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Molecules & Matter (Internal energy (Explanation Kettle on, water…
Molecules &
Matter
Density
Density comparisons
Concrete post heavier than wooden post
Even if they're the same size
Density:
Concrete (2400 kg/m3) > Wood (800 kg/m3)
Density of a substance is its mass
per unit volume
ρ = m/v
Measuring density of solids
Use electronic balance ("0" before measure)
Volume = width x length x height
(Measure - mm ruler, vernier caliper, μ.meter
Irregular solid - dip into water in m.cylinder
Workout volume from rise in water
Measuring density of liquid
Use m.cylinder for volume
Mass = Total - measure equipment (beaker)
States
of matter
The three states
Anything is solid/liquid/gas
Solid -
fixed shape, volume
Liquid -
flow shape, fixed volume
Gas -
flow, fills container, flow volume
(Solid, Liquid density higher than Gas)
Change of state
Physical change (no new substance)
Substance
can regain
origin properties
Can change through
heating/cooling
Examples
Water in kettle, boils, steam - gaseous
Solid CO2, warms up, gas, sublimation
Steam, cold surface, condense, water
Conservation of mass
Substance changes state
No. of particles
in substance - same
Mass of substance is same after change
Example
Mass of ice melts, water has
same mass
Water boils, Steam mass - same
(Even if gas has left container)
Kinetic theory of matter
Particle move increase w/ Temp
Solid
Particles
fixed
together,
Keeps shape;
vibrate
about positions
Liquid
Particles in contact move at random
Gas
Particles move
faster than liquid
Avr. distance
of particles also
bigger
Density is much less than solid/liquid
KE
States have diff. amount of energy
Most energetic in gas; least in solid
Changes of state
Melting & Boiling
H2O - Boil,100°C; Melt,0°C
Pure substance state change:
Temp the same, during change
Freezing, Melting
point the same
Boiling,Condense
point the same
Affected by impurities in substance
Salt water - lower melt point
Energy & change of state
Ice increase temp until 0°C (melts)
Stays constant until all ice melts
Increase to 100°C, water boils
Constant until all water boils
Latent heat
Energy transfer
during state change
It's hidden -
no temp change
Fusion - aka melt (solids can join)
Evaporation
- Any temp, causes cooling
Only on surface
Boil
- Certain temp, doesn't cool,
throughout liquid
Internal
energy
Explanation
Kettle on, water temp increases
Molecules
move faster w/ temp
Boil
- enough
energy to move
away
from each other -
vapour
Internal energy
- stored by particles
Causes
individ. motion, positions
(M&P)
Sum = Total of KE and PE stores
(Of all particles in substance from M&P)
KE of individ. motion (relative)
Potential.E of positions (relative)
Doesn't include GPE/whole KE
Heating
Changes internal energy
, incr. particle energy
Temp of substance incr./Physical state change
Temp increase
Total particle KE incr.
E = mc ∆ θ
For given mass (m) of SHC (c); energy (E)
needed to raise temperature (∆ θ)
Physical change
Total PE of particles change - latent heat
(Energy transfer to/from substance in change)
Solid particles
3D structure, strong particle force
Attraction, bond particles -
fixed
Particles
vibrate
about avr. position
When heated, particles vibrate more
(Particles' energy store increase)
Enough Heating - it
melts/sublimates
(Energy breaks particles from structure)
Liquid particles
Weaker forces of attraction
(FoA)
Not
strong to hold
rigid structure
FoA stops complete separation
Some can
/have enough energy
Escapees are in gaseous state
Gas particles
FoA - insignificant
;
particles move, hi speed
Collide
w/ other particles, internal container
Pressure on surface = force of particle impact
When
heated, particles gain KE
, faster avr.
Cause pressure incr.
- more frequent collision
More forceful collision
Specific
latent heat
Latent heat of fusion
Energy supplied, needed to break free
Transferred to surrounding in solidification
Specific latent heat of fusion = J/kg
E = m x L(F)
If Energy is transferred to solid at melt
and substance mass melts w/o Temp change
Latent heat of vaporisation
Energy supplied to break free
Transferred to surrounding in condensation
Energy needed to boil 1 kg of substance
(w/o temp change) Unit = J/kg
E = m x L(v)
Gas pressure
& Temperature
In the kitchen
Never heat sealed can food
(explode)
Gas pressure
rise w/ temp (collisions)
Energy transfer,
incr. KE of molecules
Avr. KE increases w/ temp increases
Avr. speed increases. w/ KE
Molecules
hit
container
w/ more force/frequency
Impact = tiny force on surface
Millions/s = steady pressure inside
Gas pressure:
Total force exerted on unit area of surface
Observing random motion
Indvid. molecules too small for naked eye
Observe effect through
smoke particles
(Much bigger than air molecules)
Moves haphazardly, unpredictable
Due to fast air molecules, random impact
Gas pressure
& volume
Volume of gas
Depends on pressure, temperature
Can be
compressed/expanded
Produce
net force at 90°
to container wall
Gas stored in tube, piston pushes
Volume decr. = Pressure incr.
(If done slowly, no Temp change)
Compression
To push piston = Work done
(To overcome pressure of gas in tube)
Energy transferred
to gas through work
Quick
= transfer rate
faster
than loss
(Through heating surroundings)
Slowly
= transfer rate
same
as loss
Therefore
no temp change
Explanation of variation of pressure
(with volume)
For fixed mass, No. of molecules constant
Volume decr = Pressure incr.
Smaller space
for molecules
Less distance for impact
w/ container
More frequent impact
Total impact force per m2 (SA) increases
Boyle's Law
pressure x volume is constant
p x V = constant