Flashcards in General Chemistry- Solutions Deck (150)
What are solutions?
Homogeneous (the same throughout) mixtures of two or more substances that combine to form a single phase, usually the liquid phase.
What are mixtures?
Gases "dissolved" into other gases can be thought as solutions, but are more properly defined as mixtures because gas molecules do not interact all that much chemically.
Can all solution be considered mixtures? Can all mixtures be considered solutions?
All solution are considered mixtures, but not all mixtures are considered solutions.
What do solutions consist of?
A solute and solvent
What is a solute?
Something dissolved or dispersed in a solvent.
(NaCl, NH3, C6H12O6, CO2)
What is a solvent?
The component of the solution that remains in the same phase after mixing. If the two substances are already in the same phase, the solvent is the component present in greater quantity. If the two same-phase components are in equal proportions in the solution, then the component that is more commonly used as a solvent in other context is considered the solvent.
What do solute molecules do in a solvant?
Move freely in the solvent and interact with it by way of intermolecular forces such as ion-dipole, dipole-dipole, or hydrogen bonding. Dissolved solute molecules are also relatively free to interact with other dissolved molecules of different chemical identities.
What is solvation?
The electrostatic interaction between solute and solvent molecules.
What is another name for solvation?
Dissolution, and when in water Hydration
What is involved in solvation?
Solvation involves breaking intermolecular interactions between solute molecules and between solvent molecules and forming new intermolecular interactions between solute and solvent molecules together.
When is a solvation exothermic?
When the new interactions are stronger than the original ones
What are examples of exothermic processes?
The dissolution of gases into liquids, such as CO2 into water, because the only significant interactions that must be broken are those between water molecules.
What does Le Chatelier's principle tell us?
That lowering the temperature of a liquid favors solubility of a gas in the liquid.
When is a solution endothermic?
When the new interactions are weaker than the original ones
Most dissolutions are exothermic or endothermic?
What are examples of endothermic dissolutions?
Dissolving ammonium nitrate or sugar into water
What must be added to an endothermic dissolution? Why?
Energy must be added because the new interactions between the solute and solvent are weaker than the original interactions between the solute molecules.
What happens when the overall strength of a endothermic solution is equal to the overall strength of the original interaction?
The overall enthalpy change for the dissolution is close to zero. These types of solutions approximate the formation of an ideal solution, for which the enthalpy of dissolution is equal to zero.
What contributes to the sponteneity of dissolution?
Gibbs free energy
What always increases upon dissolution at constant pressure and temperature?
Entropy always increases
Sponteneous processes in dissolution are associated with what in regards to free energy? Nonspontaneous?
Decrease in free energy
Nonspontaneous process with increased free energy
Is the formation of ion-dipole interactions exothermic or endothermic?
Why is the dissolution of table salt in water endothermic?
The magnitude is slightly less than the energy required to break the ionic bonds and hydrogen bonds. As a result the overall dissolution of table salt inot water is endothermic and favored at high temperatures.
What is entropy?
The degree to which energy is dispersed throughout a system or the amount of energy distributed from the system to the surroundings at a given temperature.
What is another way to understand entropy?
The measure of molecular disorder, or the number of energy microstates available to a system at a given temperature.
What does it mean when you say ions have a greater number of energy microstates?
The ions, freed from their lattice arrangement, have a greater number of energy microstates available to them (in simpler terms, they are freer to move around in different ways).
If a solid dissolves in a liquid forming a liquid, what happens to the solid's entropy and what happens to the liquids entropy?
A solid's energy is more distributed and the entropy increases
Liquid becomes more restricted in its movements, microstates decrease and entropy decrease.
How do you determine the overall entropy of a solution?
The increase in the entropy experienced by the dissolved sodium chloride is greater than the decrease in the entropy experienced by the water, so the overall entropy change is positive.
What is solubility?
The maximum amout of that substance that can be dissolved in a particular solvent at a given temperature.