Thermodynamics

Question 1

what is the kinetic model of matter

Answer 1

matter is composed of a large number of small particles that are in constant motion

Question 2

structure in solids

Answer 2

• 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

Question 3

structure in liquids

Answer 3

• molecules close
• irregular arrangement
• flow is due to molecules having enough energy to break intermolecular bonds and move/slide

Question 4

structure in a gas

Answer 4

• 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

Question 5

why do melting and boiling take place w/out a temp change

Answer 5

• 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)

Question 6

during vaporisation why is more energy required than during fusion

Answer 6

-energy is needed to completely separate molecules to the point where there are no intermolecular forces acting

Question 7

during fusion why is less energy required compared to during vaporisation

Answer 7

-energy is needed to separate molecules from rigid arrangement to a free-flowing one, that means intermolecular bonds become weaker but dont completely break

Question 8

why does cooling accompany evaporation

Answer 8

-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

Question 9

define specific heat capacity

Answer 9

amount of thermal energy needed to raise the temperature of 1kg of a substance by 1C

Question 10

when is more thermal energy needed to raise temp

Answer 10

-heavier the material the more the energy to raise temp

higher the temp change, more energy needed

Question 11

formula for change in thermal energy, w respect to m temp, and c

Answer 11

Q=mc(01-02)

Question 12

higher specific heat capacity means that

Answer 12

more energy is needed to change the temp by a bit even cos it takes long to cool and warm up eg water

Question 13

when are materials good heat conductors

Answer 13

low specific heat capacity

Question 14

define latent heat

Answer 14

thermal energy required to change the state of 1kg of mass of a substance without any temp change

Question 15

define latent heat of fusion

Answer 15

thermal energy required to change the state of 1kg of solid to liquid with no temp change
(used for both melting and freezing)

Question 16

define latent heat of vaporisation

Answer 16

thermal energy required to change the state of 1kg of liquid to gas with no temp change
(used for both vaporising and condensing)

Question 17

formula for thermal energy in terms of mass and latent heat

Answer 17

Q=mL

Question 18

why is latent heat of vaporisation more than fusion

Answer 18

• 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

Question 19

define internal energy

Answer 19

sum of the random distribution of kinetic and potential energies within a system of molecules

Question 20

what is internal energy determined by

Answer 20

• temp
• random motion of particles
• phase of matter (gas>liquid>solid) cos fastest+farthest means most KE and PE

Question 21

how to increase internal energy of a system

Answer 21

• do work on it

- add heat to it

Question 22

how to decrease internal energy of a system

Answer 22

• lose heat to surrounding

- system does work on surrounding

Question 23

state what solid, liquid, and ideal gas molecules have in terms of KE and PE

Answer 23

• 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

Question 24

equation that shows that internal energy of an ideal gas is directly proportional to change in temp

Answer 24

U=3/2Nk(T1-T2)

Question 25

area under a pressure-volume graph represents

Answer 25

work done

Question 26

a horizontal line on a P-V graph means

Answer 26

a graph of constant pressure

Question 27

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

Answer 27

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

Question 28

a vertical line on a P-V graph means

Answer 28

a graph of constant volume

Question 29

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

Answer 29

area is zero (perpendicular line)

and so no work is done (0) when volume stays the same

Question 30

work is only done when volume of gas changes. which equation proves this statment

Answer 30

W=P(V2-V1), where P is constant