thermal physics Flashcards
describe the structure of a solid
particles are fixed in a uniform lattice, where particles vibrate around their fixed positions
they are held in position by strong forces of electrostatic attraction
describe the structure of a liquid
particles are not fixed in position: they are constantly moving around but there are still some forces of attraction
describe the structure of a gas
particles are free to move around with constant random motion. there are no forces of attraction between particles in an ideal gas
define thermal equilibrium
no net transfer of energy; two bodies in thermal equilibrium have the same temperature
what is the celsius scale?
uses the freezing + boiling points of water to make a temperature scale
what is the kelvin scale?
also the thermodynamic scale does not depend on the properties of the substance
what value is absolute zero in degrees?
-273 degrees
convert degrees to kelvin
+273
what occurs when you heat a solid?
particles gain kinetic energy and vibrate more vigorously
eventually they may break away from the structure + become free to move around
when this happens, the solid has melted into a liquid
what occurs when you heat a liquid?
some of the particles gain enough energy to break away from other particles
particles that escape from the body of the liquid become a gas
what occurs when you heat a gas?
molecules collide with the container- these collisions are responsible for pressure which a gas exerts on the container
what is brownian motion?
particles move with random, zig zag motion
how could we observe Brownian motion?
put smoke in a brightly illuminated glass jar and observe particles using a microscope
smoke particles appear as bright specs moving haphazardly from side to side
how did Einstein prove the existence of atoms and molecules in the air?
randomly moving particles were hitting the smoke particles unevenly, causing this motion
define internal energy
the sum of the kinetic and potential energy of particles within a system
what is the relationship between kinetic energy and temperature?
directly proportional
what is potential energy caused by?
interactions between particles and is based on positions relative to each other
what happens to a substance when it’s heated?
temperature increases so kinetic energy increases and the internal energy increases
what happens when a substance changes phase?
the energy from the heat is used to alter and break the bonds within the substance but not to raise the temperature. as a result, the kinetic energy of the substance remains the same but the internal energy changes in order for it to change phase
define specific heat capacity
the amount of energy needed to raise the temperature of 1kg of a substance by 1 degree or 1 kelvin
give the equation for specific heat capacity
E= mcT
how could you measure the specific heat capacity of a solid or a liquid?
heat substance with a heater until there is a temperature change of 10K, recording the time taken to do this
attach an ammeter and voltmeter to heater to work out energy supplied using E=VIt
rearrange specific heat capacity equation to calculate c
define the specific latent heat of fusion
the amount of energy needed to melt or freeze 1kg of a substance
define the specific latent heat of vaporisation
the amount of energy needed to boil or condense 1kg of a substance
what is the equation for specific latent heat?
E=mL
how could you measure the specific latent heat of a solid or liquid?
place a heating coil and equal masses of ice in 2 funnels above the beakers
turn on one heating coil for 3 mins- record energy transferred
after 3 mins, measure the mass of water collected in beakers. subtract one from the other to get the mass of ice that melted solely due to presence of heater
use L= E/m to find slh
what 3 laws does an ideal gas obey?
Boyle’s law
Charles’ law
pressure law
what is Boyle’s law? give any supporting equations
at a CONSTANT TEMPERATURE, the pressure and volume of a gas are inversely proportional
higher temp= further curve from the origin
pV=constant
what is the pressure law? give any supporting equations
at a CONSTANT VOLUME, the pressure of a gas is directly proportional to temperature. P/T= constant
what is Charles’ law?
at a CONSTANT PRESSURE, the volume of a gas is directly proportional to its absolute temperature
what equation is given when you combine all 3 gas laws?
PV/T= constant
what is the gas constant?
8.31 J/mol/K
what is the ideal gas equation?
pV=nRT
what is Avogadro’s constant?
6.02x10^23
what equation can be used to find the number of particles?
N = n x Na
what equation can be used to find the Boltzmann constant?
k= R/Na
how can you get the equation pV=nKT
combine N = n Na and K = R/Na
Nk=nR
substitute into pV=nRT
to get pV=nKT
what is the Boltzmann constant?
1.38x10^-23 J/K
describe the motion of a gas in a container
- particles of the gas are free to move around with constant random motion
- there are no forces of attraction according to Newton’s 1st law
- they continue to move with constant velocity until they collide with another particle
what happens when a particle collides with a wall of a container?
a force is exerted on the box
the box exerts an equal and opposite force
Newton’s 3rd law
how can you calculate the force exerted by a particle on the wall of a container?
-using Newton's second law F= rate of change in momentum p=mu rebound = -mu so change in momentum=2mu forces by one particle = mass x velocity
describe how pressure arises from gases in a container
- the combined force from many particles is much larger, so lots of particles will be colliding with each wall at any given moment
- motion is random, collisions will be spread all over the surface of each wall
- result is a steady, even force on all walls of the box= pressure
give an equation found when combining kinetic energy and the ideal gas equation
pV=1/3Nmc^2
describe the effect of increasing volume
frequency of collision decreases as particles have further to travel between collisions
this decreases pressure
describe the effect of increasing the number of particles
increases the frequency of collisions between particles and container
this increases the pressure
describe the effect of increasing mass
greater force is exerted on the walls of the container (F=ma)
greater pressure
describe the effect of increasing speed
greater change in momentum as p=mv
this means a greater force is exerted
F= change in momentum over time
give the assumptions of the kinetic theory
- gas contains a large number of particles
- particles move rapidly + randomly
- collisions are perfectly elastic
- volume of particles in negligible when compared to the volume of the gas
- no forces between particles except in a collision
- length of time involved in a collision is negligible compared to time between collision
what name is given to a gas that obeys all assumptions of the kinetic theory?
an ideal gas
what does the Maxwell-Boltzmann distribution show?
it shows how the speeds of molecules are distributed in an ideal gas
as the temperature of a gas increases, what effect does it have on an ideal gas?
the average particle speed increases
the maximum particle speed increases
the distribution curve is more spread out
as a result of collisions, energy will be transferred between particles
some particles will gain speed in a collision whereas others will slow down
between collisions, how would you describe the speed of the particles?
they travel at constant speed
what equation is created when equating 1/3Nmc^2=NkT?
E=3/2kT
what is the relationship between average kinetic energy and internal energy to the absolute temperature?
directly proportional
a rise in absolute temperature will cause an increase in the kinetic energy of the particles, meaning a rise in internal energy
