thermal properties of matter

Question 1

kinetic energy

Answer 1

• motion of molecules, avg speed of molecules

- related to temp

Question 2

potential energy

Answer 2

• inter-molecular forces between the molecules

- avg distance between molecules, separation between molecules

Question 3

temperature is a measure of what

Answer 3

average kinetic energy of the molecules

Question 4

zeroth law of thermodynamics

Answer 4

two systems that are in thermal equilibrium with a third system are in thermal equilibrium with each other.

the temperature of a system determines whether the system is in thermal equilibrium with another system.

two systems are in thermal equilibrium if and only they have the same temp

Question 5

heat capacity (C)

Answer 5

heat capacity (C) of a substance is the amount of thermal energy required to raise the temperature of a substance by 1K

S.I. unit -> JK^-1

C = mc

C = Q/🔺teeter

Question 6

specific heat capacity (c)

Answer 6

amount of thermal energy required to change the temperature of 1kg of substance by 1K

S.I. unit -> JKg^-1K^-1

c = (1/m)(Q/🔺teeter)

Q = mc🔺teeter

Question 7

formula for energy

Answer 7

energy Q = P x t

P = power of appliance (in Watts W or J/s)

t = time

Q = total quantity of energy supplied

Question 8

melting (same for boiling, condensation , solidification)

Answer 8

melting is a process whereby there is a change of state from solid to liquid without a change in temperature

Question 9

latent heat of fusion (same as latent heat of vaporization)

Answer 9

thermal energy required to change the substance from solid state to liquid state or from liquid state to solid state w/o and change in temperature

S.I. unit J

Question 10

specific latent heat of fusion (same as specific latent heat of vaporization)

Answer 10

thermal energy required to change 1kg of substance from solid state to liquid state or liquid state to solid state w/o any change in temperature

S.I unit Jkg^-1

Question 11

evaporation

Answer 11

evaporation is a process whereby a substance changes its state from liquid to gas at any temperature

Question 12

process of evaporation

Answer 12

1. the molecules in the liquid are always moving randomly at different speeds or different kinetic energies
2. at the surface of the liquid, the fast moving liquid molecules, that have enough energy to overcome the downward attractive forces of other liquid molecules and overcome the atmospheric pressure, escape into the atmosphere or the space above the surface.
3. the less energetic molecules are left behind in the liquid. the average kinetic speed and kinetic energy of the molecules in the liquid decrease, lowering the temperature of the liquid

Question 13

ways to increase rate of evaporation

Answer 13

1. increase area of the liquid surface (exposed to surroundings)
2. increase temp of liquid (increase average kinetic energy of molecules)
3. increase movement of surrounding air above the liquid surface (to remove water water molecules that gather above the surface of the liquid before they have a chance to return to it)
4. reduce the air pressure above the liquid

Question 14

factors affecting boiling point

Answer 14

⬆️ pressure, ⬆️ boiling pt

⬇️ pressure, ⬇️ boiling pt

impurities ⬆️ boiling pt

Question 15

factors affecting freezing point

Answer 15

impurities ⬇️ freezing point

Question 16

people who use the steam machine must be careful not to injure themselves. explain why a jet of steam at boiling point is more dangerous Han the same mass of boiling water

Answer 16

a jet of steam has higher internal energy compared to the same mass of boiling water

when steam lands on the skin (compared to when boiling water lands on the skin), an additional amount of energy in the form of latent heat of vaporisation is also transferred onto the skin, causing more severe burn as latent heat of vaporisation is a large amount of energy

Question 17

when a cup of coffee is left on the table for some time, it cools down. explain, in molecular terms, how evaporation causes the coffee to cool down

Answer 17

when water evaporates, the molecules with higher than average kinetic energy escape from the liquid surface, leaving the molecules with lesser than average kinetic energy in the liquid.

hence the average kinetic energy of the molecules in the liquid decreases. therefore the temperature of the coffee decreases and the coffee cools down

Question 18

star and explain, if energy lost to the surroundings is taken into account how the value of specific heat capacity of liquid x calculated in (c)(iii) would be different

Answer 18

value larger

same amount of thermal energy supplied by the heater per unit time is now transferred to both the surroundings and to liquid x

more energy is required to raise the temp of liquid x and the time taken to heat up the liquid to the same temp would be longer

Question 19

explain, using the kinetic theory of matter, why the temp remained constant from the time 5min to 8min

Answer 19

cuz energy supplied does not increase the average kinetic energy of the molecules

thermal energy supplied and absorbed is used to overcome the intermolecular forces of attraction between the molecules of the liquid and separate them further apart

and to do work to expand against the atmospheric pressure

or to do work to overcome the forces exerted on the surface of the liquid by atmospheric pressure

Question 20

internal energy

Answer 20

sum of molecular kinetic energy and molecular potential energy in a body