Kinetics
Chemistry - Kinetics
What term describes the overall speed at which a chemical reaction occurs?
rate
Explanation: The reaction rate describes the speed at which reactants are consumed or products are formed over a specific time period.
What substance speeds up a reaction without being permanently consumed?
catalyst
Explanation: A catalyst provides an alternative reaction pathway with a lower activation energy, speeding up the overall reaction without being permanently consumed.
What minimum energy is strictly required to start a chemical reaction?
activation
Explanation: Activation energy is the minimum energetic barrier that colliding reactant molecules must successfully overcome for a chemical reaction to occur.
What increases continuously as the temperature of a reacting system increases?
collisions
Explanation: As temperature rises, molecules move faster, leading to a continuous increase in the frequency and energetic force of molecular collisions.
What state represents the absolute highest energy point along the reaction pathway?
transition
Explanation: The transition state is the brief, highly unstable, maximum-energy configuration of atoms at the absolute peak of the activation energy barrier.
What substance specifically decreases the rate of a chemical reaction when added?
inhibitor
Explanation: An inhibitor is a substance that binds to reactants or catalysts to deliberately slow down or completely halt the rate of a chemical reaction.
What kinetic parameter is solely determined by experiment rather than stoichiometry?
order
Explanation: Reaction order is the experimentally determined exponent of a reactant's concentration in the rate law, which cannot be deduced merely from the balanced equation.
What form of energy is primarily associated with the physical movement of molecules?
kinetic
Explanation: Kinetic energy is the energy of motion, which allows molecules to move rapidly, collide, and provide the necessary force to break chemical bonds.
What specific term refers to a complex biological catalyst found in living cells?
enzyme
Explanation: An enzyme is a highly specific biological protein that acts as a natural catalyst to tremendously accelerate metabolic reactions in living organisms.
What phase describes a catalyst that exists in the same state as the reactants?
homogeneous
Explanation: A homogeneous catalyst exists in the exact same physical phase (such as completely dissolved in a liquid or gas) as the reacting molecules it assists.
What parameter expresses the quantitative speed of reactant consumption over time?
velocity
Explanation: In chemical kinetics, velocity or rate quantitatively describes exactly how fast the concentration of reactants decreases over a measured time frame.
What specific geometric requirement must colliding molecules possess to react successfully?
orientation
Explanation: Reacting molecules must collide with the correct spatial alignment, or orientation, to ensure their reactive electron clouds can interact effectively.
What physical action happens to the reaction rate when reactant concentration increases?
increases
Explanation: Higher reactant concentration packs more particles into the same volume, which dynamically increases the frequency of effective collisions and speeds up the reaction.
What factor involves breaking a solid reactant into smaller pieces to speed up a process?
area
Explanation: Increasing the surface area by breaking a solid reactant into smaller pieces exposes more particles to collisions, thereby speeding up the overall process.
What type of reaction energetically releases heat to its surrounding environment?
exothermic
Explanation: Exothermic reactions release more energy when forming product bonds than they consume when breaking reactant bonds, releasing net heat to the environment.
What mathematical expression formally relates the reaction rate to reactant concentrations?
law
Explanation: The rate law is a mathematical equation derived from empirical experiments that connects the reaction speed directly to the specific concentrations of reactants.
What fixed proportionality value links the kinetic rate to the concentration variables?
constant
Explanation: The rate constant (k) is a proportionality factor specific to a reaction at a given temperature, perfectly linking the kinetic rate to concentration variables.
What represents the discrete number of molecules participating in an elementary step?
molecularity
Explanation: Molecularity defines the precise number of individual reactant particles (atoms, molecules, or ions) colliding and reacting in a single elementary step.
Which individual step strictly limits the overall speed in a multi-step mechanism?
determining
Explanation: The rate-determining step is the slowest single step in a complex multi-step mechanism, acting as a bottleneck that directly dictates the overall reaction speed.
What chemical species is formed in one step of a mechanism and consumed in another?
intermediate
Explanation: An intermediate is a temporary, highly reactive species generated in an early step of a mechanism and completely consumed in a subsequent step.
What happens physically to the reaction rate when the activation energy barrier is lowered?
accelerates
Explanation: Lowering the activation energy allows a much larger statistical fraction of molecules to successfully react, which physically accelerates the reaction rate.
What analytical device can measure color intensity changes to determine reaction rates?
spectrometer
Explanation: A spectrometer precisely measures changes in light absorption or color intensity over time, allowing chemists to continuously track the progress of a reaction.
What physical property is often measured over time to track the rate of gas production?
pressure
Explanation: For chemical reactions involving gases, tracking dynamic changes in the internal system pressure over time is a reliable way to measure the reaction rate.
What standard SI unit typically expresses time in classical kinetic rate measurements?
seconds
Explanation: The standard SI unit of time used in classical kinetic rate expressions and measurements is the second, commonly appearing in rate constant units.
What standard unit formally measures the concentration of a chemical substance in solution?
molarity
Explanation: Molarity (measured in moles per liter) is the standard and most common unit for expressing the concentration of a chemical substance in a solution.
What descriptive term classifies a collision that successfully results in product formation?
effective
Explanation: An effective collision is one where reacting particles collide with sufficient activation energy and the correct geometric orientation to successfully form products.
What happens dynamically to the average kinetic energy of gaseous particles when cooled?
decreases
Explanation: Cooling a gas dynamically decreases the particles' average kinetic energy, meaning they move much slower and collide significantly less forcefully.
What geometric feature on a concentration-time graph yields the instantaneous reaction rate?
slope
Explanation: The geometric slope of the tangent line on a concentration-versus-time graph directly yields the exact instantaneous reaction rate at that specific point.
What term characterizes a chemical reaction that continuously absorbs heat from its surroundings?
endothermic
Explanation: Endothermic reactions require a continuous input of thermal energy from the surroundings to overcome the energy required to break reactant bonds.
What famous equation mathematically relates the kinetic rate constant directly to temperature?
Arrhenius
Explanation: The Arrhenius equation is a famous physical chemistry formula that mathematically relates the kinetic rate constant of a reaction directly to the absolute temperature.
What kinetic reaction order has a totally constant rate independent of reactant concentration?
zero
Explanation: In a zero-order reaction, the overall rate is a constant value and does not change regardless of increases or decreases in the reactant concentration.
What specific reaction order features a half-life that is perfectly independent of initial concentration?
first
Explanation: A first-order reaction has a uniquely constant half-life, meaning it takes the exact same amount of time to halve the concentration regardless of the starting amount.
What parameter equals the sum of the respective exponents in the experimental rate law?
overall
Explanation: The overall reaction order is easily found by adding together all the individual fractional or integer exponents of the reactant concentrations in the rate law.
What specific integer exponent corresponds to a rate law where doubling concentration doubles the speed?
one
Explanation: For a first-order reactant (an exponent of one), doubling its molecular concentration directly and perfectly doubles the speed of the chemical reaction.
What kinetic term describes a simple elementary reaction involving exactly one single reactant molecule?
unimolecular
Explanation: A unimolecular elementary reaction involves the spontaneous physical decomposition or structural rearrangement of one single, isolated reactant molecule.
What is the fundamental molecularity of an elementary step involving two distinct colliding molecules?
bimolecular
Explanation: A bimolecular step is characterized by the simultaneous physical collision and chemical interaction of exactly two distinct molecules to create products.
What specific Arrhenius factor formally represents both atomic collision frequency and correct geometric orientation?
preexponential
Explanation: The preexponential factor (A) in the Arrhenius equation mathematically accounts for both the total collision frequency and the probability of correct steric orientation.
What modern theory assumes colliding reactants form a high-energy complex before becoming products?
transition
Explanation: Transition state theory postulates that reacting molecules form a highly energetic, unstable activated complex at the reaction's peak before relaxing into stable products.
What fluid property strictly limits the maximum possible rate in a diffusion-controlled liquid reaction?
viscosity
Explanation: In diffusion-controlled liquid reactions, the solvent's physical viscosity strongly dictates how quickly molecules can move through the fluid to physically encounter each other.
What kinetic order is explicitly implied if a plot of the natural logarithm of concentration versus time is strictly linear?
first
Explanation: If plotting the natural logarithm (ln) of a reactant's concentration against time produces a perfectly straight line, it mathematically proves first-order kinetics.
What specific reaction order is reliably indicated if a plot of inverse concentration versus time is perfectly linear?
second
Explanation: A perfectly straight line on a graph of inverse concentration (1/[A]) plotted against time reliably indicates that the reaction kinetics are definitively second-order.
What descriptive term characterizes a reaction mechanism consisting of single irreducible steps?
elementary
Explanation: An elementary reaction represents a single, indivisible molecular event or irreducible step that makes up a broader, more complex overall reaction mechanism.
What kinetic approximation assumes the concentration of a reactive intermediate remains roughly constant?
steady
Explanation: The steady-state approximation assumes that highly reactive chemical intermediates are consumed almost as quickly as they are formed, keeping their concentration stable.
What subtle kinetic effect occurs specifically when a heavier element isotope logically replaces a lighter one?
isotope
Explanation: The kinetic isotope effect occurs when substituting a heavier isotope (like deuterium for hydrogen) measurably slows down the reaction rate due to stronger covalent bonds.
What physical metric conceptually measures the randomness affecting the kinetic pre-exponential factor?
entropy
Explanation: The entropy of activation conceptually measures the strict degree of physical disorder or randomness required for molecules to perfectly align into the correct transition state.
What specific type of catalysis involves reacting substances and the catalyst existing in completely different physical phases?
heterogeneous
Explanation: Heterogeneous catalysis happens when the catalyst exists in a distinct physical phase (such as a solid metal lattice) compared to the reactants (such as free gases).
What unique type of reaction naturally speeds itself up because it continuously produces its own catalyst?
autocatalytic
Explanation: In an autocatalytic reaction, one of the final reaction products inherently serves as a catalyst, meaning the reaction naturally accelerates as it proceeds.
What complex type of reaction mechanism directly involves continuous repeating cycles of propagation steps?
chain
Explanation: Chain reactions feature highly complex, self-sustaining cycles of propagation steps where a reactive intermediate creates products while regenerating another intermediate.
What thermodynamic state strictly occurs when forward and reverse chemical reaction rates become absolutely equal?
equilibrium
Explanation: Dynamic chemical equilibrium is formally reached when the opposing forward and reverse reaction rates match exactly, keeping overall measurable concentrations absolutely constant.
What fundamental integer order corresponds to a kinetic rate constant with standard units of inverse molarity inverse seconds?
two
Explanation: A second-order (two) rate constant typically carries standard units of inverse molarity inverse seconds (M⁻¹s⁻¹) to properly balance the kinetic rate equation.
What precise term perfectly describes a reaction rate measured exactly at the exact moment time begins?
initial
Explanation: The initial rate is the instantaneous speed of the chemical reaction measured exactly at time zero, before any measurable products have formed.
What specific term effectively describes the calculated reaction rate at any specific arbitrary moment in time?
instantaneous
Explanation: The instantaneous rate calculates the exact kinetic speed of the reaction at one specific arbitrary moment, mathematically derived from the derivative of the curve.
What mathematical function deeply relates the kinetic rate constant directly to the exponential activation energy?
exponential
Explanation: The Arrhenius equation proves that the rate constant has a fundamental exponential mathematical dependence on both the absolute temperature and the activation energy barrier.
What environmental variable strictly determines the statistical fraction of molecules possessing enough kinetic energy to react?
temperature
Explanation: Temperature directly dictates the kinetic energy distribution of the system, determining exactly what statistical fraction of molecules crosses the required activation energy threshold.
What classical thermodynamic term formally represents the total heat of reaction but dictates nothing about its kinetic speed?
enthalpy
Explanation: Enthalpy of reaction describes the overall heat change between products and reactants but has absolutely no bearing on the kinetic activation barrier or reaction speed.
What theoretical outcome happens to the kinetic rate constant as the required activation energy theoretically approaches zero?
maximizes
Explanation: As activation energy theoretically drops to zero, every single collision possesses enough energy to react, which maximizes the rate constant to its absolute upper limit.
What fundamental scientific discipline is explicitly defined as the study of chemical reaction rates and their microscopic mechanisms?
kinetics
Explanation: Chemical kinetics is the precise scientific discipline dedicated to the study of reaction speeds, the environmental factors affecting those speeds, and the step-by-step mechanisms involved.
What highly reactive chemical intermediate is typically characterized by an atom possessing one unpaired valence electron?
radical
Explanation: A radical (or free radical) is a highly unstable and reactive chemical intermediate featuring an atom with an unpaired valence electron, driving complex chain mechanisms.
What specific biochemical term accurately describes the temporary or permanent blocking of a biological enzyme's active site?
inhibition
Explanation: Enzyme inhibition occurs when a molecule physically blocks the enzyme's active site or alters its overall shape, completely preventing the true substrate from properly reacting.
What term defines a reaction step requiring three molecules to collide simultaneously with correct energy and orientation?
termolecular
Explanation: A termolecular step requires the incredibly rare and statistically unlikely simultaneous physical collision of exactly three distinct particles with the correct energy and geometry.
