kinetics 1 Flashcards
(30 cards)
What is reaction kinetics?
Reaction kinetics is the study of the rate of chemical reactions and the factors that affect these rates.
Why do we study reaction rates?
To understand how fast a reaction occurs, how to control it, and to determine reaction mechanisms.
What is the rate of a reaction?
The rate of reaction is the change in concentration of reactants or products per unit time, typically expressed in mol dm⁻³ s⁻¹.
How does reaction rate relate to reactant concentration?
Reaction rate is directly related to the concentration of reactants as described by the Rate Law.
What is the Rate Law?
An expression that shows how the reaction rate depends on reactant concentrations: Rate = k[A]ⁿ[B]ᵐ, where k is the rate constant, and n, m are the reaction orders.
Can reaction orders be determined from the balanced equation?
No, reaction orders must be determined experimentally.
What is the rate expression for a reaction A → B?
Rate = -d[A]/dt = d[B]/dt, where d[A] and d[B] are changes in concentration over time.
How do we determine reaction order experimentally?
By using the Method of Initial Rates, where different starting concentrations are used to measure the change in reaction rate.
What happens to the rate when [NO] is doubled in the reaction: 2 NO + O₂ → 2 NO₂?
The rate quadruples if the reaction is second-order with respect to NO.
What is the rate law for the reaction 2 NH₄⁺ + NO₂⁻ → N₂ + 2H₂O?
Rate = k [NH₄⁺][NO₂⁻]
What are the units of the rate constant (k) for first-order kinetics?
s⁻¹ (per second).
What are the units of the rate constant (k) for second-order kinetics?
mol⁻¹ dm³ s⁻¹ or M⁻¹ s⁻¹.
What is the difference between instantaneous and initial reaction rates?
Instantaneous rate is the slope of the concentration-time graph at a given point, while initial rate is the rate measured at the beginning of the reaction.
How can we measure reaction rates?
By monitoring concentration changes over time using techniques like spectrometry, colorimetry, or titration.
What does the reaction rate equation tell us?
How fast reactants are consumed and products are formed in a chemical reaction.
What are zero, first, and second-order reactions?
Zero-order: Rate is independent of reactant concentration.
First-order: Rate depends on the concentration of one reactant.
Second-order: Rate depends on either one reactant squared or two reactants multiplied together.
How do you determine the order of a reaction from a concentration vs. time graph?
Zero-order: [A] vs. time gives a straight line.
First-order: ln[A] vs. time gives a straight line.
Second-order: 1/[A] vs. time gives a straight line.
What is the integrated rate equation for a first-order reaction?
ln[A] = -kt + ln[A₀]
How do you calculate the rate constant (k) for a first-order reaction?
From a ln[A] vs. time graph, the gradient (slope) is -k.
What is the half-life formula for a first-order reaction?
t₁/₂ = 0.693/k
Half-life is constant for first-order reactions.
What are the units of k for different reaction orders?
Zero-order: M/s (mol dm⁻³ s⁻¹)
First-order: s⁻¹
Second-order: M⁻¹ s⁻¹
What is a second-order reaction?
A reaction where the rate depends on either [A]² or [A][B].
How do you determine k for a second-order reaction?
Plot 1/[A] vs. time; the slope of the straight line is k.
What is a pseudo-first-order reaction?
A reaction that is actually second-order but appears first-order because one reactant is in large excess and remains nearly constant.
