Thermal Physics Flashcards
What is the internal energy equal to
The sum of all the kinetic energies and potential energies of all its particles
How are all the kinetic energies and potential energies distributed in a body
Randomly distributed
What are the two ways you can increase the internal energy of a system
- do work on the system to transfer energy to it (e.g moving its particles/changing its shape)
- increase the temperature of the system
What happens to the internal energy as the state of the substance changes
The internal energy also changes
Why does the internal energy change when when the substance exchanges state
The potential energy of the system changes while the kinetic energy of the system is kept constant
How can we demonstrate that if a substance changes state the internal energy also changes
By measuring the temperature id water as it boils
- the temperature increases up until 100 degrees Celsius after which the energy gained through heating the water is no longer used to increase the temperature ( and therefore the kinetic energy) but instead is used to break bonds between water molecules so it can change state to water vapour and so the potential energy is increased
What equation can you use to measure the amount of energy required to change the temperature of a substance
Q = m x c x change in temp Q=energy required m=mass c=specific heat capacity
What is the definition of specific heat capacity
Is the amount of energy required to increase the temperature of 1kg of a substance by 1 degree Celsius/1k without changing state
What equation can be used to measure the amount of energy required to change the state of a substance
Q = m x l Q=energy required m=mass l=specific latent heat
What is the definition of specific latent heat
The amount if energy required to change the state of 1kg of material, without changing its temperature
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 do the gas laws describe
The experimental relationship between pressure volume and temperature for a fixed mass of gas
Are the laws based on a theory or from observation and experimental evidence
From observation and experimental evidence which means they are empirical in nature
What are the three laws
1 - Boyle’s law
2 - Charles’ law
3 - The pressure Law
What is Boyle’s and it’s equation
When temperature is a constant and pressure and volume are inversely proportional
PV = K
What is Charles’ law and its equation
When pressure is a constant, volume is directly proportional to absolute temperature
V/T = K
What is the pressure law and its equation
When volume is constant, pressure is directly proportional to absolute temperature
P/T = K
What temperature measured in when using the gas laws
Kelvin
What is the value of absolute zero
0K = -273°C
What happens to particles when they reach absolute zero and what happens to a gas
They have no kinetic energy and the volume and pressure of a gas are zero
What equation do you get when you combine all the laws of gas
PV/T = K
What dies K equal to in the equation PV/T = K and what is the rearranged equation
K = nR where n is the number of moles and R is the molar gas constant and the new equation is PV = nRT
What is the value of the molar gas constant
8.31
What is the value of 1 mole of a substance
6.02 x 10^23 atoms/molecules
What is the equation to covert between the number of moles and the number of molecules
N = n x Na N=the number of molecules n = the number of moles Na= the Avogadros constant
What are the two ideal gas equations
PV= nRT and PV= NkT
N is the number of molecules
K is the Boltzmann constant
What is the molar mass and how can it be found
Is the mass ( in grams ) of one mole of a substance and can be found by finding the relative molecular mass which is approx equal to the sum of all the nucleons in a molecule of the substance
What is the equation used to calculate work done on a gas to change its volume when it’s at constant pressure ( this is usually done through the transfer of thermal energy)
Work done = p x change in V
P = pressure
V = volume
How do you find the work done on a pressure volume graph
The area under the graph
what is Brownian motion
is the random motion of larger particles in a fluid caused by collisions with surrounding particles
how can Brownian motion be observed
looking through at smoke particles under a microscope
what did Brownian motion contribute evidence to
the existence of atoms and molecules
how can you use the simple molecular model to explain Boyle’s law
if you increase the volume of a fixed mass of gas, its molecules will move further apart so collisions will be less frequent therefore pressure decreases
how can you use the simple molecular model to explain Charles’ law
when the temp of a gas is increased, its molecules gain kinetic energy meaning they will move more quickly and because pressure is kept constant the molecules move further apart and volume is increased
how can you use the simple molecular model to explain pressure law
when the temp of a gas is increased, its molecules gain kinetic energy meaning they will move more quickly, as a volume is constant the frequency of collisions between molecules and their container increases and they collide at higher speeds therefore pressure is increased
what does empirical in nature mean
they are not based on a theory but arose from observation and experimental evidence
what are the 5 assumptions made in the molecular kinetic theory
- no 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 follow newtons laws
- the molecules move in straight lines between collisions
