Embed Size (px)
Citation preview
10.4CHANGES OF STATE
10.4 NOTES
The state of matter depends on temperature and pressure.
(Pressure mostly affects gases.)
10.4 NOTES
The state of matter depends on temperature and pressure.
(Pressure mostly affects gases.)
When energy (usually heat) is added, the kinetic energy of the particles increases, and the particles can gain enough energy to overcome the attractive forces holding them together.
10.4 NOTES
The state of matter of a particular substance depends on temperature and pressure. (Pressure mostly affects gases.)
When energy (usually heat) is added, the kinetic energy of the particles increases, and the particles can overcome the atractive forces holding them together.
solid liquid gas
melting vaporizing
10.4 NOTES
The state of matter of a particular substance depends on temperature and pressure. (Pressure mostly affects gases.)
When energy (usually heat) is added, the kinetic energy of the particles increases, and the particles can overcome the attractive forces holding them together.
solid liquid gas
melting vaporizing
When particles slow down, they lose kinetic energy, and intermolecular forces start binding one particle to another.
solid liquid gas
freezing condensing
10.4 NOTES
The state of matter of a particular substance depends on temperature and pressure. (Pressure mostly affects gases.)
There are a few substances which skip the liquid phase.
solid gas gas solid
subliming depositing
10.4 NOTES
The state of matter depends on temperature and pressure.
(Pressure mostly affects gases.)
When pressure increases, distances between particles decreases, and attractive forces are able to attract particles easier.
10.4 NOTES
How does boiling compare to evaporation?
10.4 NOTES
Boiling involves the gas inside the liquid overcoming the pressure above the liquid, usually energy has been added
to transform the liquid particles into
gas particles.
10.4 NOTES
Boiling involves the gas inside the liquid overcoming the pressure above the liquid, usually energy has been added
to transform the liquid particles into
gas particles.
The pressure above the liquid is usually
the atmospheric pressure, so the liquid
will not boil until the pressure inside
the gas bubbles equals the atmospheric
pressure.
P. 344 shows various liquids and how their
boiling points vary.
10.4 NOTES So what is atmospheric pressure? Where does it come from? Why don’t we feel it?
10.4 NOTES
Evaporation involves liquid particles at the surface having enough kinetic energy to overcome intermolecular forces, and escape the liquid.
10.4 NOTESPhase diagrams show the relationship between the three
common phases of matter and the temperature and pressure that control them.
10.4 NOTESLines show phase changes.
The triple point is the temperature and pressure where all three phases exist simultaneously.
Critical point is the point at which the substance is neither a liquid nor a gas. It is called a supercritical fluid.
1. At what pressure and temperature do all 3 phases exist simultaneously?
2. If I have a bottle of compound X at a pressure of 45 atm and a temperature of 100 *C, what will happen if I raise the temperature to 400*C (keeping pressure constant?3. Why can’t compound X be boiled at 200*C?
4. If I wanted to could I drink compound X?
5. If I have a bottle of compound X at a pressure of 25atm and a temperature of 500*C, and the pressure is raised while keeping the temperature constant, what phase change(s) would it go through?
10.4 NOTES
Heating and cooling curves show changes in a substance as heat is either applied or removed.
(Assume even heating)
10.4 NOTES
What is the molar heat of fusion?
10.4 NOTES
The molar heat of fusion (ΔHf) is the energy required to completely melt one mole of a substance. The same amount of energy is released as one mole of the substance freezes.
Solid + energy liquid or liquid solid + energy
The molar heat of vaporization (ΔHv) is the energy required to completely vaporize one mole of a substance. The same amount of energy is released as one mole of the substance condenses.
liquid + energy vapor or vapor liquid + energy
10.4 NOTES
Why during melting does the temperature remain constant even though heat is being added?
Where is the energy going?
Using the graph how would you calculate the heat of fusion? Heat of vaporization?
10.4 NOTES
The kinetic energy being added is changing into potential energy as the particles move further apart. The speed of the particles (kinetic energy) doesn’t change because the temperature doesn’t change, but they are breaking the attractive forces and moving further apart.
10.4 NOTES
Why would the heat of vaporization be so much higher than the heat of fusion?
10.4 NOTES
EXAMPLE PROBLEMS:
1. The chlorofluorocarbon, CCl3 F, has a heat of vaporization (∆Hv) of 24.8 kJ/mol. To vaporize 1.00 kg of the compound, how much heat is required?
10.4 NOTES
EXAMPLE PROBLEMS:
2. It requires an addition of 6.100 kJ of energy to melt 41.65 g of NaI. What is its molar heat of fusion (∆Hf)?
10.4 NOTES
EXAMPLE PROBLEMS:
3. Some camping stoves contain liquid butane, C4 H10 . Assume the heat of vaporization is 24.3 kJ/mol. If the camp stove contains 190g of liquid butane, how much heat is required to vaporize all of the butane? (∆Hv = 24.3 kJ/mol)
10.4 NOTES
EXAMPLE PROBLEMS:
4. The molar heat of vaporization of methanol is 38.0 kJ/mol at 25ºC. How much heat is required to convert 250 mL of the alcohol from liquid to vapor? (The density of methanol, CH3OH, at this temperature is 0.787 g/mL.)
