Chapter 18 - Rates of reactions Flashcards
What is the equation for rate?
Δconcentration
Rate = ————————-
time
For a reaction A, [A] is shorthand for what?
[A] = concentration of A
What is the unit for rate?
-3 -1
moldm s
Show the relationship between order n and rate.
n
rate ∝ [A]
What is the overall order?
The sum of the individual orders of the reactants.
Give the rate equation for reaction A + B → C with orders m for A and n for B.
rate = k [A]^m[B]^n
What is half-life?
The time taken for any specified property (e.g. concentration) to halve.
What is shown by the gradient of a concentration-time graph?
Rate
How can you calculate the rate constant from rate?
rate
k = ——–
[A]
for reaction A
How can you calculate the rate constant from half-life?
ln 2
k = ————
half-life
What is the rate-determining step?
The slowest step in the reaction mechanism of a multi-step reaction.
The rate equation contains the reactants in the ___________ ______.
Explain why.
The rate equation contains the reactants in the rate-determining step.
The rate determining step is so much slower than the other steps that when you measure the rate of reaction you are measuring the rate of the rate-determining step.
What is the effect of increasing temperature on the rate constant?
The rate constant is proportional to the rate of reaction.
An increasing temperature increases the rate, increasing temperature therefore increases the rate constant.
What is the Arrhenius equation?
-Ea / RT
k = Ae
What is the Arrhenius equation in logarithmic/graphical form?
Ea 1
ln k = - —— —- + ln A
R T
Give 4 examples of rate of reaction experiments.
- Gas evolving experiments
- Mass change
- Colorimetry (colour change)
- pH change
What is a zero order reaction?
rate ∝ [A]^0
Rate is not affected by concentration of reactant A. Constant rate.
What is a first order reaction?
rate ∝ [A]^1
Rate is directly proprtional to the concentration of A.
e. g. if [A] is doubled, rate is doubled
e. g. if [A] is halved, rate is halved
What is a second order reaction?
rate ∝ [A]^2
Rate is proportional to the square of the concentration of A.
e. g. if [A] is doubled, rate is quadrupled
e. g. if [A] is halved, rate is quartered
Concentration-time graphs can be plotted from the results of _______ _________ experiments.
Concentration-time graphs can be plotted from the results of continuous monitoring experiments.
Rate-concentration graphs can be plotted from the results of _____ _____ experiments.
Rate-concentration graphs can be plotted from the results of initial rates experiments.
What is an intermediate?
What is an overall equation?
A species which is formed in one step but used up in another, it is not seen as a reactant or product in the overall equation.
The overall equation is the sum of the species involved in each step.
What is the unit of Ea in the Arrhenius equation?
Jmol-1
Rate-concentration graphs can be plotted from the results of…
…initial rates experiments.
What is a reaction mechanism?
The series of steps that make up a reaction.
