Substances have chemical reactivity {activity, chemical} {chemical activity}| {chemical potential, reactivity}. Chemical activity expresses true concentration or pressure. Substance concentration relative to other concentrations depends on chemical potential. Solids and pure liquids, including water, have chemical activity one. Metal activities, in decreasing order, are Li, K, Ba, Sr, Ca, Na, Mg, Al, Mn, Zn, Cr, Fe, Cd, Co, Ni, Sn, Pb, H, Cu, Ag, Pd, Hg, Pt, and Au. Non-metal activities, in decreasing order, are F, Cl, Br, and I.
Chemical potential difference {affinity, reaction}| from reactants to products is chemical-reaction driving force.
Substance partial pressure {fugacity}|, relative to other partial pressures, depends on chemical potential.
Methods can control reaction {reaction control}. In non-polar solution, if activation energy is low, diffusion controls reaction. In ionic solutions, if activation energy is high and is late in reaction, use vibration at frequency similar to rotation frequencies to control reaction, because bonds are short. In ionic solutions, if activation energy is high and is early in reaction, use translational energy to control reaction, because bonds are long.
Lasers can initiate photolytic reactions {flash photolysis}.
Mixing chambers and controlled reactant flows control reaction {flow technique}.
Molecule streams {molecular beam} can hit other molecules at precise speeds and orientations.
Temperature can change equilibrium {relaxation method, chemistry}, if reaction requires heat.
Reaching chemical-reaction transition state requires energy {activation energy}| (Ea). Transition state has potential energy that is higher than reactant potential energy and is higher than product potential energy. For drugs, activation energy equals site-atom attached-hydrogen effective activation-energy sum.
Chemicals {catalyst}| can increase reaction rate, but chemical reaction does not alter them.
amount
Reaction needs only small catalyst amount, because reaction reuses catalyst. However, catalysts can break down, have dirt or product coatings, or have surface damage.
processes
Catalysts reduce energy needed to start reaction. Catalysts allow transition state with lower activation energy, make molecule easier to attack, allow leaving group to leave easier, make attacking group attack better, orient molecules for optimum bond stretching, provide functional groups for forces or transfer, or line up reactant molecules.
types
Enzymes are protein catalysts.
Acids and bases are catalysts {homogeneous catalyst}. Basic catalysts cause isomerization, halogenation, or condensation. Acid catalysts cause tautomerism, solvolysis, or inversion. Neutral catalysts polarize solvent.
types: solid
Solid catalysts {heterogeneous catalyst} provide structured surfaces. Ceramic or metal catalysts are for industrial processes. Surface chemistry is for catalysis, corrosion, membranes, surface tension, and electrodes.
If molecule collision energy with surface is same as surface thermal-vibration energy, surface can absorb molecule and collision energy. Molecule-absorption rate depends on collision energy. Electrode surfaces have an ion layer, covered by an opposite-charge ion layer.
Catalytic surfaces must not bind too strongly or too weakly. Collision rate is not important, because absorption surface is large. Activation energy is small and not determining factor for surface catalysts.
As atoms bind to catalyst, catalyst surfaces orient molecules and dissociate molecular bonds. Then new bond can form by collision or reorientation. Molecules on catalysts can move depending on impurities, defects, and crystal planes. Movement allows reaction atom transfer.
types: gas and metals
Gas molecules chemisorb on metals, because metal absorption area is much greater than gas collision area, so entropy decreases. How saturated surface is affects absorption. If concentration is high or time on surface is long, absorption is less. Because neighboring sites move, they affect absorption sites.
Metals bind oxygen strongest, then acetylene, ethylene, carbon monoxide, hydrogen, carbon dioxide, and nitrogen. Platinum, iron, vanadium, and chromium can adsorb all these substances. Manganese and copper can adsorb some. Magnesium and lithium only absorb oxygen. Iron, nickel, platinum, and silver surfaces are catalysts for hydrogenations and dehydrogenations.
Nickel oxide, zinc oxide, and magnesium oxide are catalysts for oxidations and dehydrogenations, because they are semiconducting. Metal sulfides are catalysts for desulfurations, because they are semiconducting. Aluminum oxide, silicon oxide, and magnesium oxide are catalysts for dehydrations, because they are insulators. Phosphoric acid and sulfuric acid are catalysts for polymerizations, isomerizations, alkylations, and dealkylations {cracking, petroleum}.
Chemical reaction starts when outside energy stretches, twists, or compresses molecule chemical bonds {initiation, reaction}.
energy
Energy typically comes from heat or light. Light adds electric energy and affects electrons directly. Heat makes molecules move faster with more kinetic energy, causing more and higher-energy molecule collisions.
size
In large molecules, collision is less likely to disrupt bond, because collision is more likely to hit other bonds.
shape
Molecule shape determines if collision affects bond. If collision is along bond line, bond disruption is more than if collision is from side.
charge
Bond disruption is greater if colliding atoms have opposite electric charges. Bond disruption is greater if colliding atoms have same electric-charge absolute value.
Light can cause chemical reaction {photoactivation}, as in photosynthesis.
Chemical bond is stable state with relatively low potential energy. See Figure 1. Collision, heat, or radiation can stretch, twist, or compress chemical bond to maximum extent {transition state}| {activated complex}, as molecule electrical attractions resist chemical-bond disruption. Transition state has greatest disruption, highest potential energy, and maximum separation. See Figure 2. If it can become new conformation or molecule, transition state is hybrid of stable chemical states before and after chemical reaction.
From transition state, molecules can go back to original states or become new conformations or molecules, with equal probability. See Figure 3.
After displacement from equilibrium, system returns to equilibrium and sum of all work done by forces during displacement and return equals zero {principle of virtual work} {virtual work principle}.
Chemical-reaction equation {chemical equation} uses molecule chemical formulas and special symbols. Reactant formulas are on left, and product formulas are on right.
direction
Horizontal arrow pointing right separates reactants from products. Delta symbol means to add heat. hv symbol means to add light.
terms
Plus signs separate molecules.
symbols
Up arrow (^) at formula right indicates that reaction produces gas. Down arrow at formula right indicates that reaction precipitates solid. The letter s at formula right means that reagent is solid. The letter l at formula right means that reagent is liquid. The letter g at formula right means that reagent is gas. The letters aq at formula right mean that reagent is aqueous.
balance
Atoms on chemical-reaction left must also be on right, so both sides have same atom numbers and types {conservation of mass, chemical equation}.
Before chemical reaction, chemicals {reactant}| {reagent} exist.
If chemical reaction has more than one reactant, one reactant {limiting reagent}| depletes first as reaction proceeds. Find limiting reagent from balanced chemical reaction, using the following rule. If first-reactant coefficient to second-reactant coefficient ratio is larger than first-reactant moles to second-reactant moles ratio, second reactant is limiting reagent.
After chemical reaction, new chemicals {product, reaction}| exist.
Relative reactant and product masses have relations {stoichiometry}|.
If written chemical reaction has one product or reactant missing, calculations {balancing chemical equation} can find missing product or reactant. If written chemical reaction has one coefficient missing, calculations can find missing coefficient.
First, find all missing atoms, because each atom on left must also be on right.
Using found atoms, write positively charged atom symbol first and negatively charged atom symbol second.
Use naming-formula rules to find candidate molecule, using number subscripts for symbols if necessary.
Write equation using candidate molecule.
Add coefficients to reactants and products to make atom numbers equal on both sides. To find coefficients, first balance metal-atom coefficients, then balance non-metal-atom coefficients, except H and O, then balance hydrogen coefficients, and finally balance oxygen coefficients. If chemical equation is not yet balanced, double metal-atom coefficients, then balance non-metal-atom coefficients, except H and O, then balance hydrogen coefficients, and finally balance oxygen coefficients.
In chemical reactions, total mass {conservation of mass, reaction}, total charge {conservation of charge}, and total energy {conservation of energy, reaction} stay constant. Sum of reactant charges equals sum of product charges. Total reactant mass equals total product mass. Reactant energy equals product energy plus heat.
In chemical reactions, formed or used gas volumes relate by whole-number ratios {combining volumes law} {law of combining volumes} {Guy-Lussac law} {law of Guy-Lussac}.
In reaction series, in which previous-reaction products are next-reaction reactants, total change over series equals sum of reaction changes {Hess' law} {Hess law}.
Chemical-reaction product amount {yield, reaction}| never equals maximum theoretical product amount, because reactions are inefficient. Calculating reaction efficiency {percent yield} uses the balanced chemical reaction. Percent yield equals ratio between product moles and limiting-reagent moles, expressed as percentage.
Knowing chemical equation and reactant and product concentrations at equilibrium allows reaction-constant calculation {equilibrium constant}|. Equilibrium constant is product of product concentrations, each raised to power of its chemical-equation coefficient, divided by product of reactant concentrations, each raised to power of its chemical-equation coefficient. For example, in chemical equation 2 A + 3 B -> C + 4 D, equilibrium constant K = ([A]^2 * [B]^3) / ([C] * [D]^4). Chemical reaction aX + bY -> cZ + dW equilibrium constant is K = (X^a * Y^b) / (Z^c * W^d).
tables
People know many reaction equilibrium constants, at specific temperatures. Dissociating acids and bases have equilibrium dissociation constants. Dissolving salt in water or other solvent has equilibrium solubility constant.
irreversible
Equilibrium constant greater than 10^9 means reaction is irreversible.
product concentrations
Equilibrium constant and initial reactant concentrations result in product concentration at equilibrium. First, use chemical equation to make equilibrium-constant equation with correct exponents. In equilibrium-constant equation, replace product concentration with x if coefficient is 1, replace with 2*x if coefficient is 2, replace with 3*x if coefficient is 3, and so on. If coefficient is 1, replace reactant concentration with its initial concentration minus x. Replace with 2 * (initial concentration minus x) if coefficient is 2. Replace with 3 * (initial concentration minus x) if coefficient is 3, and so on. For example, for chemical equation 2 A + 3 B -> C + 4 D, equilibrium constant K = ([A]^2 * [B]^3) / ([C] * [D]^4). To find A concentration: K = ((2*x)^2 * B^3) / (C * D^4). Use equilibrium constant value from table of constants. Solve for x.
Product concentration is x times its coefficient in chemical equation. Reactant concentration is (initial concentration minus x) times its coefficient in chemical equation.
partition functions
Reactant and product partition functions can find chemical-reaction equilibrium constant.
After reaction, reactant and product amounts stay constant {equilibrium, reaction}|. At equilibrium, total-energy change is zero, free-energy change is zero, substance change is zero, all chemical potentials are equal, and all forces are equal. Product concentrations and reactant concentrations have equilibrium-constant ratio.
rates
At equilibrium, forward and backward reaction rates are equal. Product-formation rate equals reactant-formation rate. Amounts do not change, so reaction is complete.
factors
Equilibrium concentrations and amounts do not depend on catalyst or factors affecting reaction rate. Equilibrium concentrations depend only on energies and entropies.
factors: temperature
If reaction requires heat, temperature increase makes more product.
factors: pressure
If gas is reactant, pressure increase makes more product. If temperature increases, system acts to reduce pressure and so return to equilibrium.
factors: amount
Adding more reactants changes them to products, until equilibrium reestablishes. Adding more products turns them into reactants, until equilibrium reestablishes. Increasing reactant concentration, or removing product, increases product.
Reactions have different forms {reaction types}: chain, synthesis, decomposition, substitution, metathesis, nucleophilic, electrophilic, and molecular rearrangement.
Phosphoric acid and sulfuric acid are catalysts for carbon-chain dealkylations {cracking, dealkylation}| {dealkylation}. Petroleum separation uses phosphoric acid, sulfuric acid, silicon oxide, and aluminum oxide. Silicon oxide and aluminum oxide build branched hydrocarbons. Olefins form on platinum with silicon oxide, followed by isomerization, ring formation, splitting, and hydrogenation.
Two chemicals can bind to make something with different properties than original chemicals {hypergolic}. For example, hydrazine and nitrogen tetroxide react when in contact to make nitrous oxide and water: N2H2 + NO4 -> 3 NO + H2O [where 2 and 4 are subscripts].
Pressure can cause luminescence {triboluminescence}.
Product can be reactant, which can make more product {chain reaction, chemistry}|. Reaction rate continually increases, until system physically disrupts.
One reactant can make two products {decomposition reaction}. Decomposition includes hydrolysis and dehydration reactions.
Chemical can attack negatively charged group {electrophilic reaction}.
Two compounds can make two new compounds {double replacement reaction} {metathesis reaction}. Acid-base reactions have metathesis. Metal compounds can catalyze carbon-carbon double-bond changes.
One reactant can change to same chemical in different configuration {molecular rearrangement}.
Chemical can attack positively charged group {nucleophilic reaction}.
Element and compound can make another element and another compound {single replacement reaction} {substitution reaction, inorganic}. Metal-atom to metal-ion oxidation has substitution.
Two reactants can make one product {synthesis reaction}. Synthesis includes polymerization, hydration, and oxidation reactions, like rusting and combustion.
Energy transfer can involve permanent change that cannot reverse {irreversible reaction}, because heat is made.
Energy transfer can have no friction or other opposing changes {reversible reaction}. In reversible reactions, external and internal temperatures and pressures are approximately the same. In reversible processes, system and surroundings are always in equilibrium. Reversible processes approximate slow energy transfer with small force and minimal resistance.
In reactions {spontaneous reaction}, activation energy can be less than difference in potential energy between transition state and products.
Chemical reactions can release or absorb thermal energy {heat of reaction}|.
Chemical reactions {endothermic reaction} absorb energy if product potential energy is higher than reactant potential energy. Endothermic reactions make complex molecules and require high temperature or strong light at specific frequency.
Chemical reactions {exothermic reaction} release energy {heat, reaction} if reactant potential energy is higher than product potential energy.
Reactions {monomolecular reaction} can have one reactant, as in SN1 and E1 reactions. Molecule vibrations and rotations can cause molecule to decay to new state, as in gas decays, Type I nucleophilic substitutions, Type I eliminations, dissolution, and state changes.
Reactions {bimolecular reaction} can have two reactants, as in SN2 and E2 reactions. Molecule collisions can form transition states and can transfer energy or functional groups, as in isomerizations, Type II nucleophilic substitutions, Type II eliminations, enzyme reactions, syntheses, and dimerizations.
Reactions {termolecular reaction} can have three reactants, as in enzymatic reactions.
Chemical reactions proceed over time {reaction rate}|.
rate
Reaction goes in two directions at once, from reactants to products {forward reaction} and products to reactants {reverse reaction}. Backward reaction rate divides into forward reaction rate to find overall rate.
half-life
Reactant amount eventually reaches half original amount {half-life, reactant}: half-life = C * (1 / c^(n - 1)), where C is constant, c is concentration, and n is reaction order.
factors
Reaction rate depends on temperature, pressure, reactant concentrations, catalysts, states, and reactant physical forms: rate constant = (collision frequency) * e^(-E / (R*T)), where R is gas constant, T is temperature, and E is activation energy. If reactant concentration is in excess, concentration stays constant during reaction.
process
Reactants and products have initial, intermediate, and final concentrations. Reactions destroy reactants and makes products.
process: mechanism
Reaction rate depends on reaction mechanism. Reaction mechanism can depend on zeroth, first, second, or third reactant-concentration power {order, reaction}.
Reaction rate can be constant {zero-order reaction}.
Reaction rate can depend on one reactant concentration or pressure {first-order reaction}. First-order reaction uses linear equation: rate = dC / dt = k * C0 where dC is concentration change, dt is time change, k is rate constant, and C0 is concentration. ln(C / C0) = -k*t, where C is concentration, C0 is initial concentration, k is rate constant, and t is time. Find final and intermediate product or reactant concentrations from initial concentration, rate constant, and time: Cf = Ci * e^(k*t), where Cf is final concentration, Ci is initial concentration, k is rate constant, and t is time.
Reaction rate can depend on two reactant concentrations or pressures {second-order reaction}. Second-order reaction uses quadratic equation.
process: temperature
Reaction rate depends directly on temperature. Reaction rate is faster with higher temperature. 10-K increase doubles reaction rate.
process: form
Reactant physical form affects reaction rate. Greater surface area, lower viscosity, and higher solvent polarity increase reaction rate. If surfaces must touch for reaction, rate depends on contact area.
process: state
Reactant gas, liquid, or solid physical state affects reaction rate.
process: rate constant
Physical factors that affect reaction rate are temperature, catalyst, physical form, and physical state. All physical factors are in one constant {rate constant}. People know rate constants for many chemical reactions.
process: rate-limiting
In chemical-reaction series, in which previous-reaction products are next-reaction reactants, one reaction {rate-limiting reaction} is slowest.
process: ions
Ionic reactions are fast if both reactants have opposite charge. Large ions and high-charge ions increase reaction rate. Increased ionic strength increases rate, if ions have opposite charge, but otherwise slows reaction rate. Solvents with high dielectric constants, like water, reduce repulsions and attractions between reactants and slow reaction rates.
Acid-base reactions are ionic, and reaction rate increases with more acid or base. Ions can modify reaction by forming weak acids and bases.
In ionic solutions, higher ionic strength, more polar solvent, and greater ion charge causes high collision rate and short contact time, so reaction rate is higher.
process: non-polar
In non-polar solutions, higher viscosity makes contact longer and collision rate lower, so reaction rate is lower.
5-Chemistry-Inorganic-Chemical Reaction
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Date Modified: 2022.0225