Heat and Temperature

Temperature

a measure of the average kinetic energy of each particle in a substance

Heat

The Kinetic energy transferred from one to another due to a temperature difference

What can be used to measure heat?

calorimeter

Factors affecting heat

number of particles in substance

The energy of the particlesoparticles o

conduction

energy transfer between particles in contact

convection

the circulation of fluids as warm fluids rise due to a density decrease

radiation

electromagnetic waves emitted due to an objects temperature

Specific heat capacity

the amount of energy required to change the temperature of 1kg of a substance by 1K

Specific latent heat

the amount of energy required to change the state of 1 kg of a substance

Internal energy (U)

The total potential and kinetic energy of all the particles in a substance combined

Potential energy

The energy in the chemical bonds and atoms themselves

Specific latent heat of vaporisation

the energy needed to push liquid particles further apart , changing the substance into a gas

Specific latent heat of fusion

The energy needed to break bonds in a substance to change it from solid to liquid

Why are values for L_{vapourisation} typically higher than values for L_fusion?

Gas molecules have larger intermolecular space, and the force of attraction between the particles is almost negligible, so more energy is needed to push the particles apart.

Black body radiation

A body that completely absorbs all the radiation incident upon it and emits all of the radiation in a particular distribution of wavelengths

Luminosity

The total amount of radiation a black body emits per second (measured in watts)

Colour of 3000K star

red

Colour of 3000K star

red

How does increase in temperature affect Boltzmann distribution?

peak is lower and shifts to right

Assumptions for particles in Boltzmann distribution

no molecules with 0 energy

Only a few molecules have a very high energy

There is no maximum energy a molecule can have

Each curve is for one specific temperature

Gay-Lussac’s law

for a constant mass of gas at constant volume, the pressure exerted by a gas is proportional to its temperature

Absolute 0

the lowest theoretical temperature possible where entropy reaches its minimum, and molecules have the lowest possible internal energy

Why can’t absolute 0 be reached in practice?

surroundings of the matter must also be at absolute 0 to prevent heat transfer, and all matter have 0 point energy (a minimum energy that cannot be lost)

Why does pressure increase with temperature?

Higher T → Higher E_k → higher v

So particles collide more often with a higher rate of change of momentum

Why does pressure increase when volume decreases?

less time between collisions, more particles per m³, so higher rate of collisions with more force (higher rate of change of momentum)

Boyles law

For a fixed mass of gas at a constant temperature, The product of pressure and volume is constant

Graph of V on x axis, p of y axis

curve with negative gradient

How does increasing temperature affect a graph of 1/V against p?

gradient of straight line increases

Components of refrigeration in order

Expansion valve

Internal coil

Compressor

External coil

What does the expansion valve do?

Expands refrigerant

Increased V, so gas particles bounce off with lower v

So T of refrigerant decreases

What does the internal coil do?

low v gas particles bounce off vigorously vibrating particles of coil

Gas particles bounce off with higher v, amplitude of vibrating solid particles decrease

T of coil and surroundings decreases

What does the compressor do?

Compresses refrigerant

Decreases V, so gas particles bounce off with higher v

So T of refrigerant increases

What does the external coil do?

High v gas particles bounce off slow vibrating particles of coil

Gas particles bounce off with lower v, amplitude of vibrating solid particles increase

T of coil and surroundings increases

Charles’ Law

for a constant mass of gas at fixed pressure, the volume occupied by the gas is proportional to its absolute T

Uncertainty principle

you can’t know both the exact position of a particle AND its momentum unless it is at absolute 0 (when the zero-point energy has been reached)

Ideal gas assumptions

molecules are identical and in constant random motion

Newtons laws of motion are applicable to molecules

Volume of individual molecules are negligible

No forces act on the molecule except for when they collide

Large number of molecules

Collisions have negligible duration and are elastic