14: Simple Models of Matter Flashcards

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1
Q

Where is thermal energy always transferred?

A

From regions of higher temperature to regions of lower temperature

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2
Q

A change in temperature shows thermal energy has been [ ]

A

Transferred

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3
Q

What does a net transfer of thermal energy cause?

A

A change in temperature

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4
Q

What is specific thermal capacity?

A

The amount of energy needed to raise the temperature of 1 kg of the substance by 1K

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5
Q

What is the set up to measure specific thermal capacity of a solid?

A

Put a digital thermometer in a hole in your solid
Surround your solid with insulating material
Put an electric heater in another hole in your solid

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6
Q

What is the set up for liquids, in order to find the specific thermal capacity?

A

Have a heating coil inside a beaker of your liquid with a digital thermometer in the beaker surrounded by insulating material and an insulating lid

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7
Q

Why is the value you get for specific thermal capacity usually too high in experiments? How can you improve this?

A

Some of the energy from the heater will get transferred to the air and the container. To minimise this affect, start below and finish above room temperature to cancel out gains and losses. Some energy will also be lost due to resistance in the circuit

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8
Q

Describe the experiment to find specific thermal capacity

A

Heat the substance with the heater so that its temperature increases by about 10 K
Attach an ammeter and voltmeter to your electric heater. You can then calculate the work done by the heater
If you assume all of the work done by the heat is transferred into thermal energy energy in the solid or liquid, you can then plug your data into E = mcΔθ

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9
Q

What is an ideal gas?

A

A model, based on a set of assumptions
An ideal gas is a good approximation of a real gas as long as the pressure isn’t too great and the temperature is reasonably high, compared with the gas’s boiling point

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10
Q

What does Boyle’s Law state?

A

At a constant temperature, the pressure p and the volume V of a gas are inversely proportional

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11
Q

Do ideal gases always obey the three gas laws?

A

Yes

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12
Q

Describe what difference temperature makes to a line on the pressure volume graph

A

The higher the temperature of the gas, the further the curve is from the origin

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13
Q

How can you investigate the effects of pressure on volume?

A

The oil confines a parcel of air in a sealed tube with fixed dimensions. A tyre pump is used to increase the pressure in the tube and the Bourdon gauge records the pressure. As the pressure increases the air will compress on the volume occupied by air in the tube will reduce.
Measure the volume of air when the system is that atmospheric pressure, then gradually increase the pressure, noting down both the pressure and the volume of air. Multiplying them together at any point you should give a constant

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14
Q

What does Charles’ law state?

A

At constant pressure, the volume of the gas is directly proportional to its absolute temperature

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15
Q

What does the graph of pressure against temperature look like for an ideal gas?

A

A straight line, intersecting the X axis at -273.15 Celsius, with a positive gradient

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16
Q

Describe the set up for the investigation of the pressure law

A

Put a flask with a stopper on the top and a beaker of water with a thermometer also in the beaker. The stopper in the top of the flask should be connected by tube to a Bourdon gauge
The volume of the tubing must be much smaller than the volume of the flask.
Make sure as much of the flask is submerged as possible

17
Q

Describe the investigation of the pressure law

A

Record the temperature of the water and the pressure on the gauge.
Heat the water for a few minutes then remove the heat source, stir the water to ensure it is at her uniform temperature and allow some time for the heat to be transferred from the water to the air. Record the pressure on the gauge and the temperature, then heat the water again and repeat until the water boils. Repeat your experiment twice more with fresh cold water, taking pressure measurements at the same set of temperatures each time.
Plot your results on a graph of pressure against temperature. Draw a line of best fit.

18
Q

What else can you find in the investigation of the pressure law?

A

This experiment also allows you to estimate the value of absolute zero, again by extrapolating your line of best fit until it reaches the x-axis

19
Q

What equation do you get if you combine all three gas laws?

A

pV/T = constant

20
Q

What conditions must be met, for a gas to obey as an ideal gas?

A

Low-pressure and fairly high temperatures

21
Q

What is R, in gas equations? k?

A

R is the gas constant for one mole of gas

k is the gas constant for one gas particle

22
Q

What are some simplifying assumptions that are used in kinetic theory?

A

Particles occupy a negligible volume compared with the volume of the container
Collisions between particles themselves or at the walls of the container are perfectly elastic, so no energy is lost.
There are negligible forces between particles, except when they collide.
The gas contains a large number of particles to move rapidly and randomly and that the motion of the particle obeys Newton’s laws

23
Q

What do you use to model the movement of the gas particle?

A

Random walk

24
Q

What does a random walk assume?

A

Each particle starts in one place, moves N steps in random directions, and ends up somewhere else

25
Q

What is diffusion?

A

The net movement of particles from an area of higher concentration to an area of low concentration

26
Q

Why does it take a long time for gases to diffuse?

A

The distance of particle can travel between collisions is usually around 10⁻⁷ m. So to travel 1 m from a starting point, a particle will have had to take 10 million steps.

27
Q

What is Newton’s second law in relation to gas particles?

A

The force exerted by a particle in a collision is equal to the rate of change of momentum of the particle

28
Q

What does newtons second law mean about the force exerted on the wall depending on the speed of the particle?

A

If a particle collides with a wall of the container, the faster it is travelling, the more force it exerts on the wall

29
Q

What is the area under the force time graph equal to?

A

The change in the momentum, or the impulse of the interaction

30
Q

Explain root mean square speed

A

As the particles in a gas are moving in different directions, if you averaged their velocities you’d get zero
Instead, you take the average of the squared velocities. This quantity is called the mean square speed
The square root of this number gives you the speed of a typical particle, the root mean square speed

31
Q

Explain the basis of understanding of an ideal gas, by thinking about the gas particle in a box
(Deriving the different gas equation)

A

A cubic box with sides of length, l, containing one particle, Q, of mass, m.
Say particle Q moves horizontally towards the wall A with a velocity u, so it’s momentum is mu. It strikes wall A, exerting a force on the wall, and heads back in the opposite direction

32
Q

State the four main facts, that are used to derive the different gas equation

A

1) Particle velocity is proportional to the pressure
2) The number of particles, N, is proportional to the pressure
3) The volume of the box is inversely proportional to the pressure
4) Particles travel in random directions at different velocities

33
Q

Explain why the pressure will be greater in a box, if the particle travels faster
(Deriving the different gas equation)

A

The faster the particles, the larger its momentum, so the greater the impulse of the collision and the larger the force on the wall. The particle will also take less time to travel across the box and back again, and so will hit the walls more often. And as pressure = force/area, the pressure will be greater to

34
Q

Why is the number of particles proportional to the pressure?

Deriving the different gas equation

A

Imagine you’ve got a whole stream of particles hitting wall A. Each particle exerts a force on the wall as it hits it, so the total force on the wall will be proportional to the number of particles. Pressure = force/area, the pressure is proportional to the number of particles too

35
Q

Explain why the volume of the box is inversely proportional to the pressure
(Deriving the different gas equation)

A

Imagine you shrink the box. The particles have less distance to travel before they hit a wall, so you’ve increased the number of times the particles hit the walls of the box per second, which increases the total force on the wall. Because the box is now smaller, the area of the wall is smaller. So there is a greater force on a smaller area, meaning the pressure is greater

36
Q

Explain what the consequence of particles travelling in random directions at different velocities
(Deriving the different gas equation)

A

You can estimate that a third of all the particles are travelling in one dimension at any time, as there are three dimensions. To take account of the different particle velocities, you can use the mean square speed.

37
Q

What is the internal energy of a system equal to?

A

The sum of the kinetic and potential energy of the particles within a system

38
Q

What is all the internal energy of an ideal gas due to? Why?

A

Due to the kinetic energy of its particles, there is no potential energy

39
Q

Describe the relationship between internal energy and temperature of an ideal gas. Explain why

A

Internal energy of an ideal gas is proportional to its absolute temperature.
A rise an absolute temperature increases the kinetic energy of each particle, causing a rise in internal energy