5.1 Thermal Physics Flashcards
Thermal Equilibrium
When both objects have the same average kinetic energy
Absolute scale of temperature
It’s the thermodynamic scale, and it does not depend on the properties of any particular substance.
How to change from kelvin to Celsius?
add 273 to the Celsius to turn to kelvin
What is Brownian Motion?
Gas molecules move in random haphazard motion
How do you observe Brownian motion in a lab?
- Put smoke in a brightly illuminated glass jar and observe particles using microscope
- Smoke particles appear as bright specs moving haphazardly from side to side
What is internal energy?
Sum of the random distribution of kinetic energy + potential energy of particles in a system
What is absolute zero?
Lowest limit for temperature
Temperature at which a substance has minimum internal energy
What happens as temperature rises?
Increase in internal energy of a body
What happens when a substance changes phase in terms of energy?
Its internal energy changes but kinetic energy remains same so temperature stays the same. Internal Potential energy increases.
Define specific heat capacity
Amount of energy needed to raise the temperature of 1Kg of the substance by 1K
Describe an electrical experiment to determine the specific heat capacity of a metal or liquid?
- Heat substance with heater (need temp rise of 10k to get accurate C)
- With ammeter and voltmeter attached to heater use E=W=VIt
Equipment:
- electric heater
- solid (metalcylindar) or liquid
- insulating material (like np) and lid
- Digital thermometer
Define Specific latent heat of fusion or vaporization
The quantity of thermal energy required to change state of 1kg of a substance
Describe an experiment to determine SLH of a solid or liquid
For a solid:
- Put a heating coil and equal masses of ice in two funnels above beakers
- Turn on one heating coil for 3 minutes. Record the energy transferred in the 3 minutes. Don’t turn on other coil-it’s there so you can measure how much ice melts due to the ambient temperature of the room
- At the end of the 3 minutes, measure mass of the water collected in the beaker. Subtract one form the other to get the mass of ice, m, that melted solely due to the presence of the heater.
- E=mL, so to find the SLH of fusion for water, L=E/m
For a liquid- boil water in a distilling flask, condense the vapour given off and E/m of condensed water collected
Describe a solid in terms of spacing, ordering and motion
-The molecules are arranged in a
regular, 3-dimensional structure.
- The atoms and molecules are bonded to each other by strong, attractive forces due to the electrical charges of the electrons and protons in the atoms.
- The molecules are relatively close to each other (~ 3.0 x 10^-10 m) and vibrate about fixed positions. The higher the temperature of the solid, the greater is the amplitude of vibration of the molecules.
Describe a liquid in terms of spacing, ordering and motion
- The molecules are still in contact and vibrating, but they are free to move around randomly and this is why a liquid flows and has no fixed shape.
- The attractive forces between the molecules are weaker than in a solid and not strong enough to hold them in fixed positions.
- The separation of the molecules is about the same as it is in solids (~ 3.0 x 10^-10 m)
Describe a gas in terms of spacing, ordering and motion
- The intermolecular forces are negligible and so the molecules are completely free of each other. They whiz around in rapid, random motion, colliding with the walls of the containing vessel and with each other. It is this molecular bombardment of the container walls which gives rise to gas pressure.
- On average, the molecules are about ten times further apart (~ 3.0 x 10^-9 m) than they are in solids and liquids. This is why a gas occupies a much larger volume than the same mass of liquid.
State how the observations from smoke experiemnt lead to conclusions about the nature and properties of the molecules of a gas
- movement of smoke particles caused by (being hit by) randomly moving air molecules
- smoke particles are continuously moving because the air molecules are continuously moving
- smoke particles are visible but air molecules are not hence air molecules must be (very) small.
- small movement of smoke particles is due to the large numbers of air molecules hitting from all sides
What is a mole?
One mole is the amount of substance containing 6.02×10^23 particles
What are the 4 assumptions for the model of kinetic theory of gases?
large number of molecules in random, rapid motion
particles (atoms or molecules) occupy negligible
volume compared to the volume of gas
all collisions are perfectly elastic and the time of
the collisions is negligible compared to the time
between collisions
negligible forces between particles except during
collision
Explain how The kinetic theory of gases can be used to understand how gas in a container produces pressure.
As the collisions between atoms and the wall of the container are perfectly elastic, the atoms rebound from the wall at the same speed they travel in at.
This makes their change in momentum, p, (given by p = m(v-u)) equal to 2mv. As the change in momentum is equal to force multiplied by time, the average force exerted on the atom by the wall is given by 𝐹=2mv/2
Using Newton’s third law, the atom also exerts an equal and opposite force on the wall of the container. The total pressure on the wall is equal to the sum of the force of each collision between atoms in the gas and the wall, and the area of the wall.
Explain how the internal energy of an ideal gas is related to its temperature.
Ideal gas has Zero potential energy,
Ke is proportional to T.
State Boyle’s law
pV=constant
State pressure law
p/T=constant
State Charles’ Law
At constant pressure Volume of gas is directly proportional to absolute temperature
How do you investigate Boyles law?
- Oil confines parcel of air in sealed tube with fixed dimensions
- Tyre pump increases pressure, Bourdon gauge records the pressure.
- Volume will decrease as air compresses
- Not down pressure and volume of air
How do you investigate pressure law
- Immerse flask of air in beaker of water (submerge as much as possible)
- Connect stopper to bourdon gauge using short tube (volume of tube much smaller then flask)
- Record pressure and temp
- Heat water, then remove heat (stir for uniform temperature, allow time for heat to transfer to air)
- Record pressure and temperature
- heat again and repeat till bp reached
- Repeat twice all over again (with fresh water)
- plot P against T, LOBF, estimate absolute zero by extrapolation up to x axis
