Ch. 9: Solutions (Complete) Flashcards
defn: solutions
homogeneous mixtures of two or more substances that combine to form a single phase (usually the liquid phase)
NOTE: almost all reactions in living organisms take place in solutions
the MCAT focuses mostly on solids dissolved in aqueous solutions, but combinations of the three phases of matter can also form solutions, give 3 examples.
- gases dissolved in liquids (carbonating soda)
- liquids dissolved in other liquids (ethanol in water)
- solids dissolved in other solids (metal alloys)
why are gases “dissolved” in gases considered as mixtures more than as solutions?
gas molecules do not interact all that much chemically
what is the relationship between mixtures and solutions?
all solutions are mixtures
not all mixtures are solutions
defn: solute
the part that is dissolved or dispersed in a solvent
what are 4 common examples of a solute?
- NaCL
- NH3
- C6H12O6
- CO2
defn: solvent
the component of the solution that remains in the same phase after mixing
what are 3 common examples of a solvent?
- H2O
- Benzene
- Ethanol
if the two substances are already in the same phase, how do you determine which is the solvent and which is the solute?
the solvent is the component present in greater quantity
how do you determine which is the solvent and which is the solute if the two substances are already in the same phase and are in equal proportions in the solution?
the component that is more commonly used as a solvent in other contexts is considered the solvent
how do solute molecules interact with the solvent?
solute molecules move about freely in the solvent and interact with it by way of intermolecular forces such as ion-dipole, dipole-dipole, or hydrogen bonding
why do chemical reactions occur easily in solution?
because dissolved solute molecules are also relatively free to interact with other dissolved molecules of different chemical identities
defn + aka: solvation
the electrostatic interaction between solute and solvent molecules
involves breaking intermolecular interactions between solute molecules and between solvent molecules and forming new intermolecular interactions between solute and solvent molecules together
aka: dissolution
what is solvation referred to as when water is the solvent?
hydration
when is solvation exothermic?
is this favored at high or low temperatures?
example?
when the new interactions are stronger than the original ones
- favored at lower temperatures
- ex: dissolution of gases into liquids (such as Co2 in to water)
explain why the dissolution of gases into liquids is exothermic
because the only significant interactions that must be broken are those between water molecules
CO2, as a gas, demonstrates minimal intermolecular interaction
when is solvation endothermic? why?
is this favored at higher or lower temperatures?
2 examples?
when new interactions are weaker than the original ones
because the new interactions between the solute and solvent are weaker than the original interactions between the solute molecules and between the solvent molecules, energy (as heat) must be supplied to facilitate the formation of these weaker, less stable interactions
favored at higher temperatures
ex: dissolving ammonium nitrate or sugar into water
are most dissolutions endothermic or exothermic?
endothermic
defn: ideal solution
approximated by: overall strength of the new interactions is approximately equal to the overall strength of the original interactions
what is the enthalpy of dissolution for an ideal solution?
0
what are the three factors that affect the spontaneity of dissolution?
- enthalpy change for solute and solvent
- entropy change for solute and solvent (at constant temperature and pressure, entropy always increases upon dissolution)
- change in Gibbs free energy (spontaneous (deltaG < 0); nonspontaneous (deltaG > 0))
at constant temperature and pressure, does entropy increase or decrease for dissolution?
increases
define entropy in terms of microstates (entropy as a measure of molecular disorder)
entropy = the number of energy microstates available to a system at a given temperature = the molecules’ ability to move around in different ways
defn: solubility
the maximum amount of that substance that can be dissolved in a particular solvent at a given temperature