Part 1 Definitions

Question 1

What is a solution? What is the solute like in the solution?

Answer 1

Homogenous mixture of 2 or more pure substances

In a solution, the solute is dispersed uniformly throughout the solvent. Extremely important because it helps us predict how the solution behaves and allows us to perform calculatio

Question 2

What is the solute definition vs solvent definition?

What is solubility?

Answer 2

solute - substance being dissolved

solvent - present in greater amount

Solubility - amount of a substance that dissolves in a given amount of solvent (usually H20)

Question 3

What are some common types of solutions?

Answer 3

Air in gaseous solution == solute gas == solvent gas

club soda == solute gas == solvent liquid

vodka == solute liquid == solvent liquid

seawater == solid solute == solvent liquid

brass == solute solid == solvent solid

Question 4

3 types of homogenous mixture and their consequences

Answer 4

1. solids in liquids (hydration vs solvation)

Solvation, is the process of attraction and association of molecules of a solvent with molecules or ions of a solute.

Hydration is the process of attraction and association of molecules of water with molecules or ions of a solute

2. liquids in liquids (miscible vs immiscible)

Miscible substances fully mix in all proportions

Immiscible substances never fully mix in any proportions

3. gases in liquids (Henry’s Law)

(concentration of dissolved gas ) = (partial pressure of gas) x (solubility coefficient)

Question 5

What is hydration and solvation?

Question 6

What is Henrys Law?

Answer 6

Question 7

What is miscible vs immiscible?

Question 8

What is unsaturated and saturated and supersaturated?

Answer 8

Unsaturated: contains less than the maximum amount of solute

Saturated: contains the maximum amount of solute

Question 9

What is equilibrium saturation?● Equilibrium: dissolution and crystallization occur at opposite rates

Answer 9

Equilibrium: dissolution and crystallization occur at opposite rates

Question 10

What determines solubility?

Answer 10

Entropy (tendency towards mixing from disorder)

Intermolecular Forces

Affect but do not determine: Temperature and Pressure

Question 11

How does entropy determine solubility?

Answer 11

A thermodynamic quantity representing the unavailability of a system’s thermal energy for conversion into mechanical work, often interpreted as the degree of disorder or randomness in the system.

DISORDER

Question 12

How do IMFs determine solubility?

Answer 12

The intermolecular forces between solute and solvent particles must be strong enough to compete with those between solute particles and those between solvent particles.

Question 13

How do solutions form?

Answer 13

As a solution forms, the solvent pulls solute particles apart and surrounds, or solvates, them.

Question 14

What are the relative interactions that determine if a solution forms?

Answer 14

Question 15

Describe salt in solution?

Answer 15

If an ionic salt is soluble in water, it is because the ion- dipole interactions are strong enough to overcome the lattice energy of the salt crystal.

Question 16

What are the 3 steps that affect the energetics of solution?

Answer 16

3 steps that affect the energetics of solution:

1. Separation of solute particles,
2. Separation of solvent particles,
3. New interactions between solute and solvent.

Question 17

What is Hess’s Law?

Answer 17

Question 18

What is Hess’s Law the sum of?

Answer 18

Hess Law: the overall enthalpy change in solution formation, called the enthalpy of solution (ΔHsoln) is the sum of the changes in enthalpy for each step:

deltHsoln = deltaHsolute + deltaHsolvent + deltaHmix

Reminder: Enthalpy (H) is the sum of the internal energy (U) and the product of pressure and volume (PV). Has units of kJ/mol.

H = E + PV

Question 19

What parts of Hess’s Law (deltaHsoln) are positive or negative (endothermic or exothermic) and why?

Answer 19

deltaHsolute

endothermic (+) AND always > 0

requires energy to break interactions in solute

deltaHsolvent

endothermic (+) AND always > 0

requires energy to break interactions in solvent

deltaHmix

exothermic (-) AND always < 0

releases energy to form new interactions (solute + solvent)

Question 20

What are the 2 possible outcomes of heat?

Answer 20

exothermic releases heat against increasing energy

endothermic absorbs heat against increasing energy

Question 21

What is the third reaction of a solution from Hess’s Law?

Answer 21

Question 22

What happens to the Hess Law equation for deltaHsoln to be equal to about 0?

Answer 22

if the sum of the endothermic terms is approximately equal in magnitude to the exothermic term, then deltaHsoln is about zero

deltHsolute + deltHsolvent ~ deltaHmix

Question 23

Why do endothermic processes occur?

Answer 23

Because of entropy!

Question 24

Do both endothermic and exothermic process occur at the same time in solution?

Answer 24

Yes, both of these are spontaneous because of entropy

Question 25

What effect does entropy have on energy of the system?

Answer 25

Increasing the disorder or randomness (entropy) of a system tends to lower the energy of the system. So even though enthalpy may increase, the overall energy of the system can still decrease if the system becomes more disordered.

Question 26

What is the heat of hydration? When is it used? What is it derived from?

Answer 26

Heat of hydration is emitted when 1 mole of gaseous solute ions is dissolved in water. =heat of solvent + heat of mix used when dissolving ionic compounds in water **Heat of hydration** derived from heat of solvent and heat of mix **Heat of solute** is the sum of the negative of the lattice energy

Question 27

How to calculate the enthalpy change of solution (ΔHsol) for calcium fluoride (CaF2).

Answer 27

1. balance the equation 2. multiply heats by numbers based on number of moles in balance equation

Question 28

How do you calculate the lattice enthaply?

Answer 28

Heat of solute is the sum of the negative of the lattice energy Use equation to calculate

Question 29

What does it mean if something disappeared?

Answer 29

Just because something “disappeared” in solution doesn’t mean that it dissolved! Dissolution is a physical change, if we remove the solvent (by evaporation) we can obtain the solute again.

Question 30

Explain concept of like dissovles like

Answer 30

Polar substances tend to dissolve in polar solvents. Non-polar substances tend to dissolve in non-polar solvents. Example Glucose (which has hydrogen bonding) is very soluble in water, while cyclohexane (which only has dispersion forces) is not.

Question 31

How to predict whether each of the following solvent is miscible or immiscible with water?

Answer 31

Water is polar, so it is most miscible with substances that are polar and have the same IMFS

Question 32

How does temperature affect solubility (solids in liquids)?

Answer 32

Generally, the solubility of solid solutes in liquid solvents increases with increasing temperature.

Question 33

How does temperature affect solubility (gases in liquids)?

Answer 33

• The opposite is true of gases. o Carbonated soft drinks are more bubbly if stored in the refrigerator. o Warm lakes have less O2 dissolved in them than cool lakes.

Question 34

How does pressure effect solubility of gases, liquids, solids? How do you quantify solubility?

Answer 34

* Pressure plays a role in the solubility of gases, but not so much in liquids and solids, why? Pressure doesn’t affect the volume of solids and gases. * Associate pressure with less volume. PV = nRT Quantify gas solubility using Henry's Law Sgas = Kh x Pgas

Question 35

How do you quantify gas solubility?

Answer 35