Karteikarten
Thermodynamics
Karten in diesem Stapel (22)
- 1Define "ideal gas".WJEC: "An ideal gas is one that perfectly obeys the equation pV=nRT, where n is the number of moles, R is the molar gas constant, and T is the Kelvin temperature."
Macroscopically, ideal gas is one that obey's Boyle's law at all temperatures. Microscopically, it is one in which the forces between the molecules can be neglected. - 2Define the mole and Avogadro's constant.The mole is the SI unit of "amount of substance". It is the amount containing as many molecules as there are atoms in 12 grams of carbon-12.
The Avogadro constant is the number of particles per mole. - 3Define "internal energy" (U) of a system.The internal energy is the sum of the kinetic and bond potential energies of all the particles of a system (NB kinetic energy is random kinetic energy; it is independent of the movement of the system as a whole).
- 4What is heat (Q)?Heat is energy flow from a region at higher temperature to a region at lower temperature due to the temperature difference.
- 5Explain what is meant by: 1. Thermal equilibrium 2. Steady state1. A state in which there is no net transfer of energy between parts of the system. All parts of the system are at a constant, equal temperature.
2. A state characterised by constant rate of energy flow. Parts of the system are at constant but unequal temperatures. - 6What is meant by: 1. Isolated system 2. State1. Part of the universe that is prevented from exchanging energy with the rest of the universe.
2. A specific situation in which the system's macroscopic variables have particular values. - 7What is meant by: 1. Isothermal 2. Adiabatic 3. Thermometer1. Change of state occurring at constant temperature
2. Change of state occurring without heating
3. An object that has a physical property that depends on temperature - 8How are the following temperature scales defined? 1. Centigrade 2. Kelvin 3. Celsius1. Dividing the interval between the boiling point and the ice point into 100 equal parts
2. Set triple point at 273.16 K and absolute zero at zero. Then 1 degree kelvin = 1/273.16 of the triple point of water
3. Defined as kelvin temperature minus 273.15 - 9State: 1. Boyle's Law 2. Charles' Law 3. The Pressure Law1. For a system at constant temperature, the pressure is inversely proportional to the volume.
2. For a system at constant pressure, the volume is proportional to the temperature.
3. For a system at constant volume, the pressure is proportional to the temperature. - 10What are the conditions under which Boyle's law holds?1. Temperature is well above that at which the gas starts to condense
2. Pressure is not too high
3. Volume is not too small
4. No gas escapes - 11What is the ideal gas equation?pV=nRT (=NkT)
- 12On what foundational assumptions is the kinetic theory of gases based?1. Gases are made up of spherical molecules that cannot be broken up
2. A very large number of such molecules exist within a small volume of gas
3. The volume of the molecules is very much smaller than the volume of the gas
4. The time between collisions is much greater than the time in collision
5. Collisions are elastic
6. No long range forces act between the molecules - 13What is the result of kinetic theory equivalent to the experimentally derived ideal gas equation?pV = 1/3 Nm
(NB: N is the number of molecules; m is the mass of a single molecule) - 14What is the average kinetic energy of molecules in a gas? Derive this result.= 3/2 kT
- 15Why, for an ideal gas, does the internal energy only depend on temperature?Since there are no long range forces acting in an ideal gas, there is no potential energy to consider. Therefore, the internal energy of a gas = the sum of the kinetic energy of all its molecules. From the above result, this depends only on temperature.
- 16State the formula for the internal energy of an ideal gas.U = 3/2 NkT = 3/2 nRT
- 17If work is done isothermally on a gas, what else must be happening?The gas must be losing energy as heat to the surroundings.
- 18What is the theorem of equipartition of energy?This theorem states that, with a system in thermal equilibrium, any form of energy that depends on some quantity squared will have an average value of 1/2 kT.
- 19What is the Dulong and Petit law?Experimental measures of the molar heat capacities of different substances show them to be remarkably similar. The molar heat capacity of all substances at high enough temperatures is about 25 J/K/mol
- 20What is specific heat capacity?The amount of energy required to raise 1kg of a substance by 1K.
- 21Why does temperature remain constant while matter is undergoing a phase change?Consider molten wax cooling. The wax continues to loose energy to its surroundings at the same rate when it begins to solidify. But as bonds are formed during solidification, energy is released, which holds the wax at constant temperature for a while.
- 22What is latent heat?The amount of energy released or absorbed when a phase change takes place.
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- A level Physics (A level) Karteikarten am Thermodynamics, erstellt von muon neutrino am 19/02/2018.
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