Equilibrium Reactions and Le Châtelier's Principle

• CHEM1982 (Winter 2025) is a General Applied Chemistry course
• The current section focuses on Part I Gases; Thermochemistry; Chemical kinetics, and Chemical Equilibrium
• Dr. Mason Lawrence is the instructor

Vapor Pressure and Boiling Point

• The boiling point of a liquid is the temperature where its vapor pressure equals the external pressure
• The normal boiling point of a substance occurs at standard atmospheric pressure, equivalent to 760 torr
• When the external pressure on a liquid rises, the boiling point also goes up

Boiling Point and Intermolecular Forces

• A liquid's boiling point is affected by the strength of its intermolecular forces, because the boiling point relates to vapor pressure, and vapor pressure is affected by the strength of the intermolecular forces
• Weaker intermolecular forces generally mean a lower boiling point

Types of Phase Changes and Their Enthalpies

• Melting, or fusion, occurs when a solid gains kinetic energy as temperature rises, moving particles out of fixed positions
• Freezing is the opposite of melting
• Vaporization occurs when liquid molecules gain sufficient kinetic energy, separating completely to form a gas
• Condensation is the opposite of vaporization
• Sublimation occurs when a solid transitions directly to the gas phase upon increasing temperature
• Deposition is the opposite of sublimation

Heats of Vaporization and Fusion

• The heat of vaporization (ΔH°vap) is always greater than the heat of fusion (ΔH°fus)
• More energy is needed to fully separate molecules compared to just melting

Quantitative Aspects of Phase Changes

• Within a phase, heat flow causes a change in temperature since the average kinetic energy (Ek) of the particles changes such that,
• q = (amount) x (heat capacity) x ΔT
• During a phase change, heat flow occurs at constant temperature, where:
  • q = (amount) x (ΔH of phase change)

Liquid-Gas Equilibrium

• A closed flask system hits dynamic equilibrium, where molecules leave and enter the liquid at the same rate
• Vapor pressure is pressure from the vapor on the liquid
• Pressure grows until equilibrium is achieved
• At equilibrium vapor pressure is constant

Factors Affecting Vapor Pressure

• Vapor pressure is affected by temperature, as well as a substance's type and/or the strength of its intermolecular forces
• As temperature increases, the fraction of molecules with enough energy to enter the vapor phase increases
• As temperature increases, vapor pressure increases, thus higher T implies a higher P
• Weaker intermolecular forces make it easier for particles to enter the vapor phase
• Weaker intermolecular forces cause higher vapor pressure

Quantifying the Effect of Temperature on Vapor Pressure

• The Clausius-Clapeyron equation relates vapor pressure to temperature
• A two-point form of the Clausius-Clapeyron equation is used when vapor pressures at two different temperatures are known
• R = 8.314 J/mol⋅K

Vapor Pressure and Boiling Point

• A liquid's boiling point is where vapor pressure equals external pressure
• Normal boiling point is observed at standard atmospheric pressure (760 torr)
• As external pressure on a increases, its boiling point increases

Boiling Point and Intermolecular Forces

• Boiling point depends on intermolecular forces since vapor pressure is impacted by intermolecular forces
• The weaker the intermolecular forces, the lower the boiling point

Phases of Matter

• A "phase" refers to each physical state of matter that is a physically distinct, homogeneous part of a system
• The properties of each phase are determined by the balance between potential and kinetic energy of the particles
• The potential energy, in the form of attractive forces, tends to draw particles together
• Kinetic energy associated with movement tends to disperse particles

A Comparison of Gases, Liquids, and Solids

• Gases
  • Kinetic energy dominates the potential energy of intermolecular forces
  • On average, gas particles are far apart (low density) and move randomly throughout the container
  • are highly compressible
  • fill its container, taking both the volume and shape of it (high freedom of motion)
  • flow easily through another gas
• Liquids
  • Intermolecular attractions between particles are strong enough to pull the particles closer together
  • touch each other (higher density), move randomly around each other but have limited motion
  • resist an applied force and thus compress only slightly, but less then a solid
  • still have enough kinetic energy to move randomly around each other, so conforms to the shape of its container, but with surface; flows, but less freely compared to gasses
• Solids
  • Intermolecular forces clearly dominate the kinetic energy of the particles; fixed in position (low freedom of motion)
  • Solids exhibit high density; particles jiggle in place; is very difficult to compress
  • Particles have very little motion freedom, so do not take on either the shape nor the volume of its container
  • Solids do not flow significantly

The Molecular Basis of Tension

• A surface molecule experiences a net attraction downward, causing a liquid surface to minimise its surface possible.
• An interior molecule is attracted by others on all sides.
• Surface tension is the required energy to increase the surface area of a liquid; a higher surface tension means stronger forces between particles, the stronger the forces between the particles the higher the surface tension
• An increased temperature translates to a decreased surface temperature

Viscosity

• Viscosity is a fluid's resistance to flow, and derives from intermolecular attractions which cause the molecules to move more slowly around and past each other.
• Stronger intermolecular forces cause higher viscosity
• Increased temperature leads to decreased viscosity
• Molecular shape affects viscosity
• Greater viscosity will be experienced where the molecules have higher viscosities and consist of longer molecules with the same intermolecular forces

Attractive Forces

• Intramolecular (bonding) forces are forces within something.
• Chemical reaction behavior matter is identical, same basic particle exist in each case.
• Intermolecular (non-bonding) forces exert force outside of a molecule.
• Physical matter phase change since strength in forces different from in-between phases

The Nature of Intermolecular Forces

• Intermolecular forces are molecular attractions involving ions/ molecules possessing partial charges
• Intermolecular forces are weak considering bonding forces because particles having smaller charges located apart from from are involved involved

Dipole Moment and Boiling Point

• Molecules with greater dipole moments attract each other more
• Greater dipole moments equate to substances boiling at higher temperatures

Dispersion (London) Forces

• Dispersion/London Force starts w/instantaneous dipole where particle induces dipole & attracts
• Dispersion Force exist in every particle and increases energy for entire matter
• This constitutes only forces of nonpolar particles
• Higher polarizable objects can cause stronger Dispersion Force
• Bigger particles = Stronger force than lower-sized ones
• Dispersion Strength in Force rises along rising Molecular Strength; causing BP to rise

Factors That Affect Equilibrium

• Adding reactants increases will have some result to used up.
• Adding or removing the reaction component will result in equilibrium
• Magnitude never change constant same to the very end

Concentration

• If pressure then added or less reaction will affect reaction, Higher total volume or reduction pressure can benefit side which has gas moles more if it increases the amount but K always remains.

Effect Of temperature

• Reactions which contain heat from within act similar reactants/increase in heat drive reaction K increases, side react
• Exothermic reaction act much as products if increase can push back reactants
• Changes made for concentration pressure doesn’t affect temperature change of the vale K

Reaction Quotient, Q

• Use calculating reactions and directions
• Expression is identical to the expression for K, with same values of concentration
• Current concentration uses initial concentration while equilibrium uses those equilibrium

Le Chatelier's Principle: How a System at Equilibrium Responds to Disturbances

• Le Chatelier's principle states that an change at equilibrium where temperature/pressure component or concentrate the shift by balancing by disturbance.
• System after shift will return equilibrium with concentration where pressure which change value equilibrium which constant K remains the unless same

How A Reaction Affect Equilibrium

• When the amount of either reaction or output change, and if then, how much disturbance adding extra product by balancing disturbance. Extra will have some to used. If its removing, reaction then the component will added if being used usedup Quantity equilibrium constants maintains exact same balance, even changes of a reactions to equilibrum

3)Effect of Catalysts

• Catalysts increase the Rate of forward and backward reactions.
• Activation energy is lower and at temperatures to establish, equilibrum is lowering temperature and the equilibrium is not
• Systems that can equilibrium be catalyzed a catalyst allowing equilibrium to happen

The Concept of Chemical Equilibrium

• Equilibrium is a State of Equal.
• Once reaction on the side is reached with the equilibrum, it is more concentrate.
• Time, has not but reacted and stopped/Dynamic/Chemical Equilibrium proceeds when in reverse rate will the reactions from the same side.

The Equilibrium Constant

• Dynamic reactions for the Chemistry is conditioned or which the rate = reversed reaction.
• Equations come from a double- head arrow:

Equilibrium Constant Expression

• Ratef =Rater & rewriting for it and constant ( k )
• kf (N204]= kr[NO2]^2
• kf/kr =[NO2]^2/[N204]= Kequill This expression or value of K, refers to in what molar is products divided by reactants.

Magnitude For K

• K<<1, The side is in reactions -K about which the reactions about the equal
• K>>1 The output at point has the more side A+BB (k₁)->C or D (k₁) This express the Qty of reactions (Q) = Amounts Of the Product/ Amount of Reactions