Yr13 content Flashcards
(119 cards)
What is the rate of reaction?
The rate of reaction is the change in concentration of a reactant or product per unit time.
Define the term “order” in the context of reaction rates.
The power to which the concentration of a reactant is raised in the rate equation.
What is the rate-determining step in a reaction mechanism?
The rate-determining step is the slowest step in a reaction mechanism that determines the overall rate of the reaction.
What does “overall order” of a reaction mean?
The overall order of a reaction is the sum of the orders with respect to each reactant in the rate equation.
What is the rate constant?
The rate constant (k) is a proportionality constant in the rate equation that is specific to a particular reaction at a given temperature.
Explain the term “half-life” in relation to reaction rates.
The half-life of a reaction is the time taken for the concentration of a reactant to decrease to half its initial value.
How can you deduce the order of a reaction from experimental data?
By analyzing how the rate of reaction changes with varying concentrations of reactants, often using methods such as the initial rates method.
How do you calculate the rate constant, k, from a rate equation?
The rate constant, k, can be calculated by rearranging the rate equation to solve for k: k = rate / ([A]^m[B]^n).
How do you write a rate equation from the orders of reactants in the form: rate = k[A]^m[B]^n, where m and n are 0, 1, or 2?
The rate equation is written by determining the orders (m and n) with respect to each reactant from experimental data and then substituting these values into the general form: rate = k[A]^m[B]^n.
What are the units of the rate constant, k, for different orders of reaction?
“The units of k depend on the overall order of the reaction:
Zero order: mol L⁻¹ s⁻¹
First order: s⁻¹
Second order: L mol⁻¹ s⁻¹”
From a concentration–time graph, how can you deduce the order (0 or 1) with respect to a reactant from the shape of the graph?
For a zero-order reaction, the concentration–time graph is a straight line with a negative slope. For a first-order reaction, the graph is a curve that shows an exponential decrease.
How do you calculate reaction rates from the measurement of gradients on a concentration–time graph?
The reaction rate at any point can be calculated by determining the gradient (slope) of the tangent to the concentration–time graph at that point.
For a first-order reaction, how do you measure the constant half-life, t1/2, from a concentration–time graph?
The half-life for a first-order reaction can be measured as the time interval between successive points where the concentration of the reactant halves.
How do you determine the rate constant, k, for a first-order reaction using the relationship: k = ln 2/t1/2?
The rate constant, k, for a first-order reaction can be calculated using the formula: k = ln 2 / t1/2, where t1/2 is the half-life.
From a rate–concentration graph, how can you deduce the order (0, 1, or 2) with respect to a reactant from the shape of the graph?
“For a zero-order reaction, the rate–concentration graph is a horizontal line.
For a first-order reaction, the graph is a straight line through the origin.
For a second-order reaction, the graph is a curve that increases with the square of the concentration.”
How do you determine the rate constant for a first-order reaction from the gradient of a rate–concentration graph?
The rate constant for a first-order reaction can be determined from the gradient of the rate–concentration graph, as the gradient is equal to the rate constant, k.
How can you predict possible steps in a reaction mechanism from the rate equation and the balanced equation for the overall reaction?
Possible steps in a reaction mechanism can be predicted by comparing the rate equation with the overall balanced equation and identifying intermediates and transition states that are consistent with both.
What techniques and procedures are used to investigate reaction rates by the initial rates method and by continuous monitoring, including the use of colorimetry?
The initial rates method involves measuring the initial rate of reaction for different initial concentrations of reactants. Continuous monitoring involves measuring the concentration of reactants or products at regular intervals throughout the reaction. Colorimetry is used to measure the concentration of colored species by monitoring the absorbance of light.
For a multi-step reaction, how do you predict a rate equation that is consistent with the rate-determining step?
The rate equation for a multi-step reaction can be predicted by identifying the rate-determining step and using the stoichiometry of the reactants involved in that step to write the rate equation.
Provide a qualitative explanation of the effect of temperature change on the rate of a reaction and hence the rate constant.
Increasing the temperature generally increases the rate of a reaction because it increases the kinetic energy of the molecules, leading to more frequent and energetic collisions. This results in a higher rate constant.
What is the Arrhenius equation and how does it describe the exponential relationship between the rate constant, k, and temperature, T?
The Arrhenius equation is k = Ae^(-Ea/RT), where k is the rate constant, A is the pre-exponential factor, Ea is the activation energy, R is the gas constant, and T is the temperature in Kelvin. It shows that the rate constant increases exponentially with an increase in temperature.
How do you determine the activation energy (Ea) and the pre-exponential factor (A) graphically using the equation: ln k = –Ea/RT + ln A derived from the Arrhenius equation?
By plotting ln k against 1/T, a straight line is obtained with a slope of -Ea/R and an intercept of ln A. The activation energy, Ea, can be determined from the slope, and the pre-exponential factor, A, can be determined from the intercept.
What must mole fractions add up to?
one
What must partial pressures add up to?
Total pressure
