CHANGES OF STATE Design: Metro Color: Office 10.4

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.

How does boiling compare to evaporation? 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.

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.

So what is atmospheric pressure? Where does it come from? 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.

Phase diagrams show the relationship between the three common phases of matter and the temperature and pressure that control them. 10.4 NOTES

Lines show phase changes Lines 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. 10.4 NOTES

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: 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.)