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.
Physical Sciences>Chemistry>Inorganic>Chemical Reaction>Rate
5-Chemistry-Inorganic-Chemical Reaction-Rate
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Date Modified: 2022.0224