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CMY3709 Assignment 1 (DETAILED ANSWERS) Semester 1 2024 - DISTINCTION GUARANTEED
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CMY3709 Assignment 1 (DETAILED ANSWERS) Semester 1 2024 - DISTINCTION GUARANTEED
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6.1 : Rates of Reaction
A. What is the rate of reaction?
Definition: The decrease in concentration of a reactant per unit time or the increase in
concentration of a product per unit time. (Units: mol dm-3 s-1 / mol dm-3 s-1)
This can be understood from 2 perspectives.
1. Rate of product formation
2. Rate of reaction consumption
How to find the rat from a concentration - time graph at a certain point?
Use the GRADIENT :D
There are 3 types of rates of reactions that can be deduced…
I. Initial Rate
● Rate at start of reaction when an
infinitesimally small amount of reactant is
used up (basically at 0 when the reaction
first starts)
● Gradient of tangent at t = 0
● For most reactions, this is usually the
greatest. Reason?
○ Highest initial conc. of reactants
IB NitrogeNotes Chem 6
, ○ Thus, highest frequency of effective collisions
II. Instantaneous Rate
● Rate at any particular instant in time, any point along the graph
● Gradient of tangent at t = n (some time)
III. Average Rate
● Rate of reaction calculated from change in conc. of reactant/product over time
● Timeframe needed to calculate.
B. Experimental Procedures for Determining Rate of Reaction
Properties monitored during typical experiments (and methods to do so!)
● Concentration of product/reactant
● pH (acid/base consumed or produced)
● Vol. of Gas (production of gas)
● Change in mass (production of gas)
● Colour of reacting mixture (coloured reagents)
● Electrical conductivity of reacting mixture (change in # mol of ions)
Quenching
● What is Ǫuenching?
○ Samples of reaction mixture withdrawn at regular
time intervals
○ When withdrawn, the reaction has to be
significantly slowed down/stopped because conc.
reactants decreases.
○ Process of slowing/stopping reaction - Ǫuenching
● How to Ǫuench?
○ Adding large volume of cold solvent
■ Dilute + Reduce Temperature… 一举两得！
○ Add a quenching reagent
■ Reacts with reactants, (thus stops reaction)
○ Add an inhibitor / negative catalyst
Chemical Method - Titration
● I’m sure you know how this works.
● In essence, a sample is taken out at regular intervals, and some wizard potion is
added to it to determine the concentration at that specific time.
● Some examples:
IB NitrogeNotes Chem 6
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