect how quickly it heats up and cools down?
A low specific heat capacity means the substance heats up and cools down quickly; a high specific heat capacity means it heats up and cools down slowly.
State the equation linking thermal energy, mass, specific heat capacity and temperature change.
$E = m c Δ θ$
In the specific heat capacity experiment for a solid, after the power supply is switched off the .......... is monitored to record the highest temperature reached.
In the specific heat capacity experiment for a solid, after the power supply is switched off the thermometer is monitored to record the highest temperature reached.
In the specific heat capacity experiment, why is the calculated value of specific heat capacity often too high?
Not all the heat supplied by the heater goes into the substance; some heat is lost to the surroundings, making the value for energy supplied too large.
How can the effect of fluctuations in the power supply be reduced during the specific heat capacity experiment?
By taking several periodic measurements of voltage and current and calculating an average of these values.
True or False?
Using better insulation around the apparatus in the specific heat capacity experiment would increase the measured value of specific heat capacity above the true value.
False.
Better insulation reduces heat loss to the surroundings, giving a measured value closer to the true value, not a higher one.
Define latent heat.
Latent heat is the thermal energy required to change the state of 1 kg of a substance without any change in temperature.
Define specific latent heat of fusion.
The thermal energy required to convert 1 kg of solid to liquid with no change in temperature.
Define specific latent heat of vaporisation.
The thermal energy required to convert 1 kg of liquid to gas with no change in temperature.
During a change of state, a substance's .......... does not change.
During a change of state, a substance's temperature does not change.
State the equation linking thermal energy, mass and specific latent heat, and give the units of each quantity.
$E = m L$
E = thermal energy (J), m = mass changing state (kg), L = specific latent heat (J kg^-1).
True or False?
A substance's temperature increases while it is melting.
False.
Temperature stays constant during a change of state; the energy supplied increases molecular separation rather than temperature.
Why does vaporising 1 kg of water require roughly seven times more energy than melting 1 kg of ice?
Melting only increases molecular separation enough for molecules to flow over each other, whereas vaporising must completely separate the molecules until there are no intermolecular forces of attraction between them, requiring much more energy.
In the specific latent heat of fusion experiment, why is a second, unheated funnel and beaker of ice set up alongside the heated one?
It accounts for ice melted by heat transferred from the surroundings rather than the heater; the mass melted in the unheated beaker is subtracted from that in the heated beaker to find the mass melted due to the heater alone.
State the equation used to calculate the thermal energy supplied by the immersion heater in the specific latent heat experiments.
$energy = current \times potential difference \times time$

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