thermal physics

define internal energy

• sum of the randomly distributed kinetic energies and potential energies of the particles in a body

internal energy of a system is increased when

• energy is transferred to it

• by heating or when work is done on it

during a state change

• potential energies of particles changing

• kinetic energies do not change

specific heat capacity

• Q = mc delta theta

• the energy required to raise the temperature 1kg of a substance by 1K

specific latent heat

• Q = ml

when temperatures is changing

• kinetic energy is changing

• potential energy is constant

how atoms change their arrangement during melting or boiling

• energy transferred into system reduces the number of nearest atomic partners / atoms move their centre of vibration

how motion of the atoms changes during temperature rise

• mean kinetic energy of the atoms increases so their mean speed increases

specific latent heat of fusion

• energy required to change a unit mass of a substance from the solid state to the liquid state or vice versa

• without temperature change

temperature increase of air when speed of pump is higher

• greater work done on air molecules

• increases mean speed of articles and mean square speed

• therefore increases kinetic energy and temperature by 1st law of thermodynamics

pressure

• force per unit area that it exerts normally to the surfaces of a container

ideal gases

• potential energies between particles assumed to be 0

boyle’s law

• pressure is inversely proportional to the volume at a constant temperature for a fixed mass of gas

• $$P1V1=P2V2$$

• isothermal - any change at a constant temperature

charles’s law

• volume is proportional to its temperature at a constant pressure for a fixed mass of gas

• $$\frac{V1}{T1}=\frac{V2}{T2}$$

• isobaric - any change at a constant pressure

pressure law

• the pressure is directly proportional to its temperature at a constant volume for a fixed mass of gas

• $$\frac{P1}{T1}=\frac{P2}{T2}$$

• isochoric - any change at a constant volume

absolute 0

• temperature at which kinetic energy of the particles is 0

• 0k which is -273.15 celsius

• a state of minimum internal energy

degrees to kelvin

• +273

thermal equilibrium

• no overall heat transfer occurs between two objects at the same temperature

work done on a gas at a constant pressure

$$W=P\Delta V$$

number of moles, n in a mass

n = mass / molar mass

(molar mass is the mass of. mole)

number of molecules N

N = n x avogadro constant

ideal gas equation for number of moles

PV = nRT

• R is gas constant 8.31 Jmol^-1K^-1

• T is temperature in kelvin

• n is number of moles

ideal gas equation of number of molecules

PV = NkT

• k is boltzmann constant

• T is temperature in kelvin

• N is number of molecules

brownian motion

• smoke particles moving in random motion

• movement of smoke particles caused by collisions with randomly moving air molecules

• smoke particles are visible but air particles are not hence air molecules must be very small

• smoke particles are continuously moving because the air molecules are continuously moving