# Rates of Reaction

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Orders, rate euations, & rate constants

• Rate = Change in concentration / Time
• [Moldm-3 s-1]

Orders of reaction

• Zero order - concentration has no effect on rate. // First order - Rate ~ [A]1 // Second order - Rate ~ [A]2 - i.e if concentration of A doubles, reaction rate increases by a factor of 4 (2^2)
• Overall order = Sum of orders with respect to each reactant. i.e. Overall order = ^m + ^n.
• Zero order reactants are omitted from the rate equation.
• You can work out orders from experimental data from when concentration increases what is the effect on the intitial rate (Look for table of results.).

The Rate equation & the rate constant

• Rate = K[A]^m[B]^n // K = Rate constant, [A] = Concentration of A, ^m = Order with respect to A
• K = Rate / [A] [B]  // To work out units cancel common units and express what is left i.e Moldm-3S-1 / Moldm-3 = S-1

Concentration - time graphs

• Plotted from continuous monitoring i.e. gas collection, mass loss, & colour change.
• In a colorimeter wavelength of light passing through coloured solution is controlled using a filter. Amount of light absorbed measured. Steps are as follows: Zero the colorimeter with water, Measure absorbance of standard solution, plot calibration curve (can covert absorbance into [A]), take experimetnal absorbance readings at timed intervals, & plot conc