Solids and Liquids

Kinetic-Molecular Theory of Matter

Gas Solid Liquid

Kinetic-Molecular Theory

According to the Kinetic-Molecular Theory, the state of a substance at room temperature depends on the strength of the attraction between its particles.

Gas – weakLiquid-moderateSolid- strong

Kinetic Theory of Gases

Particles are independent from one another and move in straight lines.

Change of direction occurs only when particles strike each other or container.

Movement is random.

Kinetic Theory of Liquids

Particles much closer together.

Particles do not act independently from one another.

Have a vibratory type of motion.

Movement occurs when particles shift between the spaces of particles.

Kinetic Theory of Liquids

Kinetic Theory of Solids

Particles close together and do not act independently.

Particles occupy a relatively fixed position in relation to surrounding particles.

Vibration around a fixed point.

Properties of Solids

All true solid substances are composed of crystals.

Solids have low kinetic energy.

They have a definite volume and assume their own shape.

High densities and Melting points.

Crystal Structure Crystals are made from

small units called unit cells. These units are repeated

over and over again as the crystal grows.

The arrangement of these unit cells is determined by the bonds between the particles.

Early crystallographers classified crystals on the basis of their external shapes into seven crystal systems.

Crystal SystemsEX: Cubic Hexagonal

Unit cell

Allotropes Allotropes are different chemical states of same element in same physical state.

EX: Allotropes of carbon are diamonds and graphite.

Diamond: pyradmidal lattice held together by strong covalent bonds.

Graphite: layers of hexagonal units held together by weak forces.

Amorphous Substances

Amorphous substances, sometimes referred to as amorphous solids, appear to be in the solid state but have no crystal structure.

Glass is the best known example. Glass does not have a sharply defined

melting point (like other solids). Viscosity (resistance to flow) is used

to describe the texture of glass. High viscosity, high resistance to flow

(thick).

AMORPHOUS CRYSTALLINE SOLID

Properties of Liquids

Liquids occupy a definite volume but they do not have their own shape.

Liquid movement is considered fluid. Bodies of nonmoving liquids are always

flat on top.

Surface Tension and Capillary Action

A liquid molecule is attracted to other liquid molecules. This is called cohesion.

Surface tension is a function of cohesion.

A liquid molecule can also be attracted to other materials. This is called adhesion.

Capillary action is a function of adhesion and cohesion.

Surface Tension

Surface tension is the force at the surface of a liquid due to the cohesive forces of the molecules of liquid for each other.

A paper clip will “float” on water despite having a higher density.

The cohesive forces of the water molecules keep the paper clip from pushing through.

An insect takes a walk on water

Surface Tension

Surface Tension

Surface tension can also be affected by adhesion.

Example: Adhesive forces of the liquid molecules for the walls of the container.

The smaller the container the greater the cohesion.

EX: A belly flop would be more painful in a small pool of water.

Capillary Action

Capillary action is related to the adhesive properties of liquids.

Liquid molecules are attracted to the straw. As they “climb” up the straw, other molecules follow.

Capillary action is limited by gravity and the size of the straw.

The thinner the straw or tube the higher up capillary action will pull the liquid.

Last slide

Capillary Action

Phase Changes

Phase Changes

Phase changes are due to changes in temperature, which affects kinetic energy; or pressure, which establishes how close the molecules of a substance are.

Melting point- temperature of solid liquidFreezing point (crystallization)- temp of

liquid solidCondensation- gas molecules cool and

condense (come close together) to form a liquid

Sublimation- the direct change from a solid to a gas (dry ice, frozen CO2 CO2 gas)

Vaporization- change from a liquid gasEvaporation- vaporization of liquid gas

below the boiling pointBoiling point- temp at which liquid gas

Some Important Vocab

Heating Curve A graph that represents a substance’s

change from solid to gas.

Boiling point

Melting point

Cooling Curve A graph that represents a substance’s

change from a gas to a solid.

Condensation point

Freezing point

Melting Point

Freezing Point

Vaporization Point

Condensation Point

http://www.kentchemistry.com/links/Matter/HeatingCurve.htm

Phase DiagramsPhase diagrams show how the states of matter in a system are affected by changes in temperature and pressure.

This phase diagram shows the relative temperatures and pressures at which each of the three states of matter can exist.

Note the point labeled triple point. This is the point at which

all three states of matter can exist.

Note the point labeled critical point. This is the point at which,

no matter how much pressure is applied, the substance will exist only in the gas state.

Phase Diagrams

Boiling Point

__________

Freezing Point

__________

Triple Point

__________

Critical Point

__________

Phase Diagram for CO2

Dynamic Equilibrium

Equilibrium

Remember, before a chemical reaction begins, you have only reactants (only N2O4 is present).Once the reaction starts, products are then being made (both N2O4.and NO2 are present)

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N2O4(g) 2NO2(g)

Equilibrium: the extent of a reaction

In stoichiometry we talked about theoretical yields of products, and the many reasons actual yields may be lower.

Another critical reason actual yields may be lower is the reversibility of chemical reactions: some reactions may produce only 70% of the product you may calculate they ought to produce.

MOST REACTIONS DO NOT GO TO COMPLETION AND DO NOT PRODUCE 100% OF THEIR THEORETICAL YEILD

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Equilibrium

In principle, every chemical reaction is reversible ... capable of moving in the forward or backward direction.

Some reactions are easily reversible ...Some not so easy ...

The double arrow implies the reaction is dynamic.

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N2O4(g) 2NO2(g)

Equilibrium is the state in a system in which there is no net change in that system.The rate of the forward reaction is equal to the rate of the reverse reaction.

At that point, the concentrations of all species are constant.

Equilibrium

In a state change system, for example, a beaker of water that is closed off will have two phases.

1. Liquid2. Gas

The point at which there is no increase in the gas particles or no increase in the liquid particles is called equilibrium.

H2O(l) H2 (g) + O2(g)

Equilibrium

When a chemical reaction reaches Equilibrium, it DOES NOT mean that there are the same amount of reactants as there are products.

It just means that the concentrations of the substances remain constant. Ex. H2O(l) H2 (g) + O2(g)

Molecules Evaporating = Molecules Condensing

Equilibrium

A System at Equilibrium

Once equilibrium is achieved, the amount of each reactant and product remains constant.

Chemical Equilibrium Analogy

Let us introduce the idea of chemical equilibrium by an analogy, seemingly far-fetched at first sight, but actually mathematically correct.

Imagine that a crabapple tree sits on the dividing line between two homes, one inhabited by a grouchy old man, and the other by a father who has told his son to go out and rid the back yard of crabapples.

Chemical Equilibrium Analogy

The boy quickly realizes that the easiest way to dispose of the crabapples is to throw them into the neighbouring yard. He does so, arousing the ire of the old man. 

The boy and the man start throwing crabapples back and forth across the fence as fast as they can.

Who will win?Let’s see…

Chemical Equilibrium Analogy Assuming that the

boy is more energetic and agile than the old man, you might think at first that the conflict would end with all of the apples on the old man's side…

Chemical Equilibrium Analogy

It is true that with equal numbers of crabapples on either side, the boy will throw apples across the fence faster than the old man can return them… But this only means that apples will become more plentiful on the old man's side, and easier for him to reach.

Chemical Equilibrium Analogy

The apples will become scarcer on the boy's side, and require more running around to locate. Eventually a standoff, or equilibrium, will be reached, in which the number of apples crossing the fence is the same in both directions.

The old man will throw less quickly but will have less trouble finding apples; the boy will throw more rapidly but will waste time scurrying around hunting for the relatively few crabapples on his side.

The ratio of apples on the two sides of the fence ultimately will be determined by the relative agility of the two combatants, but all of the apples will not end up on one side.

Le Chatelier’s Principle

If stress is applied to a system at equilibrium, the system will tend to readjust so that the stress is reduced and the reaction goes back to equilibrium.

The stress may be a change in temperature, pressure, concentration of products or reactants, or other external factors.

Equilibrium shifts occur after a stress has been applied.

LeChatelier’s Principle

H2O (l) H2O (s)

If we add heat to this system at equilibrium, what will happen?

We call that an equilibrium shift to the left because we will form more of the substance on the left side of the yield sign.

If we place this system in a freezer, what type of equilibrium shift will occur?

LeChatelier’s Principle

Shifts

Shift to the left to make more reactants. Everything on the left increases, everything on the right decreases.

Shift to the right to make more products. Everything on the right increases and reactants decrease.

Stresses to Equilibrium

Only gases and aqueous substances can induce a stress. Addition or elimination of solids or liquids will not affect

equilibrium. They can however, increase or decrease when other stresses occur.

If a stress is added to a system, the system shifts in the direction to relieve the stress.

HINT… Adding a stress – shift to the other side Subtracting a stress – shirt to same side

Changing Concentrations and the Effect on Equilibrium

N2(g) + H2(g) NH3(g)

1. What shift will occur when the [NH3] is increased?

2. What happens to [N2], and [H2]?3. What shift will occur when some H2 is

taken out of the system?4. What happens to [N2], and [NH3]?5. What shift will occur when some NH3 is

taken out of the system?6. What happens to [N2], [H2], and [NH3]?

If temp or energy (J, kJ, cal, kcal) is a reactant then the reaction is endothermic (requires heat) Treat temp as any reactant.

If temp or energy is a product then the reaction is exothermic (releases heat) Treat as any product.

Changing Temperatureand the Effect on Equilibrium

N2(g) + H2(g) NH3(g) + heat

1. What shift will occur when heat is added to the system?

2. What happens to [N2], [H2], and [NH3]?

3. What shift will occur when some NH3 is taken out of the system?

4. What happens to temperature?5. What shift will occur when heat is taken

away from the system?6. What happens to [N2], [H2], and [NH3]?

Changing Temperatureand the Effect on Equilibrium

Applies to gases only. If increasing pressure, shift will occur

in the direction of the least moles. EX: 2 mol 1 mol = right

shift If decreasing pressure, shift will occur

in the direction of the most moles. EX: 2 mol 1 mol = left

shift If moles are equal then there is no

shift and everything remains the same.

Changing Pressureand the Effect on Equilibrium

N2(g) + 3H2(g) 2NH3(g) + heat

1. What shift will occur when pressure is increased?

2. What happens to [N2], [H2], [NH3], and temperature?

3. What shift will occur when pressure is reduced?

4. What happens to [N2], [H2], [NH3], and temperature?

Changing Pressureand the Effect on Equilibrium

K value

The equilibrium constant (K) is a unitless quantity characterizing a chemical equilibrium in a chemical reaction which is a useful tool to determine the concentration of various reactants or products in a system where chemical equilibrium occurs.

It is only affected by temp changes. Use the general equation: K=

[products]

[reactants]

Equilibrium

What Does the Value of K Mean?

• If K >> 1, the reaction is product-favored; product predominates at equilibrium.

• If K << 1, the reaction is reactant-favored; reactant predominates at equilibrium.

Note that during a right shift the concentration of products increases while the concentration of reactants decrease. Mathematically, this increases the K value. (K>>1)

During a left shift the concentration of the reactants increase while the concentration of the products decrease, decreasing the K value. (K<<1)

K value

N2(g) + H2(g) NH3(g) + heat1. What shift will occur when heat is taken

out of the system?2. What happens to the K value?3. What shift will occur when some NH3 is

taken out of the system?4. What happens to the K value?5. What shift will occur when heat is

added to the system?6. What happens to the K value?

Review: EquilibriumConcentration

•only (g) & (aq) cause a shift•(L) and (s) = NO SHIFT

•add… shift to other side

•subtract… shift to same side

Temperature*add… shift to other side*subtract… shift to same side

• ← K << 1• → K >> 1

*K values change only with temperature shifts

*Endothermic – energy on react side (left)*Exothermic – energy on product side (right)

Pressure• ↑Increase P… shift toward lower moles•↓Decrease P… shift toward greater moles•if moles are equal = NO SHIFT

*only gases are affected by pressure

changes