3.6.2.1 - thermal energy transfer

what is heating?

energy transfer due to a temperature difference

what is thermal equilibrium?

no temperature difference between objects so heating does not occur.

objects are at same temp. no energy transfer.

what is heating ‘by particles’?

when energy is transferred by objects whose particles are moving at higher average speed to objects w/ lower avg speeds - due to the particles randomly colliding.

average speed of particles in an object depends on..

.. its temperature.

what is heating ‘by radiation’?

when energy is transferred via EM radiation by an object at higher temp to an object at lower temp.

when a hot block is placed on top of a cold block, describe and explain what happens

hot block - higher avg KE - vibrates faster

cold block - lower avg KE - vibrates slower

particles in hot block and cold block collide. KE from hot block transferred to cold block particles, making them have a higher avg KE

this occurs until both blocks have same avg KE.

when you heat an object, the average KE of particles…

…increases. particles vibrate faster. temperature increases

what is temperature?

a measure of the average KE of the particles that make up a solid, liquid or gas.

if the particles in an object has no kinetic energy, what is the motion of the particles like?

not moving at all. 0K.

what does the kelvin scale measure?

avg KE of particles

how to convert from degrees celsius to kelvin

kelvin = degrees celsius + 273.15

REMEMBER a change in degree celsius is the same in kelvin! e.g. temp difference of 47 to 56 degrees celsius is 9 degrees celsius but ALSO 9 kelvin

what two energies do particles have?

KE and potential energy

when a system changes from solid to liquid to gas, what happens to their KE energy and potential energy?

average KE increases (particles move faster), and average potential energy increases (particles further apart, less attractive force)

what are intermolecular forces? how are they affected during state change?

forces between molecules. During state change, SOME bonds are overcome (become weaker and weaker) , allowing the particles to be further apart

why are some intermolecular forces overcome during state change?

average potential energy increases: average distance between particles increases

define internal energy

the sum of the randomly distributed kinetic and potential energies of a system’s particles

define thermal energy

the sun of the randomly distributed kinetic energies of a system’s particle

State what happens to a system’s internal energy during heating and cooling.

During heating, energy is transferred to the system and its internal energy increases. (KE and PE increases)

During cooling, energy is transferred from the system and its internal energy decreases.

what happens to the average KE during a STATE-CHANGE

stays the same, as heat is being used to increase potential energy - weaken intermolecular bonds

explain how work done affects internal energy

when work is done ON a system, its int energy can increase

when word done BY a system its int energy can decrease

when energy is transferred by work can cause a change in thermal energy (kinetic energy of the particles within the system) and so can change internal energy of system