States of Matter. Mr. Solsman Chapter 12. What makes solids, liquids, and gases different?. What are the macroscopic differences? What are the molecular level interactions that cause these differences? What are the molecular level changes that must happen for phase change to happen?
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1. All gases are composed of tiny particles called molecules.
2. These molecules are in constant random motion.
3. On an average, these molecules are far apart.
4. If the temperature cools, molecular velocities decrease. Inother words, the average kinetic energy goes down.
5.Molecules are perfectly elastic. They experience no net loss of energy on collision.
6.There are attractive forces between the molecules of a gas.
Gases easily flow past each other because there are no significant forces of attraction.
Graham’s law of effusion states that the rate of effusion for a gas is inversely proportional to the square root of its molar mass.
Ammonia has a molar mass of 17.0 g/mol; hydrogen chloride a molar mass of 36.5 g/mol. What is the ratio of their diffusion rates?
The particles in the earth’s atmosphere exert pressure in all directions called air pressure.
Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases of the mixture.
Pt = P1 + P2 + P3 + ……+ Pn
A mixture of oxygen, carbon dioxide, and nitrogen has a total pressure of 0.97 atm. What is the partial pressure of oxygen if the partial pressure of carbon dioxide is 0.70 atm and the partial pressure of nitrogen is 0.12 atm?
Suppose 10.1 g of Ne, 8.00g O2 , and 2.80 g N2 are mixed in a flask. If the total pressure is .500 atm, what is the partial pressure of each gas?
If 16.0 grams of oxygen, 2.0 grams of hydrogen, 8.00 grams methane, and 8.0 grams of He are mixed for a total pressure of 4.00 atm, what are their individual partial pressures?
All liquids are composed of clusters of particles weakly bonded* to each other but free enough to move over one another**.
* This explains the definite volume.
**This explains no definite shape.
CH4 16.0 -161 0C
H2O 18.0 +100.0 0C
CO2 44.0 -56.6 0C
As attractive forces become greater, the amount of energy needed to overcome the force is greater and the boiling temperature is higher.
All solids are composed of one giant cluster or aggregate of particles strongly bonded to each other in fixed positions*, but free enough to vibrate and rotate about those positions.
* This accounts for the definite volume and shape of a solid.
A.The molar volume of N2(g) at STP is 22.4 liters/mole.
B.The molar volume of N2(s) at -2100C is 27.2ml/mole.
Phase Changes are physical changes. There is no loss in identity. The molecular, atomic, or empirical formulas do not change.
Na+Cl-(s) Na+Cl-(l) - MELTING
H2O(l) H2O(g) -EVAPORATION
CO2(s) CO2(g) -SUBLIMATION
Ne(g) Ne(l) - CONDENSATION
H2O(g) H2O(s) -DEPOSITION
Cu(l) Cu(s) -FREEZING
MOLAR HEAT OF VAPORIZATION – the amount of heat needed to vaporize one mole of a liquid at its boiling point.
MOLAR HEAT OF MELTING(FUSION) – the amount of heat needed to melt one mole of a solid at its melting point.
1. Melting 1.44 kcal + H2O(s) H2O(l)
2. Evaporation 4.88 kcal + Cl2(l) Cl2(g)
3. Sublimation 18.1 kcal + CO2(s) CO2(g)
In each of these: Low PE High PE
As energy is absorbed from the surroundings at constant temperature, bonds break and potential energy rises. These produce a cooling effect.
Freezing H2O(l) H2O(s) + 1.44kcal
Condensation Ne(g) Ne(l) + 0.405kcal
Deposition H2O(g) H2O(s) +11.3kcal
In each of these: High PE Low PE
Potential energy drops as bonds form at constant temperature. Energy is released to the surroundings. These produce warming effects.
Substance Heat of Fusion Heat of Vap
Ne 0.080kcal 0.405kcal
H2O 1.44kcal 9.7kcal
NaCl 6.8kcal 40.8kcal
Cu 3.11kcal 72.8kcal
Why is the heat of vaporization so much greater than the heat of fusion?
How much heat does it take to completely vaporize 100. grams of room temperature(25 ºC) water?
= 31,400 J + 224,000 J = 255,000 J