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46 Cards in this Set
- Front
- Back
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What are the two general factors that determine a substance's ability to form a solution?
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Its intermolecular forces, and the natural tendency of substance to spread into larger volumes when not restrained in some way (like salt in water).
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Why does a solute dissolve in a solvent?
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Because the forces between the solute and solvent are much greater than the solute-solute solvent-solvent forces.
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Interactions between solute and solvent molecules are called...
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Solvation
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Interacations between solute and solvent particles when water is the solvent are called...
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Hydration
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What are each of the ΔHs (H1, H2, and H3) standing for in the ΔH(soln) equation? (ΔH(soln) = ΔH1 + ΔH2 + ΔH3)
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Breaking the solute-solute particles, the solvent-solvent particles, and forming the solute-solvent interacitons.
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ΔH1 and ΔH2 are always endothermic because they require the breaking of interactions between solute or solvent particles. What is different about ΔH3?
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It is the formation of attractions between the solute and solvent molecules and it is always exothermis and requires no input of energy, but rather releases it.
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T/F: Because exothermic reactions tend to occur spontaneously, if ΔH(soln) is too high then a solution will not form.
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True
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Discuss the allowable magnitudes of ΔH1 and ΔH2 compared with ΔH3.
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H3 (the solute-solvent exothermic reaction) must be a large enough negative to compete with the positive, endothermic H1 and H2. If not, the solution will not form, which is why ionic NaCl will not dissolve in very polar substances like gasoline, bc the weak solute-solvent forces are not enough to overcome the covalent bonds in gasoline.
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T/F: Processes in which the energy content of the system decreases tend to occur spontaneously.
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True
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Why does removing the barrier between two liquid substances and allowing them to reach equilibrium increase the randomness of the system?
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Bc now the particles are much less uniform in the mixture and because they now occupy a much larger volume
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T/F: Processes occuring at a constant temperature in which the randomness (entropy) of the system increases tend to occur spontaneously, even if they are endothermic, as in the ice-pack reaction.
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True
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T/F: Spontaneous processes tend to occur at lower enthalpy and increased entropy.
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True
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What is the difference between a solution that be evaporated to get the original solute back and one that cannot?
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The one than cannot evaporate to the original solvent has had an actual CHEMICAL reaction, changing the solvent to a different compound altogether. It didn't just have a physical reaction of mixing or dissociating.
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The opposite of the solution/dissociation process in which dissociated solute particles reattach to the original solid itself is called...
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Crystallization
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A solution that is in equilibrium with the undissolved solid is said to be...
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Saturated
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T/F: Given that excess solute is present, "solubility" is the maximum amount of solute that will dissolve in a given amount of solvent at a specified temperature.
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True
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If we dissolve less solute than is needed to form a saturated solution, then the solution is....
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Unsaturated
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Why does supersaturation occur? (Being able to dissolve more than the actually solubility of that solute in a solvent)
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Bc the solubility of a solute into a solvent increases with temp, and when the solution is cooled it will still be unsaturated.
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Why do substances tend to randomly mix?
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Because they are tending toward more randomness or increased entropy
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The stronger the attractions are between solute and solvent molecules, the greater the solubility. Discuss this in terms of van der Waals forces.
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A nonpolar gas with more mass has more dispersion forces and is thus usually more soluble. Even more soluble than this, though, are polar substances which have stronger dipole-dipole forces.
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Pairs of liquids that mix in all proportions (such as water and very polar, hydrogen bonding acetone) are called _, and those that do not dissolve in one another are called _.
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Miscible; immiscible
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Why would ethanol (CH3CH2OH) be miscible in water?
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Bc it is polar and can form hydrogen bonds with its hydroxyl group on the end.
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What happens as a hydrocarbon alcohols gain more carbons and attached H's?
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They become less polar, less soluble in water, and more soluble in polar substances.
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T/F: Substances with similar intermolecular attractive forces tend to be soluble in one another
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True ("like dissolves like")
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T/F: The solubility of the gas increases in direct proportion to its partial pressure above the solution
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True
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Why does the CO2 (carbonated stuff) eventually escape from soda and leave it flat when opened?
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Bc in a bottle the partial pressure of CO2 above the solvent is high. When the bottle is opened, the partial pressure of CO2 is decreased, and thus of course the solubility decreases, and the CO2 escapes the drink.
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What is true about the solubility of solids in water with increasing temperature?
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Solid's solubility in water increases with increasing temperature because temperate increases disorder of the rigid solids
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(Such as the CO2 in soft drinks) Why does the solubility of gases in water decrease with increasing temperature?
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Because for gases, increasing temperature means even more instability and so the gas molecules do not stay trapped in water.
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What is the main difference between molarity and molality?
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Molarity depends on volume of the entire solution, while molality depends on mass only of the solvent.
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Why is molality often the unit of choice when considering solutions over varying temperatures?
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Because molality depends on MASS of the solvent, and mass never changes with temperature, whereas molarity depends on volume of the solution which definitely changes with temperature.
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A decrease in freezing point, an increase in boiling point, vapor-pressure reduction, and osmotic pressure are all...
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Colligative properties
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What are colligative properties?
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Properties of solutions that ONLY depend on the number of molecules, not at all on the type of molecule
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What is a NONvolatile substance?
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One that exerts no vapor pressure at equilibrium
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When examining the vapor pressure of pure substances versus the same substances as solvents in solutions, and when a NONvolatile (no vapor pressure) substance is added as a solute, what happens to the vapor pressure of the solution?
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Bc the solute is nonvolatile, the vapor pressure of the solution/system decreases with the amount of nonvolatile solute added.
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The relationship above is explained by what law?
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Raout's law, which says that the vapor pressure of a solution = the product of: the mole fraction of the SOLVENT times the vapor pressure of the SOLVENT.
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Why is the boiling point of a solution containing a nonvolatile solute higher than that of the pure solvent?
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Bc the nonvolatile solute lowers the vapor pressure, and the NORMAL BOILING POINT is the boiling point at vapor pressure 1 atm. If the vapor pressure is lowered, however, then the boiling point will need to be higher to compensate.
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T/F: Because NaCl dissociates in water, the boiling point elevation of a 1m aqueous solution of NaCl is approx (2m)(.51°C/m) = 1°C, twice as large as the boiling point of a solution with something like glucose that doesn't dissociate.
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True
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In contrast, the freezing point of a solution is....
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Lower than that of the pure solvent
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"The net movement of solvent particles is always toward the solution with the HIGHER solute concentration" (in order to dilute it) is called...
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Osmosis
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The pressure required to prevent osmosis by a pure solvent is called _ and is indicated by...
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Osmotic pressure: ∏ (capital pi)
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Open-chain hydrocarbons are called...
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Aliphatic
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How can you tell just by the formula of an organic compound that it is an alkENE?
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There are always twice as many hyrdogens as carbons in the hydrocarbon: C(n)H(2n)
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What is the difference between 1 and 2 butene?
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They each have 4 carbons and at least one single bond, but in 1 butene the single bond is touching the first carbon, and in 2 butene it is touching the second as its lowest carbon.
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What is the rule for numbering an organic compound based on its carbons?
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Always try to make the double bond have the lowest Carbon number possible, even if that means counting from right to left.
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How can you recognize an alkYNE?
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Double the number of H's and subtract them by two to get the number of carbons = they have triple bonds
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If you have a regularly-named hyrdocarbon but you find out its in a circle, what prefix do you add?
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Cyclo (sometimes, not on benzene)
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