b1 | thermal energy transfers

the kinetic theory of matter is a model that…

attempts to explain the properties of the three states of matter

in the kinetic theory of matter, particles are assumed to be…

small spheres

the difference between solid ice, liquid water and gaseous steam is…

the arrangement of the particles

particles in a solid are … packed

closely

particles in a solid are arranged in a fixed … structure

lattice pattern

particles in a solid can only … about their fixed positions

vibrate

particles in a solid have … energies compared to particles in liquids and gases

low

particles in a solid do/do not have enough energy to overcome the intermolecular forces of attraction holding them together because of …

do not | low energies compared to liquids and gases

solids have a fixed … and …

shape | volume

solids are very … to compress

difficult

solids have lower/higher densities that liquids and gases

higher

particles in a liquid are … packed

closely

particles in a liquid are … arranged

randomly

particles in a liquid can/cannot flow past each other

can

liquids have higher energy than … but less than …

particles in solids | gas particles

liquids have enough energy to …. overcome the intermolecular forces of attraction

partially

liquids do/do not have a fixed shape

do not

liquids have a … volume

fixed

liquids are easy/difficult to compress

difficult

particles in a gas are close to each other/far apart

far apart

particles in a gas are … arranged

randomly

gases move around …. at a … of speeds

in all directions | variety

gases occasionally collide with …. and ….

each other | walls of the container

gases have high/low density

low

gases have higher energies than …

solids and liquids

gases can/cannot overcome the intermolecular forces

can

density is the …. of an object

mass per unit volume

if two objects occupy the same volume the object with a lower density will have a …

lower mass

formula for density?

density = mass/volume of container

absolute zero refers to…

the lowest possible temperature, at which the molecules ina substance have zero kinetic energy

absolute zero is equal to …K or …C

0 | -273

it is not possible to … from a system at 0K

remove any more energy

the melting point of ice is …K and …C

273 | 0

because particle in gases usually have a range of speeds, the average kinetic enegry can be calculated using…

E k = 3/ 2 k _B T

explain this formula: E k = 3/ 2 k _B T

3/2: comes from the number of translational degrees of freedom for a particle in three-dimensional space (x, y, z). Per degree, the energy contribution is 1/2k_BT.

K_B: converts between temp(K) and energy(joules).

K_B: 1.38 × 10^-23J/K

T: absolute temperature of the gas(K)

this graph shows that…

the absolute temperature of a body is directly proportional to the average kinetic energy of the molecules within the body

in the average kinetic energy of molecules E_K at the start of the formula can be equated with…

1/2mv²

when a substance gains or loses thermal energy what increases or decreases?

thermal energy

the internal energy of a substance is the sum of…

total kinetic energy and total intermolecular potential energy

an increase in potential energy occurs when..

particles move further away from each other, because work is being done to overcome the attractive forces

an increase in average kinetic enegry occurs when… OR/AND …

molecules vibrate | move at higher speeds

an increase in temperature is brought about by an increase which of the below?

average kinetic energy | potential energy

average kinetic energy

due to thermal expansion what increases with the temperature of a substance…

the potential energy of the molecules

does potential energy change cause temperature change?

nono extent

to what extent does temperature change occur with state change?

no extent

does a change in internal energy correspond with a change in temperature? why or why not?

no, because change in potential energy doesn’t change temperature

thermal energy is a fancy word for?

heat

thermal energy is transferred from … to …

hotter region | lower region ther

thermal energy transfer stops when…

both regions are the same temperature

thermal equillibirum is when…

two substances in contact with each other no longer exchange any heat energy and both reach an equal temperature

during a phase change what is transferred to or from the substance?

thermal energy

what doesn’t change during phase change?

temperature

the thermal energy provided or removed does not affect… but it does affect …

kinetic energy | potential energy(spacing between atoms)

condensation is …. and … thermal energy

gas to liquid | releasing

melting and boiling occurs when thermal energy is…

absorbed

melting and freezing happen only at…

the melting/freezing point

vaporisation and condensation happen only at…

the boiling point of a substance

every substance has a unique/the same boiling/freezing point?

unique

the amount of thermal energy to change the temp of an object depends on what three things?

the mass of the object

• the greater the mass the more energy is needed

the specific heat capacity

• the higher the more energy is needed

change in temperature wanted

• the larger the change the more energy required

thermal energy is the amount of energy required to…

cause a temperature change, depending on the substance's mass and specific heat capacity

the formula for thermal energy transferred is

Q = mc change in temp

the specific heat capacity is the energy required to change the temperature of …. of a substance by ….

1kg |1K or 1C

the higher the specific heat capacity…

the longer it takes for the substance to warm up or cool down

during a phase change, the temp of the substance changes/does not change

does not change

when temperature of a substance does not change thermal energy can be calculated by

how can thermal energy increase without a temperature change?

because during a state change the energy goes into changing the state of the substance not increasing kinetic energy

the energy used to overcome intermolecular forces is…

latent heat

what is latent heat stored as?

potential energy

even though thermal energy is added temp remains constant because

all the energy is used for phase transition

latent heat is defined as the amount of energy required to…

change the state of 1kg of a substance without changing the temperature

the higher the specific latent heat…

the greater the energy required to change its state

is the specific latent heat for melting and freezing the same?

no

specific latent heat of fusion is the energy released/absorbed when

1kg of solid/liquid freezes/melts to become solid/liquid at constant temp

fusion applies to…

melting

freezing

specific latent heat of vaporisation is the energy released/absorbed when..

1kg of gas/liquid condenses/evaporated to become liquid/gas at constant temp

vaporisation applies to…

evaporation

condensation

latent heat of vaporisation > specific latent heat of fusion because…

intermolecular forces must be completely overcome to transfer from liquid to gas but not for solid to liquid

• vaporisation = more energy

what can thermal energy be substituted for in equations?

P = E/t

E = Pt

explain this graph in terms of flat sections, non-flat section

state what type of curve it is

heating curve

explain this graph in terms of flat sections, non-flat section

state what type of curve it is

cooling curve

what are the three mechanisms of thermal energy transfer

radiation

convection

conduction

objects will always lose heat until…

they are at thermal equilibrium with their surroundings

conduction occurs when thermal energy is transferred between two objects…

in contact with one another

metals are the best thermal conductors because…

they have a high number of delocalised electrons

• faster rate of transfer of vibrations

liquids and gases are poor thermal conductors because…

the atoms are further apart

what two mechanisms can conduction occur through?

atomic vibrations

free electron collisions

explain the process of atomic vibrations and free electron collisions in conduction?

the hotter atoms vibrate more so when they collide with the cooler ones they transfer energy until thermal equilibrium is reached

what is a free electron?

an electron that is not bound within the atom and is free to move

thermal conductivity is the ability of a substance to…

transfer heat via conduction

good thermal conductors have what three things?

high values of thermal conductivity

fast rate of thermal energy transfer

large number of delocalised electrons

a temperature gradient is when…

in the presence of a temperature difference, thermal energy flows from the region of higher temp to the region of lower temp

the formula for the rate of heat transfer is

k = thermal conductivity of the material (W m K )

A = cross-sectional area (m )

ΔT = temperature difference (K or °C)

Δx = thickness of the material (m)

is the flow of thermal energy per second across a temperature gradient uniform or non-uniform?

uniform

convection occurs when a fluid…

is heated causing the movement of groups of atoms/molecules due to density variations

convection cannot occur in… because..

solids | particles cannot travel relative to one another

what happens when a fluid is heated from below, so in a convection current?

the increase in E_K causes the molecules to push each other apart so the fluid expands

as the hot fluid is less dense it rises

the cool fluid moves in to take its place

eventually the hot fluid cools, contracts and sinks back down

a perfect black body is an object that…

absorbs all of the radiation incident on it, and does not reflect or transmit any

a good absorber is also a…

good emitter

an object which completely absorbs all radiation will be black because…

the colour black is what is seen when all colours from the visible light spectrum are absorbed

black body radiation is…

the thermal radiation emitted by all bodies