thermal properties of matter

Question 1

define heat capacity

Answer 1

the amount of heat required to raise the temperature of the object by 1K or 1°C

Question 2

SI unit for heat capacity

Answer 2

J/K

Question 3

formula for heat capacity

Answer 3

C = Q (absorbed or released heat)/x (change in temp)

Question 4

define specific heat capacity

Answer 4

the amount of heat required to raise the temperature of 1kg of the object by 1K or 1°C

Question 5

SI unit for specific heat capacity

Answer 5

J kg-¹K-¹
OR
J (kg/K)

Question 6

formula for specific heat capacity

Answer 6

C = Q (absorbed or released heat)/ mass × x (change in temp)

Question 7

define internal energy

Answer 7

total amount of kinetic and potential energy the particles of an object possess

Question 8

explain kinetic energy

Answer 8

KE is due to the motion of particles and is directly related to temperature

Question 9

explain potential energy

Answer 9

PE is due to the stretching and compression of intermolecular bonds as the particles move.

PE is dependent on forces between particles and how far apart they are.

Question 10

define melting

Answer 10

melting is a process in which a substance changes in state from solid to liquid, without a change in temperature

Question 11

what is latent heat of fusion

Answer 11

the thermal energy absorbed during melting process/ the thermal energy released during solidification

Question 12

explain the energy transfer during melting

Answer 12

when ice begins to melt, thermal energy is absorbed to break the bonds between the particles of solid ice.
only the total internal potential energy increases, and kinetic energy of particles remains the same, thus temperature does not change during melting.

Question 13

define solidification

Answer 13

solidification is a process in which a substance changes its state from liquid to solid, without a change in temperature.

Question 14

explain the energy transfer during solidification

Answer 14

when liquid freezes, strong bonds are formed when particles move closer together.
only the total internal potential energy increases, and kinetic energy of particles remains the same, thus temperature does not change during melting.

Question 15

define boiling

Answer 15

boiling is the process in which a substance changes from the liquid state to the gaseous state, without a change in temperature

Question 16

explain boiling in terms of molecules

Answer 16

during boiling thermal energy is used to break the bonds between water molecules, and to provide energy for the molecules to push back on the surrounds to escape into the air.

Question 17

define condensation

Answer 17

condensation is the change of state from vapour to liquid, without a change in temperature

Question 18

explain condensation in terms of molecules

Answer 18

at the condensation point, the substance releases thermal energy as bonds are formed between the particles.

when steam condenses, it releases latent heat of vaporisation

Question 19

define latent heat of fusion/vaporisation

Answer 19

it is the amount of thermal energy required to change a substance from solid to a liquid / liquid to gaseous, without a change in temperature

Question 20

define specific latent heat of fusion

Answer 20

it is the amount of thermal energy required to change unit mass of the substance from solid to a liquid / liquid to gaseous, without a change in temperature

Question 21

formula for specific latent heat of fusion/vaporisation

Answer 21

lf / lv = Q (amt of heat) / m (mass)

Question 22

SI unit for specific latent heat of fusion/vapourisation

Answer 22

J/kg

Question 23

explain evaporation

Answer 23

evaporation occurs when a liquid changes in state to a gas, below its boiling point

• molecules are in continuous, random motion at different speeds
• more energetic molecules have the energy to overcome attractive forces due to other molecules and escape from the surface into the atmosphere
• less energetic molecules are left behind and the average KE of the molecules decrease, so the temperature decreases

Question 24

list factors that affect the rate of evaporation

Answer 24

temperature ↑↓
surface area
humidity ↑↓
boiling point of liquid
pressure
movement of air