#9
In a solid particles are held together by strong intermolecular forces. The particles
are vibrating in place.
In a liquid particles are held together by intermolecular forces, but the forces are
weaker than in solids. These particles are vibrating and moving around somewhat.
In a gas particles are moving randomly all over the place because there are no
intermolecular forces. There is a lot of space between the particles and they are
moving quickly.
Absolute zero is 0 K and is the temperature at which all movement stops
Water usually boils at 100 oC, but if air pressure above the water is increased you
can make it boil at a temperature of 110 oC. Conversely, if you decrease the air
pressure above the water, you can get it to boil at a temperature less than 100 oC.
Another way to change the phase of a substance, like melting ice into water, is by
adding in heat. A reaction that absorbs heat to happen is an endothermic reaction.
To increase the pressure of substance you could add more gas particles, decrease
the volume or increase the temperature
A graph of a direct relationship would slope uphill. A graph of an indirect relationship
would slope downhill
Pressure and temperature are directly related, volume and temperature are directly
related, but pressure and volume are indirectly related. If pressure increases, then
temperature increases but volume decreases.
760 torr, 1 atm, and 101.3 KPa are standard (STP) measurements for pressure and 0
o
C and 273K are standard measurements for temperature.
30 °C = 303 K
°C
18. 650 K = 27 °C
19. 100 °C = 373 K
20. 100 K = -173
Answer Bank
0 oC
1 atm
101.3 KPa
-173
273 K
3.44
303
373
377
760 Torr/mmHg
Absolute zero
Decreases
Dense
Downhill
Endothermic
Heat
Increased
Less
More
No
Pressure
Quickly
Randomly
Solid
Stops
Temperature
Uphill
Volume
Volume
Volume
Water
Weaker
A 3 L sample of Ne is at 50C. What volume does the same sample of Ne occupy at 98C? 3.44L
Most solids are more dense than their liquid forms. Water is the exception
How many moles of N2 gas are there in 0.750L container that is at 200K and at 3.25 atm? 0.015 moles
Which letter represents the rising temperature
during the liquid phase? C
E
Which letter shows the phase change from a solid
to a liquid? B
D
C
Which letter shows freezing? B
B
What is the boiling point of this substance? 100
A
Moving from A on the graph to E is an endothermic
reaction.
Moving from E to A on the graph is an exothermic reaction.
Solid  liquid = melting
Solid  gas = sublimation
Liquid  solid = freezing
Liquid  gas = boiling/vaporization
Gas  liquid = condensation
As temperature increases the rate of motion (kinetic energy) of the particles in a
substance increases
Phase changes do not change the chemical composition of a substance and that is
why they are reversible
Units of volume = L and mL
Units of pressure = atm, KPa, mmHg, and Torr
Units of temperature = K and oC
Which letter shows the solid phase? A
Which letter shows the liquid phase? E
Which letter shows the gas phase? B
Answer Bank
Chemical
Condensation
Endothermic
Exothermic
Freezing
Increases
Melting
Pressure
Pressure
Reversible
Sublimation
Temperature
Vaporization
Volume
Which letter show the triple point? D
E
The triple point shows the temperature and pressure where all 3 phases
of matter can occur all at the same time.
A
1atm
C
P
D
Temp
B
Increases
q = m C T How many joules of heat are released when 5 g of a
substance is cooled from 30 oC to 20 oC? The specific heat of the
substance = 2.06 J/g oC -103joules
As a reward for those of you who decided to take the time to review your answers – Send me an
email with the triple point numbers for water – need temperature and pressure (google – what is the
triple point of water? To get answer). Be sure to include your name in your email since email
addresses can be cryptic. This will get you 4 points added to homework but deadline is Monday
3/25/13.