9p2 Thermodynamics Flashcards
What is specific heat capacity and the equation to find it
The amount of energy required to increase the temperature of 1kg of a substance by 1oC/1K, without changing its state
Energy (J) = mass (kg) x specific heat capacity x temperature
What is specific latent heat and the equation to find it
It is the amount of energy required to change the state of 1kg of material without changing its temperature
Energy (J) = specific latent heat x mass (kg)
What are the two types of specific latent heat
Specific latent heat of fusion - when solid changes to liquid
Specific latent heat of vaporisation - when liquid changes to gas
What is internal energy
The internal energy of a body is equal to the sum of all the kinetic energies and potential energies of all its particles - the kinetic and potential energies are randomly distributed
What happens to the components of internal energy when the state of a substance changes
Potential energy of the system changes while the kinetic energy of the system is kept constant
What is absolute zero temperature
-273oC or 0K it is the lowest possible temperature at which the particles have no kinetic energy and the volume and pressure of the gas is zero
What is the Kelvin scale and how to convert to Celsius
It is the absolute scale of temperature
K = C + 273
How is the average kinetic energy and absolute temperature related
They are directly proportionate
Average molecule kinetic energy = 3/2kT
Where k is the Boltzmann constant and T is the temp in kelvin
What are the assumptions for the kinetic theory model
- the intermolecular forces act on the molecules
- the duration of collisions is negligible in comparison to time between collisions
- the motion of molecules is random and they experience perfectly elastic collisions
- the motion of the molecules follows newton’s laws
- the molecules move in straight lines between collisions
What is an ideal gas
In an ideal gas there is no other interaction other than perfectly elastic collisions between the gas molecules - therefore shows no intermolecular forces between molecules - so an ideal gas has no potential energy - so all its internal energy is the sum of the kinetic energies of all its particles
what is the equation associated with ideal gases
pV =NkT
p is pressure, V is volume, N is number of molecules and T is absolute temperature
What is a black body radiator
A perfect emitter and absorber of all possible wavelengths of radiation
What is stefans law
The power output (luminosity) of a black body radiator is directly proportionate to its surface area and absolute temperature
L = oAT^4
Where o is the Stefan constant 5.67x10^-8
What is wiens law
The peak wavelength of emitted radiation is inversely proportional to the absolute temperature of the object
Peak wavelength x T = constant = 2.898 x 10^-3 mK
Where mk is metres-Kelvin
What does Weins law show
As the temperature of the body increases, the peak wavelength decreases
How is the motion of gas molecules described?
Gas molecules move with Brownian motion, which is the random motion of molecules caused by collisions with larger particles.
How does a gas exert a force on its container?
The molecules collide with the walls of their container. Collisions cause a change in momentum, producing a force equal to the rate of change of momentum.
What does Boyle’s Law state?
When a gas is at a constant temperature, pressure and volume are inversely proportional to each other.
Explain Boyle’s Law.
When the volume of a gas increases, the space between molecules increases and the time between collisions is larger, causing the rate of collisions and the rate of change of momentum to decrease.
What does Charles’ Law state?
When a gas is at a constant pressure, the volume is directly proportional to the absolute temperature.
Explain Charles’ Law.
As temperature increases, the average kinetic energy of the molecules increases. Pressure is constant, so the volume increases to compensate for the faster speed of the molecules.
What does the Pressure Law state?
When a gas has a fixed volume, pressure is directly proportional to the absolute temperature.
Explain the Pressure Law.
As temperature increases, the average kinetic energy and speed of the molecules increase, leading to a larger rate of collisions and an increase in pressure.
What follows all the assumptions made in kinetic theory?
Ideal gases.
Combine the relationships between pressure, volume and temperature into a single expression, with a constant.
pV = constant.
How do you convert between the number of moles and number of molecules in a sample?
Multiply the number of moles by the Avogadro constant.
State the equation linking the pressure and volume of a gas to the speed of its molecules.
pV = ⅓ Nm⟨c²⟩.
What is the peak wavelength?
The peak wavelength is the wavelength at which the emitted radiation is most intense.
