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Friday, 28 March 2014

Topic 16.1: Rate expression

16.1.1 Distinguish between the terms rate constant, overall order of reaction and order of reaction with respect to a particular reactant

Rate is measured as the concentration, mass or volume (or anything else that can be directly related) of reactants or products changes with time. Rate constant is a constant for a particular reaction at a specific temperature.

Order of reaction with respect to a particular reactant is the power to which its concentration is raised in the rate equation. The overall order for the reaction is the sum of the individual orders for all reactants



16.1.2 Deduce the rate expression for a reaction from experimental data

Rate = k [A] [B]

Find the concentration of B that is constant. Find the change in [A] compared to the initial rate of reaction. Thus determine the order of reaction. Zero-order has no effect. First order is direct proportional. Second order is proportional squared. Repeat to find B as well.

Then conclude the rate expression

Rate = k [A]^n [B]^m


16.1.3 Solve problems involving the rate expression

After finding the rate expression. Input all the date into the equation to find the rate constant.

Be sure to get the state symbols correct.


  • Zero order
k = mol dm^-3 s^-1


  • First order
k = s^-1
  • Second order
k = mol^-1 dm^3 s^-1
  • Third order

k = mol ^-2 dm^6 s^-1


16.1.4 Sketch, identify and analyse graphical representations for zero-, first- and second-order reaction

Simply state the graphical representations. Such as, e.g., in zero-order reactions, the concentration has no effect to the rate.

Zero

First

Second



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