Year 2 - A level Flashcards
What are the two parts of internal energy of molecules?
- Potential energy due to electrostatic attraction
- KE due to movement
Why can’t a body possess heat energy?
Heating is energy in transit from hot to cold regions.
Brownian motion
- Jerky, random motion
- Large smoke particles collide randomly with invisible air particles
Diffusion
Spread of gas or liquid in space provided.
What is Boyle’s Law?
For a fixed mass of gas at constant temp. pressure is inversely proportional to its volume.
Explain kinetic theory and pressure.
-Molecules hit container, require force change momentum and rebound.
-Newton 3rd, equal and opposite force on wall.
-Force increases, collisions faster and more frequent. Both increase with speed.
Therfore, KE molecules is directly proportional to temp.
What is Charles’ Law?
For a fixed mass of gas at constant pressure, volume is directly proportional to its absolute (kelvin) temperature.
What is the pressure Law?
For a fixed mass of gas at constant volume, pressure is directly proportional to Kelvin temperature.
What is the equation with p1 v1 and t1?
(P1V1)/T1 = (P2V2)/T2
What unit is temperature measured in?
Kelvin 0K = -273 degrees C
What is the ideal gas equation?
pV = nRT
KE theory 1.
What is change of momentum of particle m,cx as it hits wall x? What is the time between impacts on wall x over distnace L?
- Change in momentum = m(-cx) x mcx = -2mcx.
2. t = 2L/cx - between wall x collisions is two lengths
KE theory 2.
What is the force on the particle? and therefore the wall?
Change in momentum / time = -mcx^2/L
Newton’s 3rd means wall is +mcx^2/L
KE theory 3.
What is the pressure of 1 molecule?
Force / area. mcx^2/L^3 = mcx^2/V
Assuming N molecules what is the equation for pressure?
pV = 1/3Nmc^2 - 1/3 move perpendicular to each side.
As Nm is total mass p = 1/3ρc^2
How do you find (root mean squared speed)?
Square all speeds, find their mean, square root all
What are the 5 assumptions of ideal gases?
- No inter particle forces - All KE
- All collisions with wall perfectly elastic
- Obey Newton’s Laws
- Time during collision is negligible
- Molecules occupy zero volume
What are the ideal gas eqn’s from theory and expt?
Theory: pV =1/3Nmc^2
Expt: pV = nRT
Therefore, RT = 1/3Nmc^2
What is boltzmann’s constant in terms of R and NvA
k = Univ. gas constant / avagadro
What is mean KE of a molecule and therfore a mole?
KE of molecule = 3KT/2 and of a mole 3RT/2
At given temp what do all molecules have?
Same KE.
What links rms speed and temp?
Root of temp is proportional to rms speed.
What is a fixed point?
A point such as the boiling point of water which can be used to calibrate two thermometers.
Why do objects move in a cirlce?
Due to a resultant force acting towards the centre of the circle.