Phases
Phases Thursday, July 25, 2013
2:42 PM
1. Solids have a definite shape and a definite volume a. The molecules do not change positions, resulting in a fixed structure, whose molecules are in contact with neighboring molecules at all times 2. Liquids have a definite volume but no definite shape a. The molecules change position (translational motion) resulting in continuous random motion, and molecules that remain in contact with neighboring molecules at all times 3. Properties of solids a. The molecules of a solid are arranged in a fixed lattice structure, on the macroscopic level, they have repeating structure subunits called unit cells b. Thus, the structure of a crystalline solid is defined by the size and shape of the unit cell and the locations of atoms within the unit cell c. The three most common unit cells are the simple cubic with one atom per repeating unit cell, the body-centered cubic with two atoms per repeating unit cell, and the face centered cubic, with four atoms per repeating unit cell
i.
General Chemistry Page 1
ii.
d. Alkaline metals often pack to form the simple cubic e. Gold and silver pack to form a face-centered cubic f. Solids have density 4. Properties of liquids a. No definite shape, but they do have a definite volume b. Because their molecules are in motion, liquids can flow, which defines them as a fluid c. Liquids typically have the highest heat capacity of the three common phases, and liquids are compressible d. The density of a liquid decreases with increasing temperature (because the volume increases but the mass remains the same), with the EXCEPTION OF WATER FROM 0C to 4C e. IF A COMPOUND IS LIQUID AT ROOM TEMPERATURE, IT HAS A MELTING POINT LESS THAN ROOM TEMPERATUER AND A BOILING POINT GREATER THAN ROOM TEMPERATURE f. Surface tension generally increases as the intermolecular forces increase i. It is defined as the energy required to increase the surface area of a liquid by a unit amount 5. Phase Change Processes a. A phase change process is a physical process, not a chemical process, by which the state of matter changes b. In a phase change, the molecules themselves do not change, but the interactions between molecules do
c.
d. e. f. g. h.
Isothermal - Conditions where the temperature of the system does not change Isobaric - pressure is constant Isochoric - volume does not change Adiabatic - system is perfectly insulated, so that heat neither enters nor exits the system (qconstant) 6. Phase Diagrams a. A phase diagram summarizes the different states of matter for a given compound or General Chemistry Page 2
a. A phase diagram summarizes the different states of matter for a given compound or element with respect to temp and pressure b. Water has an atypical phase diagram i. The difference is the negative slope associated with the line separating liquid from solid ii. Most compounds can be compressed from a liquid into a solid at constant temperature iii. The unusual thing about water is that an isothermal increase in pressure compresses the solid (ice) into liquid water, resulting in the liquid being denser than the solid 7. Water facts a. Its liquid from is denser than its solid form b. Its densest at 4 degrees Celsius c. The solid can be compressed into a liquid under relatively mild conditions d. Water has the densest hydrogen bonding of any compound 8. Supercritical fluids a. A supercritical fluid exists when the conditions exceed the critical point b. A gas normally liquefies at some point when pressure is applied i. A cylinder containing water vapor at 100 degrees celcious will form liquid water if 760 torr of pressure is applied ii. If the temperature is 110 degrees, the liquid phase does not form unti the pressure is 1075 iii. At 374 degrees, the liquid phase only forms at 1.655e5 torr iv. Aboce this temperature, no amount of pressure causes a distinct liquid phase to form v. Instead, as pressure increases, the gas becomes steadily more comperssed c. The highest temperature at which a distinct liquid phase can form is called the critical temperature d. The critical pressure is the pressure required to bring about liquefaction at this critical temp e. When the temp exceeds the crit temp, and the pressure exceeds the crit pressure, the liquid and gas phase are indistinguishable from each other, and the substance is in a state called a supercritical fluid 9. Heating Curve
a.
b. A material is heated or cooled at a constant rate under isobaric conditions over a broad temperature range c. Shows the SAME features as a horizontal line in a standard phase diagram, but in significantly more detail d. If we heat an ice cube initially at -25C at 1 atm, the temperature of the ice increases e. As long as the temp is below 0, the ice cube remains in the solid state f. When the temp reaches 0, the ice begins to melt g. Because melting is an endothermic process, the head we add at 0C is used to convert ice to liquid water, and the temperature remains constant until all the ice has melted General Chemistry Page 3
liquid water, and the temperature remains constant until all the ice has melted i. The enthalpy of vaporization is greater in magnitude than the enthalpy of fusion (length of the blue lines) because more energy is necessary to break the intermolecular forces (going from a liquid to gas) than is necessary to weak the intermolecular forces (solid to liquid) h. We can calculate the enthalpy change of the system for each segment of the heating curve i. The amount of heat needed to raise the temperature of segment AB, CD, and EF is calculated by the product of the specific heat, mass and temperature change ii. The greater the specific heat of a substance, the more heat we must add to accomplish a certain temp change iii. The slope of the line is inversely proportional to the heat capacity 1) The flatter the line, the greater the heat capacity i. The slope for each of the three phases are different, implying that the heat capacities for each of the three phases are different j. The heat capacity of the liquid Is the greatest of the three phases 10. Vapor Pressure a. About every liquid and solid (more so liquid) there is a finite amount of vapor formed when molecules at the surface layer escape b. A vapor is composed of gas particles that are in in equilibrium with the liquid phase, so they temporarily exist as gas, until they condense back into their more favorable phase c. "Force per unit area above the surface of a liquid exerted by molecules formed upon evaporation of the liquid" i. The vapor pressure of a liquid is simply the partial pressure exerted by the gas molecules formed by evaporation when it is in equilibrium with the gas molecules condensing back into the liquid d. The vapor pressure above a pure liquid depends on the temperature of the liquid and the Δhvaporization of the liquid
e.
f. It is difficult to measure the vapor pressure of an open system so we generally consider vapor pressure in an open system from a theoretical perspective, and apply values that have been determined previously in a closed system at known temperatures g. VAPOR PRESSURE IS INDEPENDENT OF THE SHAPE AND VOLUME OF THE CAINTINER i. The same amount of the liquid is vaporizing from each system per unit area of its surface, as long as the temperature of both systems is the same
1)
ii. The rate of vaporization is greater with the greater surface area, but the vapor General Chemistry Page 4
ii. The rate of vaporization is greater with the greater surface area, but the vapor pressure is still the same h. Vapor pressure increases as temperature increases but decreases as Δhvaporization increases i. As boiling point increases, the ability for a compound to vaporize decreases i. This means as the boiling point increases, less of the vapor is formed and consequently the vapor pressure decreases 11. Vapor Pressure Graphs a. Vapor pressure increases as the temperature of the solution increases, but NOT IN A LINEAR FASHION
i.
b. The graph CANNOT intersect the y-axis when the units of temp are kevelin and axis originates at zero c. For each substance, the vapor pressure curves sharply upward with increasing temperatur d. Relationship is given by the Clausis-Clapeyron equation i.
ii. e. The equation predicts that a graph of ln P versus 1/T should give a straight line with a slope equal to Δhvap/R 12. Boiling point a. The boiling point is the temperature above which a substance may not exist as a liquid OR the temperature at which the vapor pressure of a liquid is equal to the atmospheric pressure b. At reduced atmospheric pressure the boiling point of a liquid is lower than normal c. Under cases of increased pressure, the boiling point is higher than normal d. The greater the molecular mass of a compound, the harder it is to vaporize it, which means the greater the boiling point 13. Boiling point variations a. The boiling point of a compound can be altered either by varying the atmospheric pressure or by varying the intermolecular forces b. Boiling point increases as soluble impurities (such as salt) are added to solution i. The liquid has a greater tendency to stay a liquid 14. Rauolt's Law a. The vapor pressure above a solution of two or more miscible liquids depends on the mole fraction of each compound in solution b. A solution consisting of a volatile liquid solvent and a nonvolatile solute forms spontaneously because of the increase in entropy that accompanies their mixing c. If effect, the solvent molecules are stabilized in their liquid state by this process and this have a lower tendency to escape into the vapor state d. Therefore, when a nonvolatile solute is present, the vapor pressure of the solvent is lower than the vapor pressure of the pure solvent
General Chemistry Page 5
i.
e. The vapor pressure of a volatile solvent above a solution containing a nonvolatile solute is proportional to the solvents concentration in the solution i. ii. X = mole fraction of solvent iii. Po=vapor pressure of pure solvent f. Because molecules interact in both the liquid and gas phases, the vapor pressure relationship is not as linear as Raoult's equation i. If there is an overall increase in attractive forces in solution when the components are mixed, then vaporization, and thus vapor pressure, decreases ii. If there is an overall decrease in attractive forces in solution when the components are mixed, then vaporization, and thus vapor pressure increases 15. Distillation a. Used to remove a liquid from a solution b. To do so, the liquid must first be converted into vapor, and then the vapor is allowed to flow up a distilling column 16. Colligative properties a. Properties of a solution that are affected by the concentration of a soluble impurity, but not the KIND OR IDENTIY OF THE SOLUBLE IMPURITY b. As impurities are added to a solution, the solvent has a greater tendency to remain as a liquid c. When freezing saltwater, the freezing point of the salt solution continues to decrease as water freezes away from the solution because the molality of the impurity in the solution is increasing as water is removed. Same with boiling
i.
17. Boiling point elevation a. The increase in boiling point (and thus decrease in vapor pressure) is attributed to decreased surface area from which the liquid can evaporate and an increase in the intermolecular forces binding the liquid in solution General Chemistry Page 6
intermolecular forces binding the liquid in solution b. In the case of saltwater solution, water has stronger attraction to the ionic impurities than it does to other water molecules
i.
c. i. Kb is the constant for the solvent ii. I is the van't hoff factor (ionizavility constant--essentially the number of ions that form upon dissolving) iii. m is the molality d. Freezing point depression i. 18. WHEN SUGAR DISSOLBES IN WATER< THE I VALUE IS 1 a. IT DOES NOT FORM ANY IONS. REMAINS INTACT 19. Osmotic Pressure a. Water has a natural tendency to flow from solutions of higher water concentration to lower water concentration to reach equal concentrations b. Pressure causes water to flow, called osmotic pressure i. Force per unit area exerted by a solution throug osmosis across a smepiermeable memb rane ii. c. U-tubes are separated by a semi=oermeable membrane and allow nautral polymers like proteins to be separated by mass i. Only water can pass through the membranes ii. Water will continue to flow untill osmotic pressure equals the hydrostatic pressure, density*g*Δh
iii.
d. Once the water levels reach a fixed height, molarity can be determined, which can be converted to moles e. A given mass of protein was used, so the molecular mass is found by dividing the number of moles 20. Conductance a. Pure water does not conduct electrical current because there are no ions present in the solution General Chemistry Page 7
solution b. The specific conductance of an aqueous salt solution is directly proportional to the concentration of salt in solution c. Condosity is the molar concentration of an aqueous sodium chloride solution that has the same specific conductance as the aqueous salt solution d. Salts that form aqueous solutions capable of conducting electricity better than sodium chlroide solutions have a condosity greater than their molarity e. The greater the ratio of condosity to molarity, the better the salt at conducting electricity If I have a 2 M solution of KCl, what would we expect the condosity to be? Condosity is the concentration (Molarity) of an NaCl solution that will conduct electricity exactly as well as the solution in question. Since K is more metallic than Na, we know that it is a better conductor. Therefore, the condosity will be something greater than 2. From
General Chemistry Page 8
2:42 PM
1. Solids have a definite shape and a definite volume a. The molecules do not change positions, resulting in a fixed structure, whose molecules are in contact with neighboring molecules at all times 2. Liquids have a definite volume but no definite shape a. The molecules change position (translational motion) resulting in continuous random motion, and molecules that remain in contact with neighboring molecules at all times 3. Properties of solids a. The molecules of a solid are arranged in a fixed lattice structure, on the macroscopic level, they have repeating structure subunits called unit cells b. Thus, the structure of a crystalline solid is defined by the size and shape of the unit cell and the locations of atoms within the unit cell c. The three most common unit cells are the simple cubic with one atom per repeating unit cell, the body-centered cubic with two atoms per repeating unit cell, and the face centered cubic, with four atoms per repeating unit cell
i.
General Chemistry Page 1
ii.
d. Alkaline metals often pack to form the simple cubic e. Gold and silver pack to form a face-centered cubic f. Solids have density 4. Properties of liquids a. No definite shape, but they do have a definite volume b. Because their molecules are in motion, liquids can flow, which defines them as a fluid c. Liquids typically have the highest heat capacity of the three common phases, and liquids are compressible d. The density of a liquid decreases with increasing temperature (because the volume increases but the mass remains the same), with the EXCEPTION OF WATER FROM 0C to 4C e. IF A COMPOUND IS LIQUID AT ROOM TEMPERATURE, IT HAS A MELTING POINT LESS THAN ROOM TEMPERATUER AND A BOILING POINT GREATER THAN ROOM TEMPERATURE f. Surface tension generally increases as the intermolecular forces increase i. It is defined as the energy required to increase the surface area of a liquid by a unit amount 5. Phase Change Processes a. A phase change process is a physical process, not a chemical process, by which the state of matter changes b. In a phase change, the molecules themselves do not change, but the interactions between molecules do
c.
d. e. f. g. h.
Isothermal - Conditions where the temperature of the system does not change Isobaric - pressure is constant Isochoric - volume does not change Adiabatic - system is perfectly insulated, so that heat neither enters nor exits the system (qconstant) 6. Phase Diagrams a. A phase diagram summarizes the different states of matter for a given compound or General Chemistry Page 2
a. A phase diagram summarizes the different states of matter for a given compound or element with respect to temp and pressure b. Water has an atypical phase diagram i. The difference is the negative slope associated with the line separating liquid from solid ii. Most compounds can be compressed from a liquid into a solid at constant temperature iii. The unusual thing about water is that an isothermal increase in pressure compresses the solid (ice) into liquid water, resulting in the liquid being denser than the solid 7. Water facts a. Its liquid from is denser than its solid form b. Its densest at 4 degrees Celsius c. The solid can be compressed into a liquid under relatively mild conditions d. Water has the densest hydrogen bonding of any compound 8. Supercritical fluids a. A supercritical fluid exists when the conditions exceed the critical point b. A gas normally liquefies at some point when pressure is applied i. A cylinder containing water vapor at 100 degrees celcious will form liquid water if 760 torr of pressure is applied ii. If the temperature is 110 degrees, the liquid phase does not form unti the pressure is 1075 iii. At 374 degrees, the liquid phase only forms at 1.655e5 torr iv. Aboce this temperature, no amount of pressure causes a distinct liquid phase to form v. Instead, as pressure increases, the gas becomes steadily more comperssed c. The highest temperature at which a distinct liquid phase can form is called the critical temperature d. The critical pressure is the pressure required to bring about liquefaction at this critical temp e. When the temp exceeds the crit temp, and the pressure exceeds the crit pressure, the liquid and gas phase are indistinguishable from each other, and the substance is in a state called a supercritical fluid 9. Heating Curve
a.
b. A material is heated or cooled at a constant rate under isobaric conditions over a broad temperature range c. Shows the SAME features as a horizontal line in a standard phase diagram, but in significantly more detail d. If we heat an ice cube initially at -25C at 1 atm, the temperature of the ice increases e. As long as the temp is below 0, the ice cube remains in the solid state f. When the temp reaches 0, the ice begins to melt g. Because melting is an endothermic process, the head we add at 0C is used to convert ice to liquid water, and the temperature remains constant until all the ice has melted General Chemistry Page 3
liquid water, and the temperature remains constant until all the ice has melted i. The enthalpy of vaporization is greater in magnitude than the enthalpy of fusion (length of the blue lines) because more energy is necessary to break the intermolecular forces (going from a liquid to gas) than is necessary to weak the intermolecular forces (solid to liquid) h. We can calculate the enthalpy change of the system for each segment of the heating curve i. The amount of heat needed to raise the temperature of segment AB, CD, and EF is calculated by the product of the specific heat, mass and temperature change ii. The greater the specific heat of a substance, the more heat we must add to accomplish a certain temp change iii. The slope of the line is inversely proportional to the heat capacity 1) The flatter the line, the greater the heat capacity i. The slope for each of the three phases are different, implying that the heat capacities for each of the three phases are different j. The heat capacity of the liquid Is the greatest of the three phases 10. Vapor Pressure a. About every liquid and solid (more so liquid) there is a finite amount of vapor formed when molecules at the surface layer escape b. A vapor is composed of gas particles that are in in equilibrium with the liquid phase, so they temporarily exist as gas, until they condense back into their more favorable phase c. "Force per unit area above the surface of a liquid exerted by molecules formed upon evaporation of the liquid" i. The vapor pressure of a liquid is simply the partial pressure exerted by the gas molecules formed by evaporation when it is in equilibrium with the gas molecules condensing back into the liquid d. The vapor pressure above a pure liquid depends on the temperature of the liquid and the Δhvaporization of the liquid
e.
f. It is difficult to measure the vapor pressure of an open system so we generally consider vapor pressure in an open system from a theoretical perspective, and apply values that have been determined previously in a closed system at known temperatures g. VAPOR PRESSURE IS INDEPENDENT OF THE SHAPE AND VOLUME OF THE CAINTINER i. The same amount of the liquid is vaporizing from each system per unit area of its surface, as long as the temperature of both systems is the same
1)
ii. The rate of vaporization is greater with the greater surface area, but the vapor General Chemistry Page 4
ii. The rate of vaporization is greater with the greater surface area, but the vapor pressure is still the same h. Vapor pressure increases as temperature increases but decreases as Δhvaporization increases i. As boiling point increases, the ability for a compound to vaporize decreases i. This means as the boiling point increases, less of the vapor is formed and consequently the vapor pressure decreases 11. Vapor Pressure Graphs a. Vapor pressure increases as the temperature of the solution increases, but NOT IN A LINEAR FASHION
i.
b. The graph CANNOT intersect the y-axis when the units of temp are kevelin and axis originates at zero c. For each substance, the vapor pressure curves sharply upward with increasing temperatur d. Relationship is given by the Clausis-Clapeyron equation i.
ii. e. The equation predicts that a graph of ln P versus 1/T should give a straight line with a slope equal to Δhvap/R 12. Boiling point a. The boiling point is the temperature above which a substance may not exist as a liquid OR the temperature at which the vapor pressure of a liquid is equal to the atmospheric pressure b. At reduced atmospheric pressure the boiling point of a liquid is lower than normal c. Under cases of increased pressure, the boiling point is higher than normal d. The greater the molecular mass of a compound, the harder it is to vaporize it, which means the greater the boiling point 13. Boiling point variations a. The boiling point of a compound can be altered either by varying the atmospheric pressure or by varying the intermolecular forces b. Boiling point increases as soluble impurities (such as salt) are added to solution i. The liquid has a greater tendency to stay a liquid 14. Rauolt's Law a. The vapor pressure above a solution of two or more miscible liquids depends on the mole fraction of each compound in solution b. A solution consisting of a volatile liquid solvent and a nonvolatile solute forms spontaneously because of the increase in entropy that accompanies their mixing c. If effect, the solvent molecules are stabilized in their liquid state by this process and this have a lower tendency to escape into the vapor state d. Therefore, when a nonvolatile solute is present, the vapor pressure of the solvent is lower than the vapor pressure of the pure solvent
General Chemistry Page 5
i.
e. The vapor pressure of a volatile solvent above a solution containing a nonvolatile solute is proportional to the solvents concentration in the solution i. ii. X = mole fraction of solvent iii. Po=vapor pressure of pure solvent f. Because molecules interact in both the liquid and gas phases, the vapor pressure relationship is not as linear as Raoult's equation i. If there is an overall increase in attractive forces in solution when the components are mixed, then vaporization, and thus vapor pressure, decreases ii. If there is an overall decrease in attractive forces in solution when the components are mixed, then vaporization, and thus vapor pressure increases 15. Distillation a. Used to remove a liquid from a solution b. To do so, the liquid must first be converted into vapor, and then the vapor is allowed to flow up a distilling column 16. Colligative properties a. Properties of a solution that are affected by the concentration of a soluble impurity, but not the KIND OR IDENTIY OF THE SOLUBLE IMPURITY b. As impurities are added to a solution, the solvent has a greater tendency to remain as a liquid c. When freezing saltwater, the freezing point of the salt solution continues to decrease as water freezes away from the solution because the molality of the impurity in the solution is increasing as water is removed. Same with boiling
i.
17. Boiling point elevation a. The increase in boiling point (and thus decrease in vapor pressure) is attributed to decreased surface area from which the liquid can evaporate and an increase in the intermolecular forces binding the liquid in solution General Chemistry Page 6
intermolecular forces binding the liquid in solution b. In the case of saltwater solution, water has stronger attraction to the ionic impurities than it does to other water molecules
i.
c. i. Kb is the constant for the solvent ii. I is the van't hoff factor (ionizavility constant--essentially the number of ions that form upon dissolving) iii. m is the molality d. Freezing point depression i. 18. WHEN SUGAR DISSOLBES IN WATER< THE I VALUE IS 1 a. IT DOES NOT FORM ANY IONS. REMAINS INTACT 19. Osmotic Pressure a. Water has a natural tendency to flow from solutions of higher water concentration to lower water concentration to reach equal concentrations b. Pressure causes water to flow, called osmotic pressure i. Force per unit area exerted by a solution throug osmosis across a smepiermeable memb rane ii. c. U-tubes are separated by a semi=oermeable membrane and allow nautral polymers like proteins to be separated by mass i. Only water can pass through the membranes ii. Water will continue to flow untill osmotic pressure equals the hydrostatic pressure, density*g*Δh
iii.
d. Once the water levels reach a fixed height, molarity can be determined, which can be converted to moles e. A given mass of protein was used, so the molecular mass is found by dividing the number of moles 20. Conductance a. Pure water does not conduct electrical current because there are no ions present in the solution General Chemistry Page 7
solution b. The specific conductance of an aqueous salt solution is directly proportional to the concentration of salt in solution c. Condosity is the molar concentration of an aqueous sodium chloride solution that has the same specific conductance as the aqueous salt solution d. Salts that form aqueous solutions capable of conducting electricity better than sodium chlroide solutions have a condosity greater than their molarity e. The greater the ratio of condosity to molarity, the better the salt at conducting electricity If I have a 2 M solution of KCl, what would we expect the condosity to be? Condosity is the concentration (Molarity) of an NaCl solution that will conduct electricity exactly as well as the solution in question. Since K is more metallic than Na, we know that it is a better conductor. Therefore, the condosity will be something greater than 2. From
General Chemistry Page 8
