Chapter 5: States of Matter Flashcards
States of matter are characterized by
Different energies of particles
Kinetic theory of matter:
Energy of particles is directly proportional to the temperature in the Kelvin scale of the system.
State of matter at given temp and pressure is determined by strength of intermolecular force between particles
Properties of particles in solid, liquid, gas states
S: closely packed, inter particle force strong, vibrate in position, fixed shape and volume
L: more spread, force weaker, slide over each other, no fixed shape, fixed volume
G: spread out, force negligible, move freely, no fixed shape and volume
Explain the heating curve:
Solid is heated, vibrational E increases and so does temp. Line going up
Melting point. Vibrations enough energetic for molecules to move away from fixed positions to form liquid. E added at this stage used to break intermolecular force, not raise KE, so temp (line) constant
Liquid heated, KE gained, temp goes up
Boiling point. Enough energy to break all intermolecular forces and form gas. Needs more E than melting as all forces must break. KE and hence temp contstant. Gas bubbles visible throughout liquid
Gas heated under pressure, KE and temp increase
Basic assumptions of kinetic theory as applied to a ideal gas:
Ideal gas strictly obeys these:
- Molecules are in continuous random motion
- Volume occupied by molecules negligible compared to total volume occupied by gas. Ie molecules are point masses
- Intermolecular force of attraction is negligible
- Colliding molecules, perfectly elastic, no loss/gain of E
- Pressie of gas is due to collision of molecules against containers walls
Temp in Kevin is known as
Absolute temp
Absolute zero, 0K, is…
Point of zero kinetic energy of particles
0K=
-273°C
Celsius –> Kelvin ?
Add 273
How many Pa in 1 bar
10^5 ie 1 atm
Cm3 –> dm3 ??
Divide by 1000
1000cm3=xdm3
1dm3
Dm3 –> m3 ??
Divide by 1000
1m3=xdm3
1000dm3
Boyle’s law:
Volume occupied by fixed mass of gas varies inversely with it’s pressure at constant temp
Volume of gas=
Containers volume
Pressure increases as
Frequency or energy of collisions increases
Boyle’s law relationship
P α 1/V
PV is a constant
Graphs of Boyle’s law
V X axis, p y axis. Decreasing curve
1/V X axis, P y axis. Straight line through origin
P X axis, pv y axis. Constant (—)
Charles law:
Volume of given mass of gas directly proportional to it’s absolute temp, at constant pressure.
Charles law relationship
VαT
V/T= a constant
Charles law graph
Temp/K X axis, V y axis. Straight line through origin which is absolute 0 (0K)
Relationship between temp and pressure
Increase in temp increase average KE of particles and they move faster and collide walls with more energy and frequency, raising pressure.
If volume is held constant pressure directly proportional to absolute temp
PαT
P/T= a constant
Graph of PαT
Temp/K X axis, P y axis. Straight line through 0K at origin
Charles laws:
VαT at const P
PαT at const V
Combined gas law equation
PV/T= a constant
OR
P1V1/T1=P2V2/T2 (1-ini, 2-fin)
Ideal gas equation:
PV=nRT
Derived from 3 gas laws for fixed mass of gas
Practice the derivation
Avogadros law:
V α n
At const temp, and pressure, equal volumes of gases contain equal no of moles
What is R?
Universal gas constant
When using ideal gas equation, P must be in: 1. V: 2. No of moles: 3. Temp: 4.
- Pa
- m3
- m/M
4: K
How do real gases behave
Deviated to some extent from ideal behavior
Ideal gas defined as
Obeys ideal gas law PV=nRT under all conditions.
One mole of gas relationship PV/RT=1.
So graph of PV/RT against P for 1 mole is a horizontal line of intercept 1
Real gas almost behaves like an ideal gas at
Low pressure
High temp
Real gas shows greatest deviation at
High pressure
Low temp
How to interpret when real gases behave most and least like ideal gases
Question validity of 2 assumptions from kinetic molecular theory
1) volume of gas particles negligible
2) no attractive forces between particles
Explain why real gases can behave as ideal gases at low pressure, and not high in terms of volume
At low, volume of particles is about 0.05% of total so it’s valid to call it negligible
At high, space between then is reduced so percentage volume of particles increases to 20% of total - not negligible.
As a result, volume of real gas at high pres is larger than predicted from ideal gas law
Explain why real gases can behave as ideal gases at low pressure, and not high in terms of force of attraction
At low pressure, particles are wide spread so forces between are negligible. But high pressure, particles are closer so attractive forces strengthen. Reduce effect of pressure of gas.
Low temp increase deviation because lower KE increases strength of forces.
Which conditions being invalid make a real gas deviate from an ideal gas
High pressure and low temp molecules are close and volume occupied by individual molecules can’t be ignored compared to total. And intermolecular force of attraction is large and can’t be ignored
Particles in liquid :
- have more KE than those in solid state
- not in fixed positions
- in constant motion, bouncing or colliding off eachother
- closely packed but less than solid
- attrsctive forces less than in solid
Melting:
Solid changes its state when heated. Change happens because particles gain KE and vibrate with greater amplitude.
Melting point:
Temp at which energy supplied is sufficient to over come binding force
Vaporization :
Liquid surface is flat, expect near walls of container. this is because particles at surface are attracted inwards and sideways by other particles.
Fastest moving surface particles escape into gas state.
Why does temp decrease with evaporation
Escape of fastest particles decreases average KE of liquid so temp of liquid decreases with evaporation.
What increases rate of evaporation
Higher the temp the faster rate of evaporation.
Evaporation takes place at what temp
All the time
Because particles escape from surface all the time
Evaporation in closed container
Escaped particles collect in space above surface and collide with eachother and walls
Vapor pressure is
Vapor formed by escaping particles from particles in closed container exert a pressure
Vapor pressure depends on:
Temp of liquid
Characteristics of liquid as force holding particles is different for each
Saturated vapor pressure
As more and more particles escape molecules in vapor become close together and some condense back by hitting liquid surface.
When 2 opposing changes are at same time an equilibrium is reached (with molecules going from liquid to vapor as same rate as vapor to liquid) between no of particles leaving and reentering liquid when vapor pressure remains constant at given temp.
Pressure exerted by vapor at equilibrium is sat vap pres
Boiling
Liquid in contact with air is heated, it’s vapor pressure increases until a temp is reached at which vapor pressure = atmospheric pressure.
Liquid boils when …
Bp relationship with vapor pressure
Saturated vapor pressure = atmospheric pressure
Bp increases as vapor pressure does
Saturated vapor pressure is a characteristic of liquid. Meaning?
Constant for given liquid at given temperature (+temp, +KE, able to overcome)
Why does vapor condense back
Molecules in vapor come close as more molecules escape. Eventually molecules with lower KE are not able to over come attractive force of neighbouring molecules
At equilibrium concentration of water molecules in vapor is
Constant
