Thermal Physics Flashcards
What is temperature
The measure of hotness of an object
What is The triple point?
The specific temperature and pressure where solid, liquid, and gas phases coexist in thermal equilibrium. No net transfer of thermal energy between phases.
What is the Zeroth Law
If two objects are each in thermal equilibrium
with a third, then all three are in thermal equilibrium with each other.
What is Absolute Temperature
Absolute temperature scale uses water’s triple point and absolute zero; measured in kelvin (K), with increments equal to Celsius. Relationship: Kelvin = Celsius + 273. Kelvins are positive, with 0K as the lowest temperature.
Describe the arrangements of solids
Atoms are closely packed together. Strong electrostatic forces of attraction between molecules. Molecules have kinetic energy, which allows them to vibrate around their fixed positions.
Describe the arrangements of liquids
Molecules have a greater mean separation between each other than in solids. Molecules have more kinetic energy than solids, enabling them to change position and flow past each other.
Describe the arrangements of gases
Molecules have greater kinetic energy than in liquids, are farther apart, and move randomly with negligible forces between them, only interacting upon collision.
What is brownian motion
The molecules of a gas travel in random directions with random velocity. Can be seen by looking at smoke particles in air. The smoke particles are visible under a microscope, and exhibit random motion because of their collisions with the molecules in air, which result in a transfer of momentum in random ways.
Why does volume increase as temperature increases
At higher temperatures, the average speed of particles increase. This increases the rate of collisions causing the substance to expand.
What is the formula to calculate the spacing between molecules in a volume of a substance
Spacing = (Volume / Number of molecules) to the power 1 third.
Define Internal energy
The sum of the randomly distributed kinetic and potential energies of atoms or molecules within the substance.
How is internal energy increased?
Raising temperature increases internal energy and average kinetic energy of atoms or molecules. Phase changes, increase electrostatic potential energy.
What happens during phase changes
During phase changes like melting or boiling, energy transfer increases electrostatic potential energy without raising temperature. Once the phase change completes, temperature rises as kinetic energy increases.
What are the characteristics of a Temperature-Time graph
Temperature on Y axis
Time on X - Axis
Specific heat capacity calculated by Power / Mass * Gradient
How to determine the specific heat capacity of a solid or liquid
Using a digital scale, measure the mass of the solid or liquid. Connect an electrical heater to a power supply, ammeter, switch and variable resistor in series. Connect a voltmeter to the electrical heater in parallel. Insulate the solid or liquid and place a thermometer to find its initial temperature. Place the heater in the solid or liquid and turn the switch on. Time how long the solid or liquid takes to increase in temperature by 10 degrees. Stir liquid to make temperature uniform. Calculate specific heat capacity using equation C = Current * velocity of heater * time taken / mass * 10.
What is electrostatic potential energy?
Electrostatic potential energy relates to attractive or repulsive forces between charged particles. Negative values indicate attractive forces, requiring energy to separate particles. As distance between particles increases, it becomes less negative, reaching zero at infinite separation.
What is specific heat capacity
Energy needed per unit mass to change temperature by 1K (or 1°C), with units Jkg-1 K-1.
What is Specific Latent heat of fusion
The energy required per unit mass of a substance to change from solid to a liquid.
What is Specific latent heat of vaporisation
The energy required per unit mass of a substance to change from liquid to a gas.
Why Is it not possible to go lower than 0k
At 0k, the internal energy of a substance is at its minimum. The kinetic energy of all molecules are 0 and have stopped moving.
Why is Latent heat of vaporisation usually higher than latent heat of fusion
There is a bigger difference in internal energy between a liquid and gas than between a solid and liquid.
What is Molar Mass
The mass of one mole of a substance. The nucleon number of an element is the mass of one mole of that element in grams. Number of moles = Mass / Nucleon Number
What are the assumptions of an Ideal gas
1) The gas has a large amount of molecules moving in random directions with random speeds
2) The molecules of the gas occupy negligible volume compared to the volume of the gas
3) Collisions between molecules and container walls are elastic
4) The time during collisions between molecules is negligible compared to time between collisions.
5) Electrostatic forces between molecules are negligible except during collisions.
How does gas in a container produce pressure
Collisions between molecules and container walls are perfectly elastic, which means kinetic energy is conserved. Molecules rebound off container wall with the same velocity as before collision but in opposite direction: -v. Therefore the change in momentum is -2mv. Force = Change in momentum / Time during collision, therefore the wall exerts a force of -2mv/t on the molecule. According to newtons 3rd law, the atom also exerts an equal and opposite force on the container wall. Since a large number of atoms collide with the walls, a collective force is exerted on the cross sectional area of the walls, therefore the molecules exert pressure on the walls.
What is boyles law
At a constant temperature, pressure of an ideal gas is inversely proportional to volume.
What is the relationship between Pressure and temperature in an ideal gas
Directly proportional. p1v1/t1 = p2v2/t2
What is the equation of state of an ideal gas
pressure * Volume = number of moles * 8.31 * temperature in kelvin
Characteristics of a Pressure *Volume - Temperature graph
Gradient = number of moles
What is the root mean square speed
Square the value of each speed given, then divide by how many speeds there are. This is the mean square speed - C bar ^2. Square root this value to get root mean square speed.
What is the equation for pressure of a gas at the microscopic level
Pv = 1/3 number of molecules * mass of a single molecule * mean square speed
What are the characteristics of the Max Boltzmann distribution
Particles in a gas move randomly, with velocities varying widely. The area under the graph represents the total number of molecules. As the gas temperature increases, the peak shifts to a higher speed and the distribution broadens.
What is the boltsmann constant equation
Pressure * Volume = Number of molecules * 1.38 * 10^-23 * Temperature
How to investigate boyles law in an experiment
Fill a sealed syringe with gas and connect it to a pressure gauge. Use the syringe to vary the volume of the container, and record the values for volume and pressure. When a graph of pressure against 1/volume is plotted, a straight line should be produced, showing a constant relationship. To increase accuracy in this experiment, the syringe should be lowered slowly so that no heat is produced from friction.
How to estimate absolute 0
A sealed container of air, connected to a pressure
gauge, is placed in a water bath. The temperature of the water is varied, and the values of temperature and pressure and recorded. When pressure is plotted against temperature, a linear graph will be produced. At absolute zero, the gas molecules will have no kinetic energy, so
there will be no collisions with the container walls, resulting in there being no gas pressure. By
extrapolating the graph back the x intercept can be found, and this is equal to absolute 0.
How is mean kinetic energy and temperature of an ideal gas related
The kinetic energy of gas molecules in an ideal gas is proportional to the temperature. Given by the equation 1/2 * mass of molecule * mean square speed.
