Chimica inorganica

-------------------------------------------------THE CHANGES OF

STATE------------------------------------------------

Liquid State: Liquids have an own volume and surface;

Surface Tension: the tendency of liquid surfaces at rest to shrink into min

surface area possible.

Capillary Action: is the process of a liquid flowing in narrow spaces without

the assistance of, or even in opposition to, external forces like gravity. It occurs

because of intermolecular forces between the liquid and surrounding solid

surfaces. If the diameter of the tube is sufficiently small, then the combination

of surface tension (which is caused by cohesion within the liquid) and adhesive

forces between the liquid and container wall act to propel the liquid.

Evaporation ≠ Vaporization: type of vaporization which mostly occurs at

temperatures below the boiling point. Vaporization can change the state of

matter from a solid or liquid to a gas. During evaporation, the liquid state of

matter is turned directly into a gas. Evaporation is endothermic.

A liquid boils when its vapor pressure is equal to the external pressure. The

vapor pressure is the pressure of vapor at equilibrium with the liquid at

temperature T. Vapor pressure depends on T.

VOLATILITY: Liquids with high vapor pressure are called volatile.

- Volatile liquids have low boiling points.

- Liquid with low boiling point will boil faster than liquids with higher boiling

points.

- Much less energy (in form of heat) is required to break the intermolecular

bonds of a volatile liquid than those of liquids having higher boiling

points.

- Once enough energy is supplied to break apart the bonds between

molecules, the molecules are free to expand and escape the liquid

surface in the form of a gas.

Nonvolatile means that the solute itself has little tendency to evaporate

Evaporation ≠ Boiling: The evaporation is a surface phenomenon and

involves only the interface molecules. The boiling involves all the mass of the

liquid. A liquid boils when its vapor pressure is equal to the external pressure.

Evaporation is a slower process and boiling is faster. Boiling has a fixed

temperature evaporation any T above freezing.

Clausius–Clapeyron relation: On a pressure–temperature (P–T) diagram, the line

separating the two phases is known as the coexistence curve. The Clausius–

Clapeyron relation gives the slope

of the tangents to this curve. The

Clausius–Clapeyron relation

characterizes behavior of a closed

system during a phase change,

during which temperature and

pressure are constant by definition.

Dalton’s Law: For a mixture of gases in a container the total pressure exerted

is the sum of the pressure that each gas would exert if it were alone in the

same container at same temperature.

Physical property is a characteristic of a substance that can be observed or

measured without changing the identity of the substance. Physical properties

of matter include color, hardness, malleability, solubility, electrical

conductivity, density, freezing, melting, and boiling points.

Freezing point is the temperature at which a liquid changes to solid. Same

as melting point.

Melting point is the temperature at which a solid is converted to a liquid.

Melting point and freezing points thus occur at the same temperature because

the change of state involves the same two states (liquid-solid; solid-liquid). It is

the temperature at which a solid changes to a liquid or a liquid changes to a

solid. Evaporation occurs when water is lost from a substance. The

temperature at which the molecules of a liquid become gas is the boiling

point. Condensation occurs when water vapor is converted back to liquid.

Sublimation occurs when a solid is converted directly to a gas. An example of

sublimation is dry ice. It sublimes at -78°C and produces a gas or vapor.

Deposition occurs when a gas is converted directly to a solid.

-----------------------------------------------------

SOLUTIONS------------------------------------------------------------

Solution: is an homogenous system (liquid, solid, or gaseous) obtained by

mixing two or more substances mutually miscible. SOLVENT: most abundant;

SOLUTE: less abundant

Molarity (M): moles of solute per volume of solution (expressed in liters)

Molality (m): moles of solute per kilogram of solvent

MOLE FRACTION (XA): moles of the A component to total moles ratio. It is used

for GAS and LIQUID mixtures.

Temperature effects on solubility: For many solids dissolved in liquid water, the

solubility increases with temperature. The increase in kinetic energy that

comes with higher temperatures allows the solvent molecules to more

effectively break apart the solute molecules that are held together by

intermolecular attractions.

Pressure effects on solubility: The higher the pressure above a liquid, the more

gas that can be dissolved in that liquid, to a limit of course. An increase in

pressure increases solubility, whereas a decrease in pressure decreases

solubility.

Henry’s Law: the solubility of a gas in a liquid is directly proportional to the

partial pressure of the gas above the liquid.

Ideal Solution: The Raoult’s law is valid for ideal solutions, where the ∆Hsoln

is zero

Raoult’s law: the vapor pressure of a solvent above a solution is equal to the

vapor pressure of the pure solvent at the same temperature scaled by the mole

fraction of the solvent present

--------------------------------------------COLLIGATIVE

PROPERTIES----------------------------------------------------

Colligative Properties: is a property of a solution that depends only on the

number of solute particles dissolved in the solution and not on their identity.

- Salts are strong electrolyte

- Acids and bases are weak or strong electrolytes

- Sugars are non-electrolytes

van’t Hoff coefficient: is the ratio between the actual concentration of

particles produced when the substance is dissolved and the concentration of a

substance as calculated from its mass. As the solute concentration increases

the van’t Hoff factor decreases.

1. Vapor Pressure Lowering: determined by how easily its molecules are

able to escape the surface of the liquid and enter the gaseous phase.

When a liquid evaporates easily, it will have a relatively large number of

its molecules in the gas phase and thus will have a high vapor pressure.

Liquids that do not evaporate easily have a lower vapor pressure. The

vapor pressure of a pure solvent is greater than the vapor pressure of a

solution containing a non-volatile liquid. This lowered vapor pressure

leads to boiling point elevation.

2. Boiling-point elevation: The difference in temperature between the

boiling point of the pure solvent and that of the solution.

Since the vapor pressure of the solution is lower, more heat must be

supplied to the solution to bring its vapor pressure up to the pressure of

the external atmosphere.

The magnitude of the boiling point elevation is directly proportional to

molality of the solution.

The equation is: ΔTb=Kb x m

The proportionality constant Kb is molal boiling-point elevation constant. It

is a constant that is equal to the change in the boiling point for a 1-molal

solution of a nonvolatile molecular solute.

3. Freezing Point Depression: the difference in temperature between the

freezing point of the pure solvent and that of the solution. The figure

below shows the phase diagram for a pure solvent and how it changes

when a solute is added to it. The solute lowers the vapor pressure of the

solvent resulting in a lowering of the freezing point of the solution

compared to the solvent. When a pure solvent freezes, its particles

become more ordered as the intermolecular forces that operate between

the molecules become permanent.

By dissolving a solute into the liquid solvent, this ordering process is

disrupted. As a result, more energy must be removed from the solution in

order to freeze it, and the freezing point of the solution is lower than that

of the pure solvent.

The magnitude of the freezing point depression is directly proportional to the

molality of the solution. The equation is: Δ

T_f=Kf x m

The proportionality constant Kf , is called the molal freezing-point

depression constant . It is a constant that is equal to the change in the

freezing point for a 1-molal solution of a nonvolatile molecular solute.

4. Osmotic Pressure: Osmosis is the spontaneous net movement or

diffusion of solvent molecules through a selectively permeable

membrane from a region of high water potential (region of lower solute

concentration) to a region of low water potential (region of higher solute

concentration), in the direction that tends to equalize the solute

concentrations on the two sides. Osmotic pressure is defined as the

external pressure required to be applied so that there is no net

movement of solvent across the membrane.

-------------------------------------------CHEMICAL

EQUILIBRIUM-------------------------------------------------------

Chemical equilibrium: Dynamic condition of a system in which the rate of the

forward reaction is equal to the rate of the reverse reaction. At the chemical

equilibrium the concentration of all reactants and products remains constant

with time.

- The system must be closed, meaning no substances can enter or leave

the system.

- Equilibrium is a dynamic process. Even though we don’t necessarily see

the reactions, both forward and reverse are taking place.

- The rates of the forward and reverse reactions must be equal.

- The amount of reactants and products do not have to be equal. However,

after equilibrium is attained, the amounts of reactants and products will

be constant.

Law of mass action (equilibrium law): the principle that (at chemical

equilibrium) in a reversible reaction the ratio of the rate of the forward reaction

to the rate of the reverse reaction is a constant for that reaction.

Equilibrium positions: Each set of equilibrium concentration is called

equilibrium position

Le Chatelier's Principle: a system at equilibrium will adjust to relieve stress

when there are changes in the concentration of a reactant or product, the

partial pressures of components, the volume of the system, and the

temperature of reaction.

The effect of a change in pressure: There are three ways to change the

pressure of a constant-temperature reaction system involving gaseous

components:

- Add or remove a gaseous reactant or product: Adding or remove a

gaseous reactant or product changes the concentrations. If the

concentration of reactant or product is increased, the system will shift

away from the side in which concentration was increased (i.e. if the

concentration of reactants is increased, the system will shift toward the

products. If more products are added, the system will shift to form more

reactants). Conversely, if the concentration of reactant or product is

decre