Thermal Physics

Question 1

How do you work out the internal energy of a body?

Answer 1

Find the sum of the kinetic energies and potential energies of all its particles

Question 2

How are the kinetic energies and potential energies distributed in a body?

Answer 2

Randomly

Question 3

How can you increase the internal energy of a body

Answer 3

1. Have work done to it to transfer energy to the system
2. Increase the temperature of the system

Question 4

What happens to the internal energy of a substance when it changes states

Answer 4

The internal energy changes:
Only the potential energy changes whilst the kinetic energy remains the same

Question 5

Why does only the potential energy changes when a substance is changing state

Answer 5

This is because energy inputted is used to break or make bonds between molecules rather than increase the temperature of a substance (from increasing kinetic energy)

Question 6

Definition of SHC and LH

Answer 6

SHC - energy required to increase the temperature of 1kg of a substance by 1 degree without changing the state of matter

LH - energy required to change the state of matter of 1kg of a substance without increasing the temperature

Question 7

What are the 3 gas laws

Answer 7

Boyles law = pV = k (when temperature is constant)
Charles law = V/T = k (when pressure is constant)
Pressure law = P/T = k (when volume is constant)

Question 8

How do you calculate Kelvin

Answer 8

K = C + 273

Question 9

What is absolute zero?

Answer 9

At 0 Kelvin, it is the temperature that particles have zero kinetic energy and the volume and pressure of a gas are zero

Question 10

State the ideal gas equation

Answer 10

pV = nRT

n = number of moles
R = molar gas constant

Question 11

What is 1 mole of substance equal to

Answer 11

1 mole of substance = 6.02*10^23 molecules/atoms

n = N/Na
N = number of molecules
Na = Avogadros constant
n = number of moles

Question 12

What is Molar mass?

Answer 12

It is the mass of one mole of a substance and can be found by finding the relative molecular mass

Question 13

What does the area in a pressure-volume graph indicate

Answer 13

Work done

Question 14

What causes a higher frequency of collisions in a system

Answer 14

• increased temperatures
• increased pressured
• decrease in volume

Question 15

What are the assumptions of the kinetic theory model?

Answer 15

• No intermolecular force
• Negligible Volume
• Duration of collisions is negligible
• Motion of particles is random
• Perfectly elastic collisions
• Motion of particles follows Newtons law
  -Particles move in a straight line

Question 16

What is an ideal gas

Answer 16

A gas that follows the gas laws perfectly, ideal gas has no potential energy so all of its internal energy is equal to the sum of its kinetic energies

Question 17

Explain why molecules of a gas exert a force on the walls of its container, refer to newtons laws of motion

Answer 17

There is a change in momentum on molecules because the direction has changed (F = ma)

Newton’s third law, when particle hits the wall it changes direction continue to extent force on the wall.

Question 18

Explain in terms of the kinetic theory model why pressure drops as volume increase

Answer 18

As volume increases
time between collision increases
speed remain constant due to temperature
- rate of change of momentum decreases