Chapter 3 - Thermal Physics Flashcards
What direction does thermal energy naturally flow in?
Flows from hot to cold.
The temperature difference between two objects in thermal contact will determine the direction of the thermal energy transfer.
What is thermal equilibrium?
When two objects are placed in thermal contact they are expected to reach the same temperature.
How to convert between Kelvins and Celsius, and what zero Kelvin means
T (K) = t (Celsius) + 273
Zero Kelvin is absolute zero where particles have no energy left. However this is impossible in reality because the particles would have to be in a vacuum.
What is pressure in terms of gases, the equation and the units.
Pressure is the force per unit area from the gas acting 90 degrees on the container wall.
p = F/A
A = surface area
Units: Nm^-2 or Pa
How to investigate how quantities are interrelated.
One quantity to be the independent variable, one to be the dependant and another to be the control
Macroscopic point of view
Considers the system as a whole and how it interacts with the surroundings.
Microscopic point of view
Looks inside the system on how the components interact with each other.
How the particles act in terms of the kinetic theory and kinetic energy.
The particles are constantly in random motion and therefore have kinetic energy.
They can have translational kinetic energy ( whole molecule moving in a direction) or rotational kinetic energy (molecule is rotating about one or more axis)
Why do particles have potential energy?
Because of the intermolecular energy between the particles.
What is internal energy?
The total energy the particles have and when a substance is heated we increase its internal energy.
Characteristics of a solid.
Fixed volume and shape, held in position by bonds.
The molecules vibrate around a mean position. The higher the temperature the greater the vibrations.
Characteristics of a liquid.
Fixed volume but can change shape.
The molecules vibrate but not completely fixed in position
Still Strong forces between molecules
Characteristics of a gas.
They will always expand to fill the container
Forces between molecules are weak and they are essentially independent of one another
Occasionally collide
Connection between heat and work
Work is done on a microscopic level - we say heating is taking place. The energy transferred from the heat can increase the K.E or/ and the Potential energy of the particles.
What three things does increases the temperature depend on?
Energy given to the object
The mass
The substance it’s made from
What is Thermal capacity?
The energy required to raise its temperature by 1K
What is Specific heat capacity
The energy required to raise a unit mass of a substance by 1K
What happens when an object is raised above room temperature.
It starts to lose energy until the surrounding temperature is the same as the objects. The hotter it becomes the greater the rate at which loses energy.
Equation for the specific heat capacity in an circuit.
c = (Ix t x V) / m ( T2 - T1)
What occurs when there are two different mixtures at different temperatures?
Energy lost by hot substance cooling down = energy gained by cold substance heating up
Ma x Ca (Ta - Tmax) = Mb x Cb (Tmax - Tb)
What is the universal constant and what is the equation for it?
Universal constant = molar gas constant = R
Units for R: J mol^-1 K^-1
pV/ nT = R
What is an ideal gas?
A gas that follows the gas laws for all the values of p, V, and T
Thus is cannot be liquefied.
What is molar mass and what’s its equation?
It’s the mass of one mole of a substance
No. of moles = number of atoms/ Avogadro constant
When can real gases approximate to ideal behaviour?
The intermolecular forces are small enough to ignore, therefore the pressure/ density of the gas must be low with moderate temperature.
What is Boltzmann’s constant and the equation for it?
It’s a constant ( the actual value is in the booklet)
It’s the idea that absolute temperature is proportional to kinetic energy of a gas molecule.
What are the assumptions of the kinetic model of an ideal gas?
1). Newton’s laws apply to the molecules.
In collisions:
It’s the only time there are intermolecular forces
They are elastic
No time spent
Molecules are treated like points and are in random motion.
What happens to a molecules momentum once it bounces off a wall?
It changes due to the change in direction (momentum is a vector)
What effect does the pressure of molecules hitting the wall have, in a microscopic point of view?
The average of all the microscopic forces on the wall over a period of time means there’s a constant force on the wall.
What’s the pressure law?
At a constant volume, the pressure of a gas is proportional to the temperature.
More kinetic energy means a greater change in momentum when they hit the wall, thus a bigger force.
What is Charles’s law?
At a constant pressure, the volume of a gas is proportional to its temperature in Kelvins.
If the volume of a gas increases, the rate of collisions must go down so the average force on the wall (pressure) remains constant.
What is Boyle’s Law?
At a constant temperature, the pressure of a gas is inversely proportional to its volume.
Constant temperature means constant kinetic energy (speed) of the molecules.
Increase the volume will decrease the pressure
Decrease the volume will increase the pressure
What happens to the temperature when a substance changes phase, and therefore the energy?
It remains constant even though thermal energy is still being transferred. Thus kinetic energy doesn’t increase, so the potential energy increases instead, as bonds are being broken which takes energy, or bonds are being made which releases energy.
What is latent heat?
It’s the amount of energy associated with the phase change
What’s it called when a solid changes to a liquid?
Fusion
What’s it called when a liquid changes into a gas?
Vaporisation
What is specific latent heat and its unit?
The amount of energy per unit mass absorbed or released during a change of phase
Unit: J kg^-1
What would happen in an ideal situation of no energy loss?
A constant rate of energy transfer thus a constant rate of increase of temperature until the point of a phase change.
What’s the difference between the specific heat capacity of a liquid than a solid?
The specific heat capacity of a liquid is less than a solid. A given amount of energy will cause a greater increase in the temperature for the liquid than the solid.
An experiment and equation of measuring the specific heat capacity of fusion of water
Ice is added to warm water and the temperature of the mix is measure.
If no energy is lost from the system:
Energy lost by the water cooling down = the energy gained by the ice
M(w) x c(w) (Tw - Tmix) = M(ice) x L(fusion) + M(i) x c(w) x T(mix)
