5.1.1
How Fast?
Section 5.1.1 covers rate, order, overall order, the rate constant, half-life and the rate-determining step; deducing orders and rate equations from experimental data; calculating k and its units; concentration–time graphs including the constant half-life of a first-order reaction and k = (ln 2) / (t½); rate–concentration graphs; the initial-rates and continuous monitoring techniques including colorimetry; predicting mechanisms from rate equations; and the Arrhenius equation with the graphical determination of Eₐ and A. PAG 10 supplies the rate data.
Revision Notes
7 revision notes, in the order the specification teaches them.
Rate Equations, Orders and the Rate Constant
Rate equations: orders of reaction, the rate constant k, overall order and working out the units of k.
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Techniques for Measuring Rates
Measuring rates: titration, colorimetry, mass and gas-volume methods, continuous monitoring and the initial-rates method with clock reactions.
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Concentration–Time Graphs and Half-Life
Concentration–time graphs: deducing order from the shape, tangents and rates, half-life and first-order reactions, k from the half-life.
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Rate–Concentration Graphs and the Initial-Rates Method
The initial-rates method: rate–concentration graphs, deducing orders from tables of data, writing the rate equation and calculating k.
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The Iodine–Propanone Reaction
The iodine–propanone reaction: collecting rate data, the orders with respect to iodine, propanone and H⁺, and deducing the mechanism.
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Rate-Determining Step and Reaction Mechanisms
The rate-determining step: rate equations from mechanisms, mechanisms from rate equations, intermediates, and Sₙ1/Sₙ2 evidence from haloalkanes hydrolysis.
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Activation Energy and the Arrhenius Equation
The Arrhenius equation: temperature and the rate constant, ln k against 1/T graphs and finding the activation energy from the gradient.
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Orders and Rate Equations Map
OCR A Level Chemistry A (H432) · 5.1.1 How fast? · Orders and rate equations
The whole section on one A4 page: measuring a rate, rate equations, units of k, initial rates, graph shapes and half-life, with worked examples.
Mechanisms and Temperature Map
OCR A Level Chemistry A (H432) · 5.1.1 How fast? · Mechanisms and temperature
The whole section on one A4 page: the slow step, mechanisms from rate equations, activation energy and temperature, the Arrhenius equation and plot, and the activation-energy practical.
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5.1.1
- b (ii)
deduction of a rate equation from orders of the form: rate = k[A]m[B]n, where m and n are 0, 1 or 2
Revise - d (i)
from a concentration–time graph: deduction of the order (0 or 1) with respect to a reactant from the shape of the graph
Revise - d (ii)
from a concentration–time graph: calculation of reaction rates from the measurement of gradients (see also 3.2.2 b)
Revise - e
from a concentration–time graph of a first order reaction, measurement of constant half-life, t1/2
Revise - f
for a first order reaction, determination of the rate constant, k, from the constant half-life, t1/2, using the relationship: k = ln 2/t1/2
Revise - g (i)
from a rate–concentration graph: deduction of the order (0, 1 or 2) with respect to a reactant from the shape of the graph
Revise - g (ii)
from a rate–concentration graph: determination of rate constant for a first order reaction from the gradient
Revise - h i
the techniques and procedures used to investigate reaction rates by the initial rates method (see also 3.2.2 e)
Revise - h ii
the techniques and procedures used to investigate reaction rates by continuous monitoring, including use of colorimetry (see also 3.2.2 e)
Revise - i (i)
for a multi-step reaction, prediction of a rate equation that is consistent with the rate-determining step
Revise - i (ii)
for a multi-step reaction, prediction of possible steps in a reaction mechanism from the rate equation and the balanced equation for the overall reaction
Revise - j
a qualitative explanation of the effect of temperature change on the rate of a reaction and hence the rate constant (see 3.2.2 f–g)
Revise - k (i)
the exponential relationship between the rate constant, k and temperature, T given by the Arrhenius equation, k = Ae^(–Ea/RT)
Revise - k (ii)
determination of Ea and A graphically using: ln k = –Ea/RT + ln A derived from the Arrhenius equation
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