Thermodynamics (9) Flashcards
What is the definition of specific heat capacity?
The energy required to raise the temperature of one kilogram of a substance by one kelvin.
What three factors determine the increase in temperature of an object?
The amount of heat energy transferred, the mass of the object, and the specific heat capacity of the material.
What is the formula for calculating heat energy transfer?
ΔE = mcΔθ
what does θ represent in the specific heat capacity equation
Temperature change (K)
Why do different materials have different specific heat capacities?
Due to differences in their molecular structure.
Why is copper a good conductor of heat?
Because it has a low specific heat capacity, allowing it to heat up and cool down quickly.
Why is water ideal for heating homes?
It has a high specific heat capacity, meaning it retains heat for a long time.
What happens to energy when a substance changes state?
Energy is required, but there is no change in temperature.
What is latent heat?
The thermal energy required to change the state of one kilogram of a substance without changing its temperature.
What are the two types of latent heat?
Specific latent heat of fusion (melting) and specific latent heat of vaporisation (boiling).
What is the specific latent heat of fusion?
The energy required to convert one kilogram of solid to liquid with no temperature change.
What is the specific latent heat of vaporisation?
The energy required to convert one kilogram of liquid to gas with no temperature change.
What is the equation for calculating latent heat?
Amount of energy needed to change state=latent heat of fusion or vaporisation * change in mass
Why does vaporising water require more energy than melting ice?
Because breaking all inter-molecular forces in boiling requires much more energy than just increasing molecular separation in melting.
What are the two forms of energy?
Kinetic energy and potential energy.
How do kinetic and potential energy relate to molecules?
Kinetic energy is due to the speed of molecules and determines temperature, while potential energy is due to molecular separation and position.
What determines the amount of kinetic and potential energy a substance has?
Its phase of matter (solid, liquid, or gas).
How is internal energy defined?
The sum of the kinetic and potential energies of all molecules within a given mass of a substance.
Which phase of matter has the highest internal energy? Which has the lowest?
Gases have the highest internal energy, while solids have the lowest.
What is absolute zero?
The lowest possible temperature, equal to 0 K or -273.15°C, where molecules have zero kinetic energy.
Can a temperature be lower than 0 K?
No, it is not possible to have a temperature lower than absolute zero, meaning Kelvin temperatures are never negative.
What happens to molecules at absolute zero?
They have zero kinetic energy, meaning no more energy can be removed from the system.
How does kinetic energy relate to temperature in different states of matter?
In solids, molecules vibrate; in gases, they move quickly around their container.
Has absolute zero ever been reached?
No, it remains a theoretical point that has never been achieved in a laboratory.
What does the kinetic theory of gases describe?
It models the thermodynamic behavior of gases by linking microscopic properties (mass and speed) to macroscopic properties (pressure and volume).
What are the key assumptions of the kinetic theory of gases?
- Gas molecules are identical, hard,
- perfectly elastic spheres
- with negligible volume,
- no intermolecular forces,
- and are in continuous random motion.
Why is the volume of gas molecules considered negligible?
Because the size of the molecules is extremely small compared to the total volume of the container.
Why are intermolecular forces ignored in the kinetic theory of gases?
The theory assumes there are no forces of attraction or repulsion between gas molecules.
What is mean square speed in the context of gases?
The mean square speed, <c²>, is the average of the squared velocities of gas molecules and has units of m²/s².
Why do we square the velocities when calculating mean square speed?
Because velocity is a vector, squaring ensures all values are positive, preventing them from canceling out.
What is the root-mean-square (r.m.s) speed?
It is the square root of the mean square speed, representing the average speed of gas particles.
When pressure is high, is volume high or low
low
Relationship between 2 gasses and 2 volumes
P1V1=P2V2
Is volume directly proportional to temp
yes
Is pressure directly proportional to temp
Yes
What is black body radiation?
The thermal radiation emitted by all objects in the form of electromagnetic waves.
In which part of the spectrum does black body radiation usually lie?
Mostly in the infrared region, but it can also include visible light or other wavelengths depending on temperature.
How does temperature affect black body radiation?
Hotter objects emit more infrared radiation in a given time and at shorter wavelengths.
What is a perfect black body?
An object that absorbs (or emits) all radiation incident on it and does not reflect or transmit any radiation.
Why does a perfect black body appear black?
It absorbs all visible light, meaning no colors are reflected back to the observer.
How does temperature affect the black body radiation curve?
As temperature increases, the peak of the curve moves to shorter wavelengths.
What kind of electromagnetic waves have the highest energy?
Waves with shorter wavelengths, such as UV rays and X-rays.
What is the best real-world approximation of a black body?
Stars, as they emit radiation according to their temperature.
What is Stefan-Boltzmann Law
The total energy emitted by a black body per unit area per second is proportional to the fourth power of the absolute temperature of the body
What does Stefan-Boltzmann Law mean
Luminosity is directly proportional to the surface area of a star * Surface temp of the star to the 4th power
What is luminosity sometimes called
PowerW
What is Wien’s law
The black body radiation curve for different temperatures peaks at a wavelength that is inversely proportional to the temperature
What is the equation linked to Wien’s law
llamda max is inversely proportional to temperature
What does Wien’s law tell us when temp is higher
- At peak intensity, wavelength is lower
- Greater intensity of radiation at each wavelength
What colour do hot stars appear as, and why
White/blue, as wavelength is lower when temp increases
