To compare one gas to another, it is convenient to define a set of conditions: Standard Temperature and Pressure

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1 Standard Molar Volume To compare one gas to another, it is convenient to define a set of conditions: Standard Temperature and Pressure At STP, one mole of any gas has a volume of: 22.4 L = (This is a cube about 28cm or 11 in on each side.) Problem: a) How many moles of methane gas, CH4, are in a 1.00 x 10 5 L storage tank at STP? b) How many grams of methane is this? c) How many grams of CO2 could the same tank hold? 8.8 The Combined Gas Law The previous relationships can all be combined into a single equation. This relationship is true under any set of conditions. T must be in K V & P can be in any units. This is typically used when you are changing conditions for a given sample of a gas. This formula can be used to solve any of the previous gas laws. If a variable is constant, simply eliminate it! Ch 08 Page 17

2 Problem: A sample of CO 2 gas in flask A (V= 265 ml & P= mm Hg, at T= 22.5 C). The sample is moved to another flask (B), with (P= 94.3 mm Hg & T=24.5 C). What is the volume of flask B? 8.10 The Ideal Gas Law Derivation: P 1 V 1 = P 2 V 2 = a constant at all sets of conditions n 1 T 1 n 2 T 2 Since the relationship is always true, it is always equal to a constant, R. R = Whenever we use R, V must be in P must be in T must be in The relationships among the four variables P, V, T, and n can be rearranged into a single expression. Ideal Gas Law Ch 08 Page 18

3 Problem: A sample of H 2 gas has a volume of 5.86 L at 0 C. It exerts a pressure of 1140 torr. How many moles of H 2 are in this sample? 8.11 Dalton s Law of Partial Pressures States that: The pressure of a mixture of gases = the sum of the pressure exerted by each individual component = the sum of the partial pressures. The pressure contributed by each gas is independent of any other gas present. Each gas contributes to the pressure as if it was the only gas present in the entire volume. Air is a mixture of about 21% oxygen, 78% nitrogen, and 1% argon. This means that 21% of atmospheric pressure is caused by the oxygen, 78% by nitrogen, and 1% by argon. Pi = (Ptotal) (% i) Note: % I must be expressed as a decimal.) If the total air pressure is 780 mm Hg, the partial pressures of each gas are: oxygen 780 mm Hg nitrogen 780 mm Hg argon 780 mm Hg The partial pressures should always add up to the total pressure and the percentages should always add up to 100%! Ch 08 Page 19

4 Problem: Assuming a total pressure of 9.5 atm, what is the partial pressure of each component a the mixture of 98% helium and 2.0% oxygen breathed by deep sea divers? Problem: Determine the percent composition of air in the lungs from the following composition in partial pressures: Pnitrogen = 573 mm Hg, Poxygen = 100 mm Hg, Pcarbon dioxide = 40 mm Hg, Pwater = 47 mm Hg. They should add up to 100 (+/- 0.1 for rounding errors.) Problem: What is the partial pressure of oxygen in the air at an altitude where the atmospheric pressure is 685 mm Hg? (Air contains 21% oxygen) (Ans:144 mmhg) Ch 08 Page 20

5 8.12 Liquids Properties of Liquids Chapter 8 Part 2 - Liquids, and Solids Vapor Pressure Molecules are in constant motion in the liquid state. If a molecule has enough energy, it can break free of the liquid and escape into the gas state, called. If a liquid is in a closed container, the random motion of the molecules occasionally brings them back into the liquid. Evaporation and condensation take place at the same rate, and the concentration of vapor in the container is constant. is the partial pressure of vapor molecules in equilibrium with a liquid. - Vapor pressure depends on both and of a liquid. Liquids with a high vapor pressure evaporate than those with a low vapor pressure. The contribution to the total pressure in the container from the vapor molecules (it s partial pressure) is referred to as its vapor pressure. Ch 08 Page 21

6 Effect of Temperature and Pressure The the temperature, the the vapor pressure. When the vapor pressure reaches, the liquid will. If the ambient pressure is, the liquid will boil at a temperature. The boiling point when the pressure is 1 atm is the Viscosity Viscosity is the measure of a liquid's. 1. SI unit - N.s/m2. 2. Ease with which molecules move around in the liquid. 3. Related to intermolecular forces. - the forces the greater the the viscosity. Substances such as gasoline (small nonpolar molecules) have low viscosities. Substances such as glycerin (larger more polar molecules) have higher viscosities.. Ch 08 Page 22

7 Viscosity is the property that is used to rate (SAE 10W40) SAE stands for the Society of Automotive Engineers Oils meeting the SAE's low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). An oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by the length of time it takes to flow out of the hole. If it flows quickly, it gets a viscosity rating. If it flows slowly, it gets a viscosity rating. Surface Tension The resistance of a liquid to and increasing its surface area. 1. Due to the difference in intermolecular forces felt by the molecules on the surface of the liquid and the molecules in the interior of the liquid. 2. Related to intermolecular forces. a. the forces the the surface tension Ch 08 Page 23

8 Water: A Unique Liquid Interesting Facts Water covers over 70% of the earth s surface. The human body is made up pf 66% water. Water has the highest specific heat of any liquid. - It takes a great deal of heat to change the temperature of water. - This makes it easier for our bodies to maintain a steady internal body temperature. - This is why climates are more temperate near large bodies of water. Water also has an unusually high heat of vaporization. This means that it carries away large amounts of heat when it evaporates. This is how sweating keeps us cool. This is why we get into so much trouble during heat stroke (we stop sweating. Water is one of the only substances that become less dense when it freezes. This causes ice to float rather than sink. This keeps our lakes and oceans from freezing solid. As water freezes, each molecule is locked into position by hydrogen bonding to 4 other molecules. The resulting structure has more open space than liquid water, accounting for it s lower density. Ch 08 Page 24

9 8.13 Solids Kinds of Solids Crystalline solids Solids whose atoms, molecules, or ions are rigidly held in an ordered arrangement. - Ionic solids Particles are. (example: NaCl). Ordered into a 3-D arrangement of alternating + and ions and is held together by - Molecular solids Particles are held together by. (example: sucrose (sugar) or solid dry ice) - Covalent network solids Particles are linked by into a 3-D array. (eg: diamond or quartz) - Metallic solids They can be viewed as vast three-dimensional arrays of metal cations immersed in a sea of electrons. o The electron sea acts as a glue to hold the cations together and as a mobile carrier of charge to conduct electricity. o Bonding attractions extend uniformly in all directions, so metals are malleable rather than brittle. When a metal crystal receives a sharp blow, the electron sea adjusts to the new distribution of cations. Ch 08 Page 25

10 Amorphous solids Particles are arranged and have no ordered long-range structure. (example: glass, tar, and polymers) Amorphous solids o soften over a wide temperature range and o shatter to give pieces with curved rather than planar faces Ch 08 Page 26

11 8.14 Changes of State Calculations When heat is added to a solid, it goes through various changes. The changes can be shown on a heating curve. Heat of Fusion: The quantity of heat required to completely melt one gram of a substance once it reaches its melting point. Heat of Vaporization: The quantity of heat required to completely vaporize one gram of a substance once it reaches its boiling point. Formula for determining heat required for melting: Formula for determining heat required for vaporizing: Formula for determining heat required to change the temperature of a substance while keeping the phase constant: Ch 08 Page 27

12 For all phase change calculations: Mass in grams T in K or C c in cal/ g C or in J/g C heat in cal/g or in J/g Problem: How much heat (in kcal) is required to take 1.50 mol of solid isopropyl alcohol (rubbing alcohol, mm=60.0 g/mol) at its melting point of C, melt it, raise the liquid to the boiling point of 82.0 C, and vaporize all it? (The heat of fusion is 21.4 cal/g, the heat of vaporization is 159 cal/g, and the specific heat of the liquid is cal/g C.) Ch 08 Page 28