Thermodynamics Flashcards
what is the kinetic model of matter
matter is composed of a large number of small particles that are in constant motion
structure in solids
- atoms are close and held in place by strong intermolecular bonds, which prevent particles from moving hence solid’s rigid shape
- atoms in regular pattern
- atoms vibrate at fixed positions
structure in liquids
- molecules close
- irregular arrangement
- flow is due to molecules having enough energy to break intermolecular bonds and move/slide
structure in a gas
- widely separated in every direction
- move randomly, at high speeds
- no intermolecular forces so atoms freely move
- can be easily compressed due to a lot of space between atoms
why do melting and boiling take place w/out a temp change
- water absorbs energy to melt/boil
- this is used to change state, not temp: bonds are broken
- U=KE+PE, PE is increased to incease spacing (farther objects, more PE to attract)
- KE is constant and since KE is proportional to T, T is constant too (KE is used to move them apart, but is converted to PE)
during vaporisation why is more energy required than during fusion
-energy is needed to completely separate molecules to the point where there are no intermolecular forces acting
during fusion why is less energy required compared to during vaporisation
-energy is needed to separate molecules from rigid arrangement to a free-flowing one, that means intermolecular bonds become weaker but dont completely break
why does cooling accompany evaporation
-as molecules change state energy is removed and hence taken away from surface of liquid as the gas moves away
:to escape, individual molecules must have KE above the average KE. when they do and escape, the average KE liquid molecules decreases and since KE is proportional to T, temp decreases too
define specific heat capacity
amount of thermal energy needed to raise the temperature of 1kg of a substance by 1C
when is more thermal energy needed to raise temp
-heavier the material the more the energy to raise temp
higher the temp change, more energy needed
formula for change in thermal energy, w respect to m temp, and c
Q=mc(01-02)
higher specific heat capacity means that
more energy is needed to change the temp by a bit even cos it takes long to cool and warm up eg water
when are materials good heat conductors
low specific heat capacity
define latent heat
thermal energy required to change the state of 1kg of mass of a substance without any temp change
define latent heat of fusion
thermal energy required to change the state of 1kg of solid to liquid with no temp change
(used for both melting and freezing)
define latent heat of vaporisation
thermal energy required to change the state of 1kg of liquid to gas with no temp change
(used for both vaporising and condensing)
formula for thermal energy in terms of mass and latent heat
Q=mL
why is latent heat of vaporisation more than fusion
- ice melting energy is only needed to increase separation to allow free flowing
- but water boiling energy is needed to completely separate w no forces of attraction
define internal energy
sum of the random distribution of kinetic and potential energies within a system of molecules
what is internal energy determined by
- temp
- random motion of particles
- phase of matter (gas>liquid>solid) cos fastest+farthest means most KE and PE
how to increase internal energy of a system
- do work on it
- add heat to it
how to decrease internal energy of a system
- lose heat to surrounding
- system does work on surrounding
state what solid, liquid, and ideal gas molecules have in terms of KE and PE
- solids and liquids have both KE and PE because they vibrate/slide and are close together and bound by intermolecular forces
- ideal gases have only KE, cos they are considered to have no intermolecular forces therefore no PE
equation that shows that internal energy of an ideal gas is directly proportional to change in temp
U=3/2Nk(T1-T2)
area under a pressure-volume graph represents
work done
a horizontal line on a P-V graph means
a graph of constant pressure
a horizontal line on a P-V graph with an arrow going to the right means x,y,z
and going to the left means x,y,z
to right: volume is increasing (expansion), work is done by the gas, internal energy decreases
to left: volume is decreasing (compression), work is done on the gas, internal energy increases
a vertical line on a P-V graph means
a graph of constant volume
if theres a vertical line with an arrow going up or down on aP-V graph, what does this means for the area under the curve and the work done
area is zero (perpendicular line)
and so no work is done (0) when volume stays the same
work is only done when volume of gas changes. which equation proves this statment
W=P(V2-V1), where P is constant
