Thermal Physics Flashcards
absolute zero
The lowest possible temperature that any object can theoretically
around -273(.15)
Given the value of 0 kelvins
How to calculate kelvin
K = C + 273
Internal energy
The internal energy of a body is the sum of the randomly distributed kinetic and potential energies of all its particles
As the temperature of the gas increases
-the average particles speed increases
- The average kinetic energy of the particles increases
- the distribution curve becomes more spread out
Specific heat capacity
The amount of energy needed to raise the temperature of 1kg of the substance by 1K (or 1 degree)
Specific heat capacity
The amount of energy needed to raise the temperature of 1kg of the substance by 1K (or 1 degree)
Specific heat capacity equation
Energy change = mass x specific heat capacity x change in temperature
Q = mc x (change in temp)
Specific latent heat
SLH of fusion or vaporisation is the quantity of thermal energy needed to be gained or lost to change the state of 1kg of a substance
Specific latent heat equation
Energy change = specific latent heat x mass of substance changed
Q = ml
Boyles law
At a constant temperature and the pressure and the volume of a gas are inversely proportional
For example, if you reduce the volume of a gas its parcel will often be closer together and collide of each other and the container more often so the pressure increases
Ideal gas
An ideal gas is a theoretical gas that obeys Boyles law at all temperatures
Boyles law means that at any given temperature the product of p and V will always be the same
pV = constant
Pressure and volume graph
The higher the temperature of the gas the further the curve is from the origin
Charles law
At a constant temperature and the volume V of a gas is directly proportional to its absolute temperature T
And ideal gas also obeys Charles law
V and T are directly proportional to
At the lowest theoretically possible temperature, the volume is zero
If Charles law is a bid the volume divided by the temperature is constant
V/T = constant
When you heat gas, the particles gain kinetic energy and move more quickly
At a constant pressure this means they move further apart and so the volume of the gas increases
The pressure law
At constant volume the pressure of an ideal gas is directly proportional to its absolute temperature
For example, if you heat a gas the particles gain kinetic energy this means they move faster
If the volume doesn’t change, the particles will collide with each other and their container more often and at high speeds, increasing the pressure inside the container
At absolute zero the pressure is also also zero
If the pressure law is a base the pressure divided by the temperature is constant
P/T = Constant
Relative molecular mass
The sum of the relative atomic masses of all the atoms making up a molecule
Mole
An amount of substance containing Na particles all of which are identical
Na is avogadro constant
Avogadro constant value
6.02 x 10^23 mol^-1
Avogadro constant
The number of particles in a mole
Defined as a number of atoms in exactly 12 g of carbon isotope
Molar mass
The molar mass of a substance is the mass that one mole of the substance would have,(usually in grams) and is equal to its relative atomic or relative molecular mass
For example, the molar mass of helium (RAM = 4) is 4 g
molar gas constant, R
pV/T
putting in the values for 1 mole of an ideal gas at room temperature and atmospheric pressure gives the value
8.31JK-1
gas constant for one mole of gas
ideal gas equation
pV/T = nR
R = molar gas constant
n = number of moles of gas
boltzmann constant, k
k = R/Na
R = molar gas constant, 8.31
Na = avagadros constant
k = 1.38x10-23JK-1
gas constant for one mole of gas
N
N = n x Na
Nk = nR
ideal gas equation for N molecules
pV =NkT
work done equation
p x change in V
work done
for a gas to expand or contract pressure, work must be done (i.e energy transfer, normallu heat transfer)
e.g. heat a gas filled ballon = expand, remove heat = contract back to original size as heat is transferred back to surroundings
area under graph = energy transferred
change in momentum equation
mu-(-mu) = 2mu
time between collision of object equation
2l/u
number of coolisions per second equation
u/2l
rate of change of momentum equation
2mu x u/2l = muu/l
total force of all molecules on wall equation
F = m( u21 + u22 + etc.)/l
mean u squared
u21 + u22 + etc. / N
Total force with mean of u
F = Nm-u2 / l
derive pressure with force equation
pressure = force / area
p = Nm-n2 / lll == /v
same equation but intergrate c
if you treat all N molecules the same way, gives a mean square speed of -c2
-c2 = -v2 + -w2 + -u2
since molecules move randomly…
-v2 = -w2 = -u2
therefore -c2 = 3-u2
pV using 3-u2
pV = 1/3 X Nm-c2
-c2 mwaning
mean square speed of gas molecules in m2 s-2
root mean square speed
if -c2 is the average of the sqaures of speed of molecules, the sqaure rooy would be the typical speed
r.m.s speed = root mean sqaure speed ( root -c2 == Crms
Crms in pV equation
pV = 1/3 x Nm(Crms)^2
expalining charles law and pressure law
temperature is related to Ke of the molecules, as temperature increases, average speed of molecules increases, means rate of change of momentum of molecules colliding with walls of container increases so force on container increases
if volume is fixed, pressure change because
- more collisions between molecules and against wall in a given amount of time
- an average collision will result in larger change in momentum and exert a larger force on the wall
if pressure is fixed, volume will change because…
- if volume is larger, there will be longer time between collisions, so rate of change of momentum and force on wall will reduce
- as volume increases, SA of walls increases, pressure = force per unit area so increase in area stops incraese in pressure
Assumptions in kinetic theory
- all molecules of gas are identical
-gas contains large number of molecules
-molecules have negligable volume com pared with volume of container, acts as point masses
-molecules continually move randomly
-newtonian mechanics apply - collisions are elastic (Ke conserved)
-molecules m ove in straight lines after collisions
-forces that act during collision for less time than between collisions
A gas obeying these assumptions = ideal gas
assumption of internal energy for an ideal gas
For an ideal gas you assume all internal energy is in the form of Ke
means you can use the product of pV to find average and total Ke
combing equations
1/3 Nm (Crms)^2 = nRT
3/2 X 1/3 Nm(Crms)^2 = 3/2 x nRT
1/2 m(Crms)^2 = 3/2 nRT / N
sub Nk for nR
3/2 X NkT / N
1/2 m(Crms)^2 = 3/2 x kT
K = R/Na
1/2 m(Crms)^2 = 3/2 x RT / Na
emprical laws
laws based on observations and evidence
they can predict what will happen but cant explain why
kinetic theory
based on a theory
means its based on assumptions and derivations from knowledge and theories we already had and will both predict and explain why a change occurs
develpment of gas laws
Ancient Greek and Roman philosiphers had ideas about gas 2000 years ago
Robert Boyle discovered the relationship between pressure and volume at a constant temoeratire in 1662
Jacques Charles discovered volume is proportional to temperature at a constant pressure in 1787
Guillaume Atomons in 1699 noticed at a constant volume, pressure is proportional to temperature
in 1827 robert brown discovered brownian motion
Brownian motion
Rober brown noticed pollen grains moved in water in a zig zag
this type of movemnt of any particles suspended in a fluid is known as brownian motion
brwnian motion einstein
Einstein shown brownian motion supported kinetic theory model of different states of matter and that the random motion is due to the collisions with fast, randomly moving particles in a fluid
brownian motion smoke example
can see brownian motion when large heavy particles like smoke move with brownian motion by smaller lighter particles like air travelling at high speeds
this is evidence that air is made up of tiny atoms moving really quickly
