Tempreture, Ideal Gas, & Thermodynamics

Question 1

Describe the basic principle by which tempreture is measured.

Answer 1

It uses a property of a substance that changes with tempreture.

Question 2

Explain what is meant by the statement that two bodies are in thermal equilibrium.

Answer 2

No net enrgy transfer between bodies.
or
Bodies are at the same tempreture.

Question 3

Define specific heat capacity.

Answer 3

Energy required per unit mass to raise the temperature of a substance
by one degree.

Question 4

State what is meant by specific latent heat.

Answer 4

Energy required to change the state of a substance per unit mass without any change of tempreture.

Question 5

Define specific latent heat of fusion.

Answer 5

Energy required to change the state of a unit mass from solid to liquid without any change of tempreture

Question 6

Define specific latent heat of vaporization.

Answer 6

Energy required to change the state of a unit mass from liquid to solid without any changes of tempreture.

Question 7

The Latent Heat of Vaporization is much greater than the Latent Heat of Fusion. Explain this, in terms of the spacing of molecules.

Answer 7

Spacing of molecules has a greater increase for vaporization compared to fusion.

Question 8

Explain why, although the power of the heater is changed, the rate of loss of thermal energy to the surroundings may be assumed to be constant.

Answer 8

Tempreture difference between liquid and surroundings does not change.

Question 9

State what is observed by the student that shows that the ice is melting at a constant rate.

Answer 9

1. Constant time between drops
2. Constant rate of dripping
3. Volume of water increases at a constant rate
4. Rate of increase in mass is constant

Question 10

During melting, a solid becomes liquid with little or no change in volume.

Use Kinetic theory to explain why during the melting process, thermal energy is required although there is no change in tempreture.

Answer 10

During melting, bonds between molecules are broken, so the potential energy of the molecules increases, no change in volume means no work done and so required input of energy is thermal.

Question 11

Define the avagadro’s constant.

Answer 11

Number of atoms in 12 grams of carbon-12

Question 12

Define the mole.

Answer 12

The amount of substance which contains the same number of atoms as there are atoms in 12 grams of carbon-12

Question 13

State what is meant by an ideal gas.

Answer 13

A gas which obeys the law: PV/T=Constant where P is pressure, V is volume, and T is thermodynamic tempreture.

Question 14

In the equation pV/T = Nk

State the meaning of both the ‘N’ and ‘k’

Answer 14

N: Number of molecules
k: Boltzmann constant

Question 15

For pV=1/3Nm< c^2 >

State the meaning of the symbols “N” and “< c^2 >”

Answer 15

1. N, number of gas molecules
2. < c^2 >, mean square speed

Question 16

State the assumptions of the kinetic theory of gases.

Answer 16

1. Molecules move in random motion
2. Molecules have negligible volume
   (compared with the gas/container)
3. No forces between molecules (except during collisions)

Question 17

Describe the motion of molecules in a gas, according to the kinetic theory of gases.

Answer 17

1. Random
2. Constant Velocity

Question 18

State what is meant by an elastic collision.

Answer 18

No loss of kinetic energy.

Question 19

Explain how movement of the gas molecules causes pressure in the container.

Answer 19

1. Molecules collide with wall
2. Momentum of molecule changes during collision
3. Forces are exerted on wall and act over surface area of container exerting a pressure

Question 20

State what is meant by the internal energy of a system.

Answer 20

The sum of the random motion of kinetic and potential energy of molecules

Question 21

Explain why the change in internal energy of an ideal gas is equal to the change in total kinetic energy of its molecules.

Answer 21

Internal energy is the sum of kinetic and potential energies of a molecule, however in an ideal gas the potential energy of molecules is zero and so the change in internal energy would be equal to the total kinetic energy only.

Question 22

The first law of thermodynamics may be expressed as:

^U = (+q) + (+w)

State the meaning of each symbol.

Answer 22

^U: Increase in internal energy

+Q: thermal energy transferred to system

+W: work done on the system

Question 23

State what is represented by a negative value of ^U.

Answer 23

The decrease in internal energy.

Question 24

Using a simple kinetic model of matter, describe the structure of a solid.

Answer 24

Regularly shaped molecules very close together which vibrate about a fixed position.

Question 25

Describe how the Brownian motion provides evidence for the nature of the movement of gas molecules.

Answer 25

The random rapid motion of gas molecules causes them to collide with one another thus causes the smoke particles to change direction.