kinetics/ rate of reaction

simple rate equations

determination of rate equation

  • Created by: Damian
  • Created on: 12-09-09 13:53

kinetics RECAP

Rate= change in concentration / time for change to occour

collision theory A reactions will only happen if the reacting particles:

1, Collide in correct orientation and

2, have collision energy EQUAL TO or GREATER THAN the ACTIVATION ENERGY

Ea=minimum collision energy needed for the reaction to occur.

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RATE OF REACTION = rate of change of concentration of a named reactant or prouduct with respect to time.


rate is measured in mol dm-3 s-1 ( could be minutes or hours depending on the speed of reaction).

RATE DECREASES AS TIME PROCEEDS reactants get used up, fewer collisions, lower reactin rate.

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rate equations

RATE EQUATIONS = matematical equations showing How rate of REACTION varies with the Concentration of ANY Particular Reactant.

IN GENERAL , the rate eqaution for reactant "A" is in the form:

RATE = K[A]p

p= order of reaction 0,1 or 2

where A = the molar concentration ofreactant "A"

K= the Rate Constant for the reaction

power P= the Order reaction for A

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working out the RATE EQUATIONS

RATE =K [H2]a [NO]b

table 1 initial conc (mol dm-3) initial rate (mol dm-3 s-1)

ept H2 NO

1 0.01 0.025 2.4x10(-6)

2 0.005 0.0025 1.2x10(-6)

3 0.01 0.0125 0.6x10(-6)

ept 1 and 2 [NO] constant [H2] x2 ratex 2

so its first (1) order w.r.t [H2] a=1

ept 1+3 [H2] constant [NO]x2 rate x4 (22)

second order w.r.t [NO] b=2 overall order=3 (just add both together)

RATE= k [H2] [NO]2

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rate equation continued

experiment 1

K= RATE = 2.4x10(-6) = 0.384 mol-2 dm6 s-1

[H2] [NO]2 (0.01) (0.025)2

k= mol dm-3 s-1

(mol dm-3) (mol dm-3)2 or mol2 dm-6

those the same on top as buttom cancel each other out leaving

s-1 mol-2 dm6 s-1

mol2 dm-6

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