Thermal Physics Flashcards
What is meant by Avogadro constant Na?
-number of atoms of carbon-12
-in 0.012kg of carbon-12
What is meant by a mole?
-amount of substance
-containing the same number of particles as in 0.012kg of carbon-12
What is meant by internal energy of a substance?
-sum of kinetic and potential energy of atoms/molecules
-due to random motion
What is meant by specific latent heat?
-(thermal) energy required to change the state of a substance per unit mass
-without any change of temperature
Define specific latent heat of fusion
-(thermal) energy/ heat required to convert unit mass of solid to liquid
-at its normal melting point/ without any change in temperature
Explain qualitatively how molecular movement causes the pressure exerted by a gas
-molecule(s) rebound from wall of vessel/hits wall
-change in momentum gives rise to impulse/ force
-either many impulses averaged to give constant force/ pressure
-or the molecules are in random motion
Use kinetic theory of matter to explain why melting requires energy but there is no change in temperature
-while melting, bonds between molecules are broken/ weakened
-or molecules further apart/ are able to slide over one another
-kinetic energy unchanged so no temperature change
-potential energy increased/ changed so energy required
What is meant by an ideal gas?
-obeys the law pV= constant x T
-at all the values of p, V and T
State and explain the first law of thermodynamics
-Increase in internal energy is equal to heat supplied plus the mechanical work done on it
š„U = q + w
A students state (quite wrongly) that temperature measures the amount of thermal energy(heat) in a body
Give 2 observations with explanation why this statement is wrong
-2 objects of different masses at same temperature
-same material would have different masses at same temperature
-temperature shows direction of heat transfer from high to low regardless of objects
-when substance melts/boils
-heat input but no temperature change
Basic assumptions of kinetic theory of gases
-atoms/ molecules/ particles behave as identical elastic spheres
-volume of atoms/ molecules negligible compared to volume of containing vessel
-no forces of attraction or repulsion between atoms/ molecules
-time of collision negligible to time between collisions
-atoms/ molecules/ particles are in continuous random motion
Describe the motion of molecules in a gas, according to the kinetic theory of gases
-random
-constant velocity or speed in a straight line between collisions
or distribution of speeds/ different directions
By reference to intermolecular forces, explain why the change in internal energy of an ideal gas is equal to the change in total kinetic energy of its molecules
-in ideal gas, no intermolecular forces
-no potential energy
-so change in kinetic energy is change in internal energy
State and explain the change, if any, in the internal energy of a solid metal ball as it falls under gravity in a vacuum
-(random) potential energy of molecules does not change
-(random) kinetic energy of molecules does not change
-so internal energy does not change
By reference to the first law of thermodynamics, state and explain the change, if any, in the interval energy of a lump of solid lead as it melts at constant temperature
-little/ no change in volume
-little/ no external work done
-thermal energy supplied to provide latent heat
-internal energy increases
