Precision Quiz - Chemical kinetics

Temperature Dependence of Rate Constants: Identify the incorrect statement among the following

• According to the Arrhenius equation, a plot of ln(k) versus 1/T (where T is the temperature in Kelvin) yields a straight line with a slope of -Ea/R.

• The Arrhenius equation predicts that the rate constant (k) decreases as the temperature increases, showcasing the temperature's impact on reaction speed.

• Activation energy (Ea) and the gas constant (R) are factors in the Arrhenius equation that determine the temperature dependence of the rate constant.

Molecularity of Reactions: Identify the incorrect statement among the following

• Molecularity refers to the number of reactant particles involved in an elementary step and can only be an integer value.

• The molecularity of a reaction provides direct insight into the reaction mechanism, indicating how reactant molecules come together in the rate-determining step.

• For complex reactions, the overall reaction molecularity is the sum of the molecularities of all the elementary steps in the reaction mechanism.

Rate Law and Rate Constants: Identify the incorrect statement among the following

• The rate law expresses the rate of a chemical reaction as directly proportional to the product of the products' concentrations raised to their respective powers.

• In a rate law equation, the rate constant is a coefficient that combines the effect of temperature and reaction-specific characteristics, remaining constant for a given reaction at a fixed temperature.

• The exponents in the rate law formula represent the orders of the reaction with respect to each reactant, indicating the rate's sensitivity to changes in concentrations.

First-Order Reactions: Identify the incorrect statement among the following

• A first-order reaction's rate law is given by rate = k[A], where [A] is the concentration of the reactant, and k is the rate constant.

• The half-life of a first-order reaction is independent of the initial concentration of the reactants and is a constant for the reaction.

• In first-order kinetics, the time it takes for the reactant concentration to reduce to half its initial value is called the reaction's half-life, which varies with concentration.

Order and Molecularity: Identify the incorrect statement among the following

• The molecularity of a reaction refers to the number of molecules participating in the rate-determining step and is always an integer.

• Reaction order is determined experimentally and can be any fraction, reflecting the reaction rate's dependence on reactant concentration.

• Both reaction order and molecularity describe the same aspect of a chemical reaction, specifically how the reaction rate changes with reactant concentration.

Zero-Order Reactions: Identify the incorrect statement among the following

• In a zero-order reaction, the rate is dependent on the initial concentration of the reactants and varies over time.

• The rate law for a zero-order reaction can be expressed as rate = k, indicating that the reaction rate is directly proportional to the rate constant alone.

• Zero-order kinetics imply that the reaction rate changes with variations in temperature but not with changes in reactant concentrations.

Determining Reaction Order: Identify the incorrect statement among the following

• Reaction order can be determined from the rate law expression, derived from experimental data showing how the reaction rate varies with reactant concentrations.

• The order of a reaction is always equal to the molecularity of the rate-determining step, directly observable from the reaction mechanism.

• A reaction's order is an empirical quantity that must be determined experimentally and cannot be deduced from the stoichiometric coefficients of the reactants alone.

Activation Energy Interpretation: Identify the incorrect statement among the following

• Lower activation energies are associated with slower reaction rates because due to less energy requirement for reactants to transform into products.

• The activation energy of a reaction can be determined graphically using the Arrhenius plot, which relates the rate constant to temperature.

• A reaction's activation energy is a measure of the minimum potential barrier that must be overcome for reactants to form products, impacting the rate significantly.

Activation Energy and the Arrhenius Equation: Identify the incorrect statement among the following

• The Arrhenius equation shows that the rate of a reaction increases exponentially with an increase in temperature due to a decrease in activation energy.

• Activation energy is the minimum energy that reacting molecules must possess for a reaction to occur, as described by the Arrhenius equation.

• The Arrhenius equation illustrates the inverse relationship between activation energy and the rate constant, demonstrating how lower activation energies result in higher reaction rates.

Rate Law for a Second-Order Reaction: Identify the incorrect statement among the following

• For a second-order reaction involving two reactants, the rate law can be written as rate = k[A]^2[B]^2, where k is the rate constant.

• The overall order of a reaction is the sum of the powers of the concentration terms in the rate equation, which equals 2 for a second-order reaction.

• In the rate law expression for a second-order reaction, the exponent on the reactant concentration indicates the reaction proceeds twice as fast with a doubling of the reactant concentration.