past paper notes- thermodynamics Flashcards
volume of one gas molecule= volume of gas/ number of molecules
mean distance=cube root, volume of one gas molecule
Suggest suitable type of thermometer, one in each case to measure.
(i) the temperature of the flame of a bunsen burner- thermocouple
(ii) the change in temperature of a small crystal when it is exposed to a pulse of ultrasound energy- thermocouple
the specific latent heat of vaporisation is much greater than specific latent heat of fusion for the same substance.
explain this, in terms of spacing of molecules. /1
greater spacing of molecules in vaporisation than in fusion
Explain how movement of the gas molecules cause pressure on the container? /3
gas molecules move in random motion
they collide with each other and the walls of container
this causes change in momentum
force on molecule so force on wall
many forces act over surface area of container exerting a pressure
thermal energy transferred to surroundings means H
so formula can be:
Q=Lm
Q= VIT
VIT= Lm + H
During melting, a solid becomes liquid with little or no change in volume.
Use kinetic theory to explain why during melting process, thermal energy is required although there is no change in temperature? /3
Thermal energy is required to break bonds between particles at constant temperature
potential energy is increases
little work done so required input of energy is thermal
State what may be deduced from the difference in temperatures of two objects? /1
direction of transfer of thermal energy
state the basic principle by which temperature is measured? /1
uses a property that changes with temperature
Explain why the internal energy of the gas is equal to the kinetic energy of the molecules. /2
internal energy= ke + pe
pe is 0 as there is no intermolecular forces
so internal energy = ke
Explain why for an ideal gas, the change in internal energy is directly proportional to the change in thermodynamic temperature of the gas. /3
the potential energy of an ideal gas is zero as there is no imf
internal energy is solely kinetic energy of particles
kinetic energy is proportional to the thermodynamic temperature
equation 1: pV=Nmv^2
equation 2: P=1/3xpx<c^2>
Explain how each of the following terms in equation 2 is derived from equation 1? /4
1) p = Nm/V
2) 1/3= molecules move in 3 dimensions so 1/3 in any direction
3) <c^2> = molecules of different speed so take average of speed^2
Describe the motion of molecules in a gas, according to the kinetic theory of gases. /2
motion of gas molecules is random and constant volume
