the particulate nature of matter Flashcards
Albedo:
the fraction of solar radiation that is reflected back into space by the planet
formula:
(total scattering power)/(total incident power)
Earth’s average albedo
0.3 or 30%
Earth’s albedo varies according to:
- season
- cloud cover
- latitude
- surface conditions
luminosity does not equal
brightness
luminosity equals
power
brightness equals
intensity
what is the greenhouse effect?
- natural process
- without it the Earth temp. would be +- 18 celsius
- greenhouse gases reduce surface radiated heat loss
what are the greenhouse gases?
- Methane, CH4
- Water, H2O
- Carbon dioxide, CO2
- Nitrous Oxide, N2O
What is resonance?
Molecules in greenhouse gases have a natural frequency, outgoing infrared radiation emitted from the earth has the same natural frequency as molecules, causing the molecules to absorb the infrared energy and oscillate at greater amplitudes. The internal energy of the molecules increases and they re-radiate the I.R. energy in all directions, including down
energy levels of molecules
- an electron close to the nucleus can gain a photon of energy and move to an energy level further from the nucleus
- only photons of specific frequency can cause the electron to move
photon
quantum ‘particle’ of energy
Emissivity
power radiated by object/ power radiated by black body of the same size at same temp.
emissivity of atmosphere = radiated by atmosphere
Stefan-Boltzmann law for a black body:
- power radiated by a black body is proportional to surface area of body and kelvin temperature to the power of 4
What are some limitations of simple energy balance climate model?
- solar constant can change due to solar activity
- changes in albedo and emissivity
What affects albedo and emissivity?
- convection currents
- fluid dynamics
- Earth’s spin
What is temperature?
measure of the average kinetic energy of molecules in random motion
What is heat energy?
Energy going from a hotter body to a colder body
Internal energy
Kinetic Energy + Potential Energy
(ideal gases have only kinetic energy as the collisions between walls are elastic, therefore kinetic energy is preserved)
Properties of ideal gases:
- large number of particles (allows statistical averages to be taken)
- volume of each particle is negligible compared to the volume of the container
- no intermolecular forces between particles
- particles move randomly in all directions at high speeds
- collisions between particles and the walls of the container are perfectly elastic - KE is preserved, PE is 0.
- duration of a collision is negligible compared to the time between collisions
Under what conditions is the real gas a good approximation to an ideal gas?
- high temperature (speed of particles is high and duration of collisions is short)
- low pressure
- low density ( volume of particles is negligible compared to that of the whole gas)
What is the first gas law? + equation
Boyle’s Law
- for a fixed number of moles of gas at constant temperature, the pressure of the gas is inversely proportional to its volume. P=1/V
What is the second gas law? + equation
Charles’ law
- for a fixed number of moles of gas at constant pressure, the volume of the gas is directly proportional to its temperature in Kelvin. V/T = constant
What is the third law? + equation
Gay-Lussac’s law
- for a fixed number of moles of gas at constant volume, the pressure of the gas is directly proportional to its temperature in Kelvin. P/T = constant
magic formula combining gas laws
(P1V1)/T1 = (P2V2)/T2
collisions between particles in an ideal gas and the walls
- collisions are elastic, thus magnitude of the particle’s velocity doesn’t change, but the direction changes, therefore change in velocity -> change in momentum
equation relating to the relationship between gas pressure and the av. velocity of its particles
P= 1/3 pvˆ2
What is gas pressure caused by?
caused by the collisions between particles and the walls of their container due to the change in momentum during the collision
What does pressure of a gas depend on?
depends on the density of the particles and their average velocity
explain, with reference to the energy of the molecules, why there is a constant temperature region on the graph (melting of ice, temperature/time)
Latent heat of ice -> energy required to change from solid ice to liquid water.
The heat energy is absorbed to increase potential energy of molecules by weakening bonds and increase molecular separation. The average KE of the molecules is constant therefore the temperature is constant until all the ice has melted
