5A - The rate equation Flashcards
define Order of a reaction
The power to which the concentration of a reactant is raised in the rate equation
define Overall Order of a reaction
The sum of the individual orders of the reactants in the rate equation, m+n
define Rate constant, k
The constant that links the rate of reaction with the concentrations of the reactants raised to the powers of their orders in the rate equation
define Half-life
The time taken for the concentration of a reactant to decrease by half
define Rate-determining step
The slowest step in the reaction mechanism of a multi-step reaction
Write out the formula from the rate equation
Rate = k [A]^m [B]^n
Which reactants appear in the rate equation?
The reactants that are present in the rate-determining step
What happens to the rate of reaction when you double the concentration of a reactant that is: a. Zero Order b. First Order c. Second Order
The rate will: a. Stay the same b. Double c. Quadruple
Rearrange the rate equation to give k
k = rate / [A]m [B]n
Sketch the shape of a concentration-time graph for: a. A Zero Order reaction b. A First Order reaction c. A second order reaction
Graphs:
Which concentration-time graph has a a decreasing, constant, and increasing half-life?
decreasing: zero constant: first increasing: second
Give the equation used to find k from the graph with the constant half-life.
k = ln 2 / t1/2
How would you find k from a Zero Order concentration-time graph?
Calculate the gradient
How would you find k on a Zero Order and on a First Order rateconcentration graph?
Zero Order = y-intercept First Order = gradient
What graph could you draw for a Second Order reaction that would allow you to calculate k directly from the graph?
Plot a graph of rate – concentration squared (rate- [X]^2 ) and then calculate the gradient
How could you propose a plausible reaction mechanism?
(1) Use the rate equation to find the species in the Rate Determining Step (2) Suggest a series of steps with no more than TWO colliding particles
How does an increase in temperature affect the rate constant?
As the temperature increases, so does the rate constant
Why does the rate of reaction increase as the temperature is increased?
The proportion of molecules with an energy greater than or equal to the activation energy (E ≥ Ea) increases and the kinetic energy of the particles increases, causing more frequent collisions.
Write out the ln form of the Arrhenius Equation in the form y= mx+c
Ln k = -Ea/R x 1/T + ln A y = ln k m = -Ea/R x = 1/T c = ln A
. Sketch the shape of a rate-concentration graph for: a. A Zero Order reaction b. A First Order reaction c. A Second Order reaction
