CHEM 1220 - Midterm 1

when does a solution form?

when two or more substances mix

What two factors does the ability of substances to form solutions depend on?

1) The natural tendency of substances to mix and spread into larger volumes when not restrained in some way and 2) the intermolecular forces that hold molecules together in both pure substances and solutions.

What type of process is mixing gases?

Spontaneous

What is entropy?

A measure of randomness or disorder

How does entropy influence the formation of solutions?

Mixing gases increases disorder which constitutes an increase in entropy. An increase in entropy then increases the favorableness of a solution forming.

What are the 3 kinds of intermolecular interactions involved in solution formation?

solute-solute, solvent-solvent, and solute-solvent

What is the enthalpy change of the solute and solvent?

Both components are endothermic because both require an input of energy to separate the molecules.

What is the enthalpy change of the mix of solute and solvent?

exothermic

In order for a solution to form, what must be true about the three components?

The magnitudes of delta Hmix must be comparable to or greater than the delta H of solutes plus solvents.

What is the generalization about solubility?

“like dissolves like”

* polar solute dissolves polar solvent best
* non polar solute dissolves non polar solvent best

Why do non polar liquids (such as hydrocarbons) tends be insoluble in liquids?

The attraction between polar water molecules and the non polar hydrocarbon molecules is not strong enough (no hydrogen bonding and low/weak dipole moments) to allow the formation of a solution.

Is the endothermic solution process favorable? Would it spontaneously occur?

No

What is one way to increase the solubility in H2O?

Increase the number of polar groups

What is one way to enhance the solubility in an organic solvent?

Increase the amount of carbon chains

Why does the solubility of alcohols decrease in water as the length of the carbon chain increases?

As the carbon chain increases, the polar -OH group has less of an impact and the molecule acts more like a hydrocarbon.

Solution formation is favored by…

an increase in entropy and a decrease in enthalpy

What is crystallization?

a process in which molecules, ions, or atoms come together to forma crystalline solid (opposite of a solid dissolving in a solvent to form a soln)

Solubility

The amount of solute needed to form a saturated soln in a given quantity of solvent

Saturated

a solution in EQ with undissolved solute

Unsaturated

solution that contains less solute than needed to form a saturated solution

Supersaturated

solution that contains more solute than an equivalent saturated solution (very difficult to achieve)

Which attractions must be the strongest in order for the solubility of a solute to be the greatest?

The stronger the attractions between the solute and solvent molecules, the greater the solubility of the solute in that solvent

Comparing a gas with a larger molar mass and a smaller molar mass, which one will have the highest solubility in water?

the gas with the larger molar mass

What does Henry’s Law mean?

The law means that the solubility of a gas, @@in a liquid solvent@@, is directly proportional to the pressure of the gas.

What is the equation for Henry’s Law?

Sgas = k x Pgas

What is the difference between the solubility solid solutes in water vs solubility of gases with increasing temperature?

As temperature increases, the solubility of solid solutes in water increases but decreases for gases.

What does miscible mean?

mix in all proportions

What is a colligative property

molality

moles of solute/kg of solvent

When is molality better to use than molarity?

Molality is better to use when a solution is being used over a range of temperatures because molality uses the mass of the solvent which doesn’t change over time (only volume changes due to temp)

stopped at 13.3-13.5 pre lecture

start with colligative properties