3.6.2 - Thermal Physics Flashcards
What are the two ways internal energy of a system can change
By giving the gas heat energy, U will increase (or the gas losing heat to its surroundings)
If the gas does work W, U will increase
What is the total energy of a gas also known as?
the internal energy U
What law do we get from the principle of conservation of energy?
the first law of thermodynamics
What happens when a substance is heated (without changing state)?
the KE of particles increases, and the internal energy increases also
What sort of questions will the first law of thermodynamics (conservation of energy) be like?
Qualitative (no numbers involved)
What is the shape of a temp-time graph when an object is changing state? Why?
it stays flat - the temperature does not change since the heat lost to the environment is creating/ breaking bonds.
What is the number of moles equal to?
mass/ relative atomic (or molecular) mass
what is 1 atmosphere in pascals approx. ?
1000 kPa
what is 1m^3 equal to?
1000 litres
1,000,000 cm^3
What is 0K in celcius?
-273.15 degrees
How do you demonstrate the pressure law?
have a fixed vol. of gas in a (jolly) bulb and heat it up in a water bath.
measure the temperature and the pressure, plot a graph of pressure against temperature
What will the pressure-temperature graph look like?
a straight line and extrapolates to get 0K of -273.15 degrees
How do we demonstrate Charles’ Law?
gas in a syringe in a water bath, heat it up, gas expands so volume gets bigger pressure stays same.
plot graph of volume against temp.
What does the volume-temperature graph look like?
straight line which an extrapolation goes to -273 degrees
How do we demonstrate Boyles’ Law?
fixed mass of gas, compress it with a pump and measure pressure and volume. Leave time between readings to allow temp to stabilise
What does the graph of pressure against volume look like?
curve suggesting inverse relationship - can do pressure against 1/volume to get a straight line
What do we call a gas which obeys Boyle’s law at all times? How does this compare to real gases?
an ideal gas
they obey it generally quite well under most conditions
What do we assume in the ideal gas/ Kelvin scale?
that pV = constant x T
What does the k in pV=NkT stand for?
Boltzmann’s constant
What is work done by an expanding gas equal to?
W = p x change in V (p = constant pressure)
What is kinetic theory?
a mathematical model representing an ideal gas
What is Brownian motion?
Robert Brown 1827 observed pollen grains in water and they displayed random motion; evidence that air is made up of a large number of tiny particles moving randomly and very quickly
What causes gas pressure?
when the particles collide with the walls of the container, there is a change in momentum.
from Newton’s second law, a force is exerted on the wall.
the average force divided by the surface area=pressure
Explain what happens to the gas particles inside a car tyre when it is warmer?
a higher temperature means that the particles have more KE and so are moving faster. the change in momentum per collision will be greater and there will be more collisions per second. the total change in momentum per second will be greater and so the pressure will increase.
