O.1 Flashcards
Dissolving processes
How are ions in an ionic solid held together?
By their opposite electrical charges. Each cation attracts several anions and vice versa.
What is called when a large number of ions are arranged in fixed positions, held together by electrostatic forces?
Giant ionic lattice.
In ionic lattice, which two type of forces compete, and which one is always greater?
Attraction and repulsion. But overall attractions are always greater and therefore the lattice is held together.
What are two properties of ionic solid as a result of its strong electrostatic attraction?
They are hard and have high melting and boiling points.
What happens to ions in a ionic substance when they dissolve in water?
Ions become surrounded by water molecules and spread out through the water.
What is the attraction between water molecules and ions known as?
Ion-dipole interaction.
Which part of the water molecule interacts with the cation?
The O.
Which part of the water molecule interacts with the anion?
The two Hs.
Can ion-dipole interactions be multilayers?
Yes.
How many water molecules interact with each ion in the first layer?
Four.
Ions in ionic substances are said to be what once they are dissolved in water?
They are separated and behave independently of each other.
What are water molecules that surround an ion known as that makes ions hard to move?
A solvation shell.
Are all ionic substances soluble in water?
No.
What is important in deciding whether an ionic substance will dissolve?
The energy changes involved.
What bonds must be broken before ionic substance can dissolve and spread out in the solution?
The electrostatic bonds between ions in the lattice must be broken to separate the ions.
Separating the ions by breaking electrostatic bonds is an example of what type of energy change?
Endothermic. So energy is required.
What enthalpy change measures the strength of ionic attractions in a lattice?
Lattice enthalpy.
What is the symbol representation of lattice enthalpy?
∆H(LE), where LE refers to lattice.
What is the definition of lattice enthalpy?
The enthalpy change when one mole of ionic solid is formed by the coming together of the separate ions.
What physical state changes are involved in the lattice enthalpy?
From ions in gaseous states to a lattice in solid state.
What sign does lattice enthalpy always have?
- negative, lattice enthalpies are always exothermic, because it is a bond making process.
The amount of energy you’ll have to put into breaking a lattice is equivalent to what value?
-∆H(LE), this becomes a positive value, as breaking bonds is an endothermic process and require an energy input.
What are two factors lattice enthalpies depend on?
- Size of ions
- Charge of ions
As the ionic charges increase, what happens to the value of the lattice enthalpy?
It becomes more exothermic.
As the ionic radii, increase, so ion gets bigger, what happens to the value of lattice enthalpy?
It becomes more endothermic.
So, bigger ionic charges and smaller ionic radii means a more exothermic lattice enthalpy. How can these two factors be summaries to one?
The higher the charge density, the more exothermic the lattice enthalpy.
Large negative lattice enthalpy can suggest what about a substance’s solubility?
They are usually insoluble.
When a ionic solid is placed in water, where does ion-dipole interaction happen first?
On the surface, where surface ions become separated and surrounded by water molecules.
When an ion is in solution, and surrounded by water molecules, what is it said to be?
Hydrated.
What impact will high charge density of an ion have on the size of the hydrated ion in solution?
The higher the charge density, the bigger the hydrated ion will be because the more water molecules will be attracted.
When ion-dipole bond forms, what energy change is involved?
Exothermic, the process releases energy.
Does all the energy released through the forming of ion-dipole bonds go into breaking electrostatic bonds in the lattice?
No, some also go on to break the strong hydrogen bonding between water molecules.
What enthalpy change measures the strength of attraction between ions and water molecules?
Enthalpy change of hydration.
What is the symbol representation of the enthalpy change of hydration?
∆H(hyd), where hyd refers to hydration.
What is the definition of the enthalpy change of hydration?
The enthalpy change for the formation of a solution of ions from one mole of gaseous ions.
What physical state changes are involved in the enthalpy change of hydration?
From ions in gaseous state to ions in solution.
What sign does the enthalpy change of hydration always have?
- negative, hydration is exothermic and energy is released.
What are two factor enthalpy change of hydration depends on?
- Ionic charges
- Ionic radii
As the charge density of ion increase, what happens to the value of the enthalpy change of hydration?
It gets more exothermic.
What enthalpy change is used when the solvent is not water?
Enthalpy of solvation, ∆H(solv).
What enthalpy change can be derived from finding the difference between the enthalpy change of hydration and the lattice enthalpy?
The enthalpy change of solution.
What is the symbol representation of the enthalpy change of solution?
∆H(solu), where solu refers to solution.
What is the definition of the enthalpy change of solution?
The enthalpy change when one mole of solute dissolves to form a very dilute solution.
How can the enthalpy change of solution be found?
It can be measured experimentally.
What is the equation that enables you to find the enthalpy change of solution from the lattice enthalpy and enthalpy changes of hydration?
∆H(solu) = ∆H(hyd, cation) + ∆H(had, anion) - ∆H(LE)
When is the enthalpy change of solution negative?
When the sums of enthalpy changes of hydration is bigger than the lattice enthalpy.
When the enthalpy change of solution is negative, and therefore the dissolving process is exothermic, what does this mean about the solubility of the substance?
The substance normally dissolves, giving out some energy is the process.
When is the enthalpy change of solution positive?
When the sums of enthalpy changes of hydration is smaller than the lattice enthalpy.
When the enthalpy change of solution is a large positive value, so the process of dissolving is very endothermic, what does this mean about the solubility of the substance?
The substance does not dissolve, because the process requires more energy and is energetically unfavorable.
When the enthalpy change of solution is slightly positive, so a little bit endothermic, what does this mean about the solubility of the substance?
The substance will normally still dissolve, despite the process seems to be energetically unfavorable.
