16-22;U/Specific Heat/Phase/Evaporation/Heat transer

Question 1

internal energy

Answer 1

total energy of all particles within an object, sum of kinetic energy and potential energy of molecules

Question 2

absolute temp

Answer 2

condition under which molecular motion ceases, 273K, 0 C

Question 3

temp

Answer 3

measure of avg kinetic energy per particle

Question 4

difference between internal energy and temp

Answer 4

two objects of the same temp doesn’t have the same amount of internal energy per gram, temp is not directly proportional to internal energy

Question 5

thermal equil

Answer 5

2 objects at the same temp, no transfer of internal energy between them

Question 6

heating

Answer 6

transfer of energy from a high-temp object to low temp object

Question 7

temp scale

Answer 7

to define reproducible temp scale, should be at least 2 standard reference points to calibrate thermometer: freezing/boiling point

Question 8

universal standard for temp scales is

Answer 8

760mmHg standard Patm

Question 9

fp and bp of water at standard pressure

Answer 9

fp=0 degree Celsius

bp=100 degree Celsius

Question 10

heat

Answer 10

internal energy in transit

Question 11

1st law of TD

Answer 11

dU=Q+W
Q=transfer of heat, microscopic process
W=work done on the system, macroscopic process

conservation of energy

Question 12

thermal expansion

Answer 12

creates destructive stress when bottom of glass vessel is heated so will crack due to large forces that break brittle glass

Question 13

conditions for temp measurements

Answer 13

precise and reproducible manner

Question 14

liquid expansion thermometers

Answer 14

expansion is proportional to temp = height of column in capillary can be calibrated in degrees C or F EG. mercury filled clinical thermometers

Question 15

bi-metallic strip thermometers

Answer 15

2 metals A+B w/ different thermal expansion coefficients bonded together used to measure temp

EG. oven thermometers and thermostats, as they can tolerate wide range of temps

Question 16

constant vol gas thermometer

Answer 16

when V constant = P of enclosed gas directly proportional to Kelvin T

easy to calibrate but large compared to liquid in glass thermometers

Question 17

heat capacity

Answer 17

quantity of heat needed to raise its temp by 1 degree C

high heat capacity = warm up more slowly = absorb greater amount of heat, also cool more slowly = give off more heat

Question 18

specific heat capacity

Answer 18

amount of heat in cal required to raise temp of 1g of substance by 1 degree C

Question 19

dietary calorie

Answer 19

kilocalorie, used to specify energy value of food

used since using food is an oxidation process which is similar to burning in terms of chemical energy released

Question 20

mechanical equivalent of heat

Answer 20

1 cal, 4.186 J

Question 21

heat of combustion

Answer 21

amount of heat released during combustion of a specified amount

Question 22

calorimeter

Answer 22

composed of oxidation chamber surrounded by measured vol of water = when food completely burned = heat of combustion is given to water = energy given off = energy gained by calorimeter = energy of combustion

Question 23

problems with calorimeter

Answer 23

proteins are not completely oxidised by body, energy residues are excreted in urine

not all processes of converting food into energy is in form of heat since body also does mechanical work

Question 24

change of phase means

Answer 24

giving internal energy to a solid body not at melting T

increasing Ek of molecules = weakens bonds = thermal expansion

if enough U added then bonding forces can breaks = frees molecules from rigid positions = melting

Question 25

how to change phase liquid to gas

Answer 25

continuously adding Q to liquid after solid-liquid phase = gradually raises temp to BP = enough U will completely overcome attractive forces = change to gas occurs rapidly

540 cal/g required to convert water to steam at 100 degrees C

Question 26

latent heat of fusion

Answer 26

energy required to melt 1g of solid once it has reached melting temp

Question 27

refrigeration cycle

Answer 27

expansion valve at beginning of cooling coils force refrigerant liquid to evaporate using Bernoulli effect to lower P via boiling to gas = cooling coils will prevent vaporisation = cools interior = energy carried out to compressor = increases P = forces condensation of refrigerant = gives of latent heat of vaporisation = large amount of U = efficient method for cooling

Question 28

how does body cool

Answer 28

via perspiration evaporating = extracts latent heat of vaporisation

Question 29

when does evaporation occur

Answer 29

at T > 0 since higher Ek more molecules escape from liquid into air

Question 30

what increases evaporation rate

Answer 30

increasing T of liquid = more molecules have energy necessary to escape

Question 31

saturation vapour pressure

Answer 31

when vapour is saturated and P exerted on container walls

Question 32

saturation vapor density

Answer 32

mass of water vapour per unit vol under saturation condition

Question 33

relative humidity

Answer 33

% of saturation humidity at given temp

body membranes tend to be sensitive to relative humidity than absolute humidity

Question 34

dew point

Answer 34

temp at which moisture content present in air will saturate air

Question 35

heat transfer

Answer 35

via conduction, convection and radiation of heat

Question 36

conduction

Answer 36

primary method of heat transfer, transfer of heat by direct interaction of molecules in hot area w/ molecules in cooler area via collisions between molecules

efficiency depends on no. of collisions, amount of energy transferred during each collision

Question 37

why are metals generally better heat conductors than nonmetals

Answer 37

free e- in metals move at high speeds = transfer energy by collisions with other e- and with atoms in the metal lattice

Gases are poorer heat conductors = smaller no of molecular collisions in gaseous state

Question 38

explain Fourier’s law

Answer 38

doubling thickness of material = 1/2 rate of heat loss

Question 39

convection

Answer 39

heat transfer by movement of fluid

Question 40

convection current

Answer 40

movement of fluid that carries heat

air rises in T = expands = less dense than surrounding air = buoyant force causes it to rise = more dense cool air moves down to replace it

EG. radiator

Question 41

radiation

Answer 41

energy that comes from a source and travels through space, can penetrate some materials

Question 42

black body

Answer 42

ideal emitter - absorber to absorb all incident light