Topic 9: Thermodynamics Flashcards
What is the definition of Internal energy?
Internal energy/heat is the sum of kinetic energy and potential energy for all molecules.
How does internal energy change when a substance changes state?
Internal energy also changes. KE stays the same so heat energy is transferred to potential energy.
What happens when Kinetic/Potential energy of molecules increase?
Kinetic increase
- Molecules move faster
Potential increase
- Particles move further/closer to each other
What is the definition of temperature?
Temperature is the average kinetic energy of the particles in a material.
What is the absolute scale of temperature measured in?
How do you convert from degrees to absolute scale?
Absolute scale of temperature is measured in kelvins.
To get from degrees to kelvin, add 273.15K.
What is absolute zero?
Absolute zero is when temperature is 0 kelvin
Particles have:
-Zero Kinetic energy
-Exert zero pressure
-No volume
What is the specific heat capacity?
Specific heat capacity is
-the amount of energy needed
-to raise temperature of 1kg of a substance
-by 1 kelvin
What is the formula for specific heat capacity?
Change in energy = mass x specific heat capacity x change in temp
How does internal/kinetic energy change during a change in state of a substance?
The internal energy changes but the kinetic energy (and temperature) doesn’t.
This is because the energy is transferred to potential energy to help break the bonds of the particles.
What is specific latent heat?
Specific latent heat is:
-Amount of energy needed
-for 1kg substance
-to change state
What are the two types of specific latent heat and what is the difference?
Specific latent heat of vapourisation —> between gas and liquid
Specific latent heat of fusion —> between solid and liquid
What is the formula for specific latent heat?
energy = mass x latent heat of fusion/vapouristaion
What is an ideal gas?
Ideal gases do not have forces between particle therefore particles have no potential energy, only kinetic energy.
What are the 5 assumptions of ideal gases?
- All molecules act as identical, hard shapes
- V of molecules is negligible compared to V of container
- Time of collision is negligible compared to time between collisions
- No forces of attraction/repulsion between molecules
- Molecules are in continuous random motion
- Collisions are all elastic
What does the gas law of Boyle’s Law state?
For a constant mass of gas at a constant temperature:
- the PRESSURE exerted is INVERSELY proportional to the VOLUME
- P =k x 1/v
What does the gas law of Charles Law state?
For a constant mass at constant pressure:
- The VOLUME occupied is PROPORTIONAL to its ABSOLUTE TEMPERATURE
- V = kT
What does the gas law of Pressure Law state?
For a constant mass and constant volume:
- The PRESSURE exerted by the gas is PROPORTIONAL to the ABSOLUTE TEMPERATURE
- p = kT
What do the gas laws combine to give?
Gas laws can be combined to give equation - pv/T = constant
The constant in the equation depends on the amount of gas present which is equal to Nk
N - number of molecules
K - Boltzmann’s constant 1.38x10^-23
Plugging Nk into the equation gives:
pV/T = Nk
pV = NkT
What is a black body radiator?
A black body radiator is a perfect absorber and emitter; absorbs and emit all frequencies of EM radiation.
What are two laws/formulas used with black-body radiation?
Stefan-Boltzmann Law
L = σAT^4
Wien’s Law
λmax x T = 2.989x10^3 mK
What do all objects with a temperature above absolute zero emit?
Objects above absolute zero emit energy in the form of EM radiation.
What is Lambda max?
The point of Lambda max will be at the wavelength at which it emits the largest intensity of radiation.
What does the wavelength and intensity of radiation depend on?
Both wavelength and intensity depend on temperature of the black body.
What is the relationship between the temperature, intensity and the wavelength?
As the object gets hotter, it emits more short wavelength radiation and intensity of radiation increases
Which objects produce a visible light?
Objects that are very hot
What does Stefan-Boltzmann law state?
Stefan’s Law states that Luminosity ,L of a blackbody radiator (power output) is directly proportional to its surface area (A) and its absolute temperature (T).
L = σAT^4
σ = Stefan-Boltzmann’s constant (5.67x10^-8)
L=4πr^2 x σ x T^4
What does Wien’s displacement law state?
Wien’s law states that peak wavelength of emitted radiation from black body is inversely proportional to its absolute temperature.
What is the formula for Wien’s law?
λmax x T = 2.989x10^3 mK
λmax = max wavelength
T = Temperature in K
mK = meters Kelvin
Explain why pressure increases when the air is heated in a container of fixed volume. (4)
- Increased temp causes increased average KE of molecules
- Molecules have greater speed ; collision rate with walls greater
- Rate of change momentum during collision increases
- Causes greater force to be exerted on wall, increasing pressure
How does heat affect density of air?
- Increased heat means avg KE of air molecules increase
- Creates expansion effect, decreasing density
Explain, using ideas of momentum, why pressure exerted by a gas increases as the temperature of the gas increases.
- As temp increases, avg KE increases
- Greater speed so momentum of atom increases
- Rate of collisions of atoms with container walls increases
- Rate of change of momentum at the walls increases
- Rate of change of momentum is equal to force
- Pressure is F/A and force is greater
