Chapter 6 - Thermal Physics Flashcards
(39 cards)
How do we observe Brownian motion?
- look at smoke through a microscope, see smoke grains move jerkily and erratically.
- result of smaller O2 and N particles knocking them. Due to erratic motion of smoke, it shows that air molecules must too be MOVING and have HAPHAZARD motion.
Pressure = ?
The force exerted per unit area of the surface.
SAS of particles in a solid?
Slow, regular, close
SAS of particles in a liquid?
Medium speed, touching but irregular arrangement and close spacing
SAS of particles in a gas?
Fast, no arrangement, large spacing
Describe change of state as heat is added to a solid.
1) increase in temp of solid
2) no increase briefly due to energy being used to break solid bonds
3) increase in temp of liquid
4) no increase for longer time due to energy being used to break liquid bonds (more to break than solid to liquid so time is longer)
5) increase in temp of gas
Why is water more dense than ice?
The arrangement of water is more compacted than ice, since the regular arrangement of particles in ice creates large gaps between particles.
What energy increases when particles break free of their neighbours?
Their electrical potential energy (EPE).
Describe electrical potential energy against separation graph?
- at low separation, EPE is large negative.
- as it increases, separation does too but at EPE proportional to -1/r
- EPE reaches 0 when the particles are completely separated.
What 4 things happen when a substance (eg. Water) is melting/ boiling (flat part of graph)?
- energy is input
- temperature doesn’t change
- molecules break bonds between each other
- EPE increases
Latent heat of fusion = ?
The energy which must be supplied to cause a substance to melt at a constant temperature.
Latent heat of vaporisation = ?
The energy which must be supplied to cause a substance to boil at a constant temperature.
Evaporation = ?
The process by which a liquid becomes a gas at a temperature below its boiling point.
What is formed due to evaporation?
Vapour.
Why does evaporation happen?
- in a liquid particles move about
- some move fast enough to break away from the liquid completely
- some return by chance
- but the result is a net outflow of molecules so eventually a liquid will evaporate completely
Why does the temperature of the liquid fall when it evaporates?
Evaporation occurs due to the particles with the highest KE escaping the liquid. This leads to a lower average KE. Since KE is directly proportion to temperature, a fall in average KE leads to a fall in temperature.
What is the kinetic model?
- matter is made of tiny particles
- they move about
- their important characteristics are MOTION, ORDERING and SPACING of atoms
Why doesn’t water all boil away instantly at 100 degrees Celsius?
Because it takes time for energy to build up enough to break all the bonds.
Define internal energy?
The internal energy of a system is the sum of the random distribution of kinetic and potential energies of its atoms or molecules.
Two ways to change internal energy?
Heat it or compress it (do work on it)
Explain how thermometers work?
- energy is transferred from a hotter object to a cooler one (from substance to thermometer)
- at equal temperatures, two objects will not transfer energy to each other
- when the thermometer is equal temperature to the substance, the reading on it will be the temperature of the thermometer
Define thermal energy?
Energy transferred from on object to another because of a temperature difference.
Define thermal equilibrium?
A condition when two or more objects in contact have the same temperature so that there is no net flow of energy between them.
How does the Celsius scale work?
Takes boiling and melting point of water, divides range into 100 equal intervals, each one is one degree.
