Top-Rated Free Essay # 5.09 Module 5 Review

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5317 Words Grammar Plagiarism  Writing  Score 5.09 Module 5 Review 05.09 Module Five Review and DBA
Phase Change | Liquid | Liquid-Gas
Phase Change | Gas | −40–0 (°C) | 0 (°C) | 0–100 (°C) | 100 (°C) | 100–130 (°C) | | melting point | | boiling point | | * What does the second horizontal section of the heating curve represent? This flat section of the graph represents the substance’s boiling point. When the liquid begins to boil, the temperature remains constant as the heat energy provided by the flame is used to move the particles farther apart to change the liquid to a gas. * A cooling curve: shows the temperature change as a substance loses energy and cools down. Cooling curves have the same horizontal sections that you saw in heating curves, where the phase changes from a gas to a liquid or from a liquid to a solid. Gas | Gas-Liquid
Phase Change | Liquid | Liquid-Solid
Phase Change | Solid | 130–100 (°C) | 100 (°C) | 100–0 (°C) | 0 (°C) | 0–−40 (°C) | | condensation point | | freezing point | | * 05.03 Gas Laws * Robert Boyle (1627-1691), an Irish born scientist, made many contributions to science through his study of gases. In 1661, he published "The Sceptical Chymist." In it, he argued that Aristotle's view of matter being made of four elements, fire, earth, air and water was incorrect. He proposed that matter was made of particles called atoms which moved around. Physical Characteristics and Variable | Typical Units | Volume (V) | Liters (L) | Pressure (P) | Atmosphere (atm) | Temperature (T) | Kelvin (K) | Number of particles (n) | Moles (mol) | Ideal gas constant, R | * x atm / K mol | * The SI unit of pressure is the Pascal (Pa), which is defined as one newton per square meter(N/m2). However, chemists most often use units of atmospheres (atm) or millimeters of mercury (mm Hg) to measure pressure. Units of Pressure | 1 atmosphere (atm) | = 760 mm Hg | | = 760 torr | | = 101.3 kilopascals (kPa) | * 785 mm Hg = ? atm * 785 mm Hg × 1 atm / 760 mm Hg = 1.03 atm * Temperature Conversions * When you want to convert from Celsius to Kelvin * K= 273.15 + oC * When you want to convert Kelvin to Celsius * oC= K-273.15 * The Nature of Gases * Low Density * The density of a substance in the gas phase is about 1/1,000 the density of the same substance as a liquid because the gas particles spread out so much farther from each other than they do as a liquid. * Compressibility * When enough pressure is applied, gases can be compressed to a smaller volume because there is so much space between the particles. With enough pressure, a gas can sometimes be compressed to a volume thousands of times smaller than its initial volume. * Expansion * Gases spread out to fill the entire container in which they are enclosed because the gas particles are moving in all directions with negligible attractive forces between them. This means that a gas transferred from a 2-liter container to a 4-liter container will expand, or spread out, to fill the entire 4-liter container. * Diffusion * Because of their high kinetic energy and random motion, gas particles can spread out and mix with each other without being stirred. The scent of ammonia travels through a room as its gas particles mix with the particles of air. * Fluidity * Gas particles are able to easily glide, or flow, past each other because the attractive forces between them are negligible. The term fluid is sometimes used to describe both liquids and gases because of their ability to flow. * The Kinetic Molecular Theory of Gases * The kinetic molecular theory of gases provides a model of an ideal gas that helps us understand the properties and behaviors of gas particles. An ideal gas is an imaginary gas that behaves according to all of the assumptions of the kinetic molecular theoryThe particles of a gas are in constant random motion. * The particles of a gas are in constant random motion. * Gases consist of large numbers of tiny particles. * The collisions experienced by gas particles are elastic collisions. * There are no forces of attraction or repulsion experienced between gas particles. * The average kinetic energy of the particles of a gas is directly proportional to the temperature, in Kelvin, of the gas. * Gas Laws * The pressure and volume of a sample of gas have an inverse relationship; as one of these values increases, the other decreases (and vice versa). This relationship is represented by the gas law known as Boyle's law, which compares an initial pressure and volume to a final pressure and volume when temperature and number of moles are held constant. * Boyle's law: P1V1 = P2V2

* 105 g NaCl × = 1.80 mol NaCl

* Molarity (M) =

* Molarity (M) =

* Molarity (M) = 0.514 M NaCl * Percent by Mass * The percent by mass of a solution: is the mass of solute (in grams) dissolved in a total of 100 grams of solution, expressed as a percentage. Notice that the numerator of the ratio is the mass of the solute alone, while the denominator is the mass of the solute plus the mass of the solvent to give the total mass of the solution. * Percent by mass (%) = × 100%

* or

* Percent by mass (%) = × 100%

* Percent by mass (%) = × 100%

* Percent by mass of CaCl2 = × 100%

* This solution is 10.7 % CaCl2 by mass.

* 05.07 Molarity and Dilution

* Solution Stoichiometry

* Mg (s) + 2 HCl (aq) → MgCl2 (aq) + H2 (g)

* 2.5 M HCl: This can be used as a conversion factor between moles of HCl and liters of HCl solution (). * 32.0 g Mg: This is the given amount of magnesium, which will be used to start the stoichiometry problem. * We are asked to solve for the volume of HCl solution (in milliliters). * Stoichiometry Set Up: * 32.0 g Mg × × × × = 1,050 mL of the HCl * Dilution * They can then dilute the stock solution by adding water until they have the exact concentration they need. * A stock solution is 28.2 percent ammonia (NH3) by mass, and the solution has a density of 0.8990 grams per milliliter. What volume, in milliliters, of this stock solution is required to prepare 600 milliliters of a 0.500 molar ammonia solution? * Diluted Solution: 600.0 mL volume, 0.500 M concentration * Stock Solution: 28.2% by mass, 0.8990 g/mL density, solve for volume in mL * Solve for Moles of Solute needed: * 600.0 mL NH3 solution (diluted) × × = 0.300 mol NH3 * Solve for the Volume of Stock Solution that Contains 0.300 moles of the Solute: * 0.300 mol NH3 solute × × × = 20.2 mL NH3 stock solution * 05.08 Colligative Properties * A colligative property: is a property of a solvent that depends on the number of solute particles dissolved in it, but not on the identity or nature of those solute particles. * Vapor Pressure * Vapor pressure: is the pressure exerted by the vapor particles that evaporate from a liquid (or solid). Vapor pressure can only be measured accurately when the evaporation occurs in a closed container. * As you increase the temperature of a liquid or solid, its vapor pressure also increases. On the other hand, vapor pressure decreases as the temperature of the liquid or solid decreases. * Vapor pressure of a solution * When a solute that does not evaporate well, it dissolves in a liquid to form a solution; the vapor pressure above that solution will be lower than the vapor pressure of the pure solvent. Remember that liquid particles at the surface of a liquid can escape to the gas phase when they have enough energy to break free of the liquid's intermolecular forces. * If we add solute particles to that liquid, the amount of surface area available for the escaping solvent molecules is reduced because some of that area is occupied by solute particles that are not able to evaporate. * Boiling Point * The boiling point: of a liquid is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure of the surrounding air. Because the vapor pressure of a liquid is lowered by the addition of a dissolved solute, the solution will need to be heated to a higher temperature for its vapor pressure to equal the atmospheric pressure. This is why dissolving a solute in a solvent increases the boiling point. * Freezing Point * Every liquid has a freezing point, the temperature at which a liquid undergoes a phase change from liquid to solid. As the liquid particles slow down, the attraction between the particles causes them to form solid crystal structures that lock them in place in the solid phase. * Molality * Molality is the concentration of a solution expressed in moles of solute per kilogram of solvent. * molality (m) =

* What is the concentration, in molality, of a solution made by dissolving 0.500 moles of ammonia (NH3) in 1.8 kilograms of water? * molality (m) =

* molality (m) =

* molality (m) = 0.28 m

* Ionic Solutes and Electrolytes * When an ionic compound dissolves, the ionic bonds are broken and the positive and negative ions separate from each other as they are surrounded by solvent particles. * Ionic solutes are categorized as electrolytes, solutes that dissolve in water to form solutions that are able to conduct an electrical current. Pure water does not conduct electricity well; it is the ions present in tap water and lake water that make it able to conduct electricity. Because ionic solutes break apart into individual ions when they dissolve, the number of total moles of solute is determined by the total moles of ions and not the moles of ionic formula units. * Change in Boiling Point * The boiling-point elevation of a solution is directly related to the concentration of the solution measured in the unit molality (m). This means that the more solute dissolved in a solution, the higher the resulting boiling point of that solution. * Δtb = Kbm * The triangle in this equation is the Greek letter delta, which is used by chemists to represent change, while the letter t represents temperature. Together, Δtb represents the boiling point elevation, or the increase in the boiling point of a solvent caused by the given amount of solute. The unit for the boiling-point elevation is degrees Celsius (°C). This change can be added to the normal boiling point of the pure solvent to determine the new boiling point of the solution. * This equation uses a constant, Kb, known as the molal boiling point constant. This constant is dependent on the identity of the solvent, but its unit is always expressed in degrees Celsius over molality (°C/m). * Change in Freezing Point * Δtf = Kfm * Δtf represents the freezing point depression, or the decrease in the freezing point of a solvent caused by the given amount of solute. The unit for the freezing-point depression is degrees Celsius (°C). The value of this change in temperature will always be negative because the freezing point of a solution is always lower than the freezing point of the pure solvent. * The molal freezing point constant of water is -1.86 °C/m * Determining the Molar Mass of a Solute * The solution is cooled or heated to observe the freezing-point depression or boiling-point elevation. This data can then be used to determine the molar mass of the solute. * Δtb/f = Kb/f

* molar mass of solute (g/mol) =

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