Unit 3 Flashcards
What does Stefan-Boltzmann law show?
Stephen Boltzmann law shows the relationship between the temperature of a black body and the power emitted by the blackbodies surface area
What does the triple point of water mean
The unique temperature and pressure at which water can exist as liquid water, ice and water vapor
What’s is teh internal energy of a substance ?
The internal energy of a substance is a total of the potential energy and the random kinetic energy of all the particles in the substance
The sum of the total kinetic energy and the total intermolecular potential energy of the particles within the substance
What is NSE’s trading system called ?
NEAT : national exchange for automated trading
What is maximum brokerage prescribed by SEBI ?
2.5%
thermal interaction
When thermal energy is exchanged, the objects (or systems) involved are said to have a thermal interaction
heat
The thermal energy exchanged during a thermal interaction is referred to as heat
Temperature (3)
The temperature of an object is a macroscopic measure of the average kinetic energy of the particles (atoms or molecules) that make up the object
Absolute zero(2)
Absolute zero is a temperature of zero kelvin (0 K) and corresponds to the temperature at which the average kinetic energy of the molecules is at its minimum
Why does temperature of the substance no change during state change ? 2
- Since temperature is a measure of the average kinetic energy of the molecules, only an increase in the average kinetic energy of the molecules will result in an increase in temperature of the substance
- When only the potential energy of the molecules changes( i.e. the particles get further away from each other or move closer to each other ), the temperature of the substance does not change. This is the case for all state changes (e.g. melting, boiling)
a change in internal energy does not necessarily corresponds to a change in temperature. Explain (2)
As thermal energy is transferred to a substance, two things can happen:
An increase in the average kinetic energy of the molecules corresponds to a change in temperature
Or
A change in the average potential energy of the molecules does not affect temperature(change in state)
The amount of thermal energy needed to change the temperature of an object depends on: 3
The change in temperature required ΔT - i.e. the larger the change in temperature the more energy is needed
The mass of the object m
The specific heat capacity c of the given substance
specific heat capacity of a substance is defined as:
The amount of energy required to change the temperature of 1 kg of a substance by 1 K (or 1°C)
The specific latent heat of a substance is defined as:
The amount of energy required to change the state of 1 kg of a substance without changing its temperature
two types of specific heat:
Specific latent heat of fusion, Lf
Specific latent heat of vaporisation, Lv
Specific latent heat of fusion is defined as:
The energy released when 1 kg of liquid freezes to become solid at constant temperature
Specific latent heat of vaporisation is defined as:
The energy released when 1 kg of gas condenses to become liquid at constant temperature
The energy released when 1 kg of gas condenses to become liquid at constant temperature
Why is much more energy is needed to evaporate (or condense) a substance than it is needed to melt it (or solidify it) ?
In melting, the intermolecular bonds only need to be weakened to turn from a solid to a liquid
When evaporating, the intermolecular bonds need to be completely broken to turn from liquid to gas. This requires a lot more energy.
Is work done by or on teh gas ?
The volume decreases, therefore, work is done by the gas (work is also negative in thsi case’
The First Law of Thermodynamics
change in internal energy = heat added + work done on the system
Conservation of energy
Entropy 3 definitions
- the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work
- Measure of disorder in a system
- The entropy S of a given system is a measure of the number of possible arrangements of the particles and their energies
reversible process(macroscopic level)
A process where there is no overall change in entropy as the system and its surroundings are returned to their original states
Irreversible process(macroscopic level)
A process which results in an increase in entropy as the system and its surroundings cannot return to their original states
Why does the entropy of a real isolated system always increase ?
Processes in real isolated systems are almost always irreversible and consequently, the entropy of a real isolated system always increases
isolated system
A system in which neither matter nor energy can be transferred in or out
entropy of a system two formulas :
Macroscopic level : S = Q/T
Microscopic Level : S = k(B) In Ω
microstate
A microstate describes the number of states or possible arrangements of the particles in the system
Ω
Ω = the number of possible microstates of the system
What do microstates help do ?
microstates as a way of quantifying the certainty of information we have about the system
Eg! A solid has lower entropy than a gas because we can be more certain about the location of the atoms in the solid
Second Law of Thermodynamics
In every process, the total entropy of an isolated system always increases
Clausius form of the second law states:
Thermal energy cannot spontaneously transfer from a region of lower temperature to a region of higher temperature
Why is the word spontaneous improtant in the Clausius form of teh second law ?
The use of the word ‘spontaneously’ is the key here, as heat pumps are an example of a way that heat can be transferred from a colder region to a hotter one by doing work
the Kelvin form of the second law
When extracting energy from a heat reservoir, it is impossible to convert it all into work
The four main thermodynamic processes are
Isovolumetric
Isobaric
Isothermal
Adiabatic
An isobaric process is defined as:
A process in which no change in pressure occurs
An isovolumetric process is defined as:
A process where no change in volume occurs and the system does no work
adiabatic
A process where no heat is transferred into or out of the system
heat engine
A heat engine is a device that converts thermal energy into mechanical work
closed cycle
A closed cycle is one in which the system returns to its initial state
Carnot cycle
A thermodynamic system that runs at its greatest possible efficiency follows a cycle called the Carnot cycle
The total power P radiated by a perfect black body depends on two factors:
It’s absolute temperature
It’s surface area
Conduction
Which is the transfer of thermal energy via intramolecular collisions
Convection
Which is the transfer of thermal energy via bulk movement of a fluid due to a change of density
Radiation
Which is the transfer of thermal energy via electromagnetic waves (or words to that effect)
Wavelength, frequency and energy correlation
As wavelength decreases, frequency increases and energy increases
Wavelengths and temprature
Lower wavelength corresponds to higher temperatures
Wien’s law
λmax = b / T
where: λmax is the wavelength at peak radiation intensity in meters. b is Wien’s constant in meter-kelvin. T is the absolute temperature in kelvin.
0.0029
Emissivity
The power radiated by a surface divided by the power radiated from a black body of the same surface area and temperature
Perfect black body
An object that absorbs all of the radiation incident on it and does not reflect or transmit any radiation
Emissivity
The power radiated by a surface divided by the power radiated from a black body of the same surface area and temperature
