Thermal properties of matter

Question 1

Define internal energy

Answer 1

Internal energy of a substance is the sum of kinetic energy due to random motion of particles and potential energy due to forces of attraction between particles

Question 2

Define heat capacity

Answer 2

Heat capacity, C, is the amount of heat required to raise the temperature of a substance by 1K

Question 2

Define specific heat capacity

Answer 2

Specific heat capacity, c, is the amount of heat required to raise the temperature of a unit mass of a substance by 1K

Question 3

What are the 2 types of latent heat

Answer 3

• Latent heat of fusion
• Latent heat of vaporisation

Question 3

Define latent heat

Answer 3

Latent heat is the energy released or absorbed to change the state of a substance at constant temperature

Question 4

Describe melting in terms of particles

Answer 4

• Energy supplied to do work against forces of attraction between particles
• Particles have wider range of movement and average distance between particles increases
• Internal energy of substance increases
• Kinetic energy of substance remains the same, so temperature remains constant

Question 5

Describe freezing in terms of particles

Answer 5

• Energy released to surroundings causes forces of attraction to reform around particles
• Average distance between particles decreases
• Internal energy of substance decreases
• Kinetic energy of substance remains the same, so temperature remains constant

Question 6

Define specific latent heat of fusion

Answer 6

Specific latent heat of fusion is the amount of heat required/released to change a unit mass of a substance between solid and liquid states at constant temperature

Question 7

Define specific latent heat of vaporisation

Answer 7

Specific latent heat of vaporisation is the amount of heat required/released to change a unit mass of a substance between solid and liquid states at constant temperature

Question 7

Define evaporation

Answer 7

Evaporation is the process where a liquid changes to a gas without boiling

Question 8

What are some differences between evaporation and boiling

Answer 8

• Boiling occurs at fixed temperature
• Boiling occurs throughout the liquid
• Bubbles formed during boiling
• Temperature remains constant during boiling

Question 8

Describe how evaporation occurs

Answer 8

• Particles in liquid are always moving randomly at different speeds
• Particles at liquid surface can escape to atmosphere as long as they have sufficient kinetic energy to overcome attractive forces of other liquid particles and do work against atmospheric pressure
• Less energetic particles are left behind
• Average kinetic energy of liquid particles decreases
• Average liquid temperature decreases