Kinetics - Rates of Reactions

First topic. Summarises how the rate equation is found and what each symbol means. Also gives information on zero - second order, including graphs.

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  • Created by: Harriet
  • Created on: 15-09-09 21:12

Kinetics - Rates of Reactions

Rate = Change in concentration / TIME for change to occur

THe change in concentration can b measured by:

  • Appearance of disappearace of colour
  • Volume of gas evolved
  • Changes in PH
  • Heat produced
  • Changes in pressure (reactions involving gases)

Rate Equation: is defined as the change in concentraton (of any reactants or products)with unit time

Order of Reaction: the power to which the concentrations of the reactants are raised to the rate equation

Rate = K[A] a [B] b

[ ] - stand for concentration

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Rates of reactions continued..

K = a constant for a particular reaction at a given temperature - known as the rate constant.

(any number raised to the power of 0 = 1)

Faster reactions have larger K values

A catalyst does not increase the K value - it causes a different reaction mechanism with a DIFFERENT K value

The only factor that affects the value of K is temperature

a + b - the orders. To get the overall order of the reaction, add all the powers together

Zero Order

If doubling the concentration of one reactant has no affect on the rate it is sadi to hav zero order w.r.t that reactant

Graph:

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First Order:

If doubling the [reactant] doubles the rate of the reaction then it is said to be forst order w.r.t [reactant] (i.e if bothe go up by the same number it is first order)

Graph:

Second Order:

If doubling [reactant] increases the rate by 4 then the reaction is said to be second order.

Graph:

Measuring Rates of Reactions:

Rate is measured in moldm-3s-1

The seconds can also be either minutes or hours depending on the speed of the reaction.

Rate decreases as time proceeds - the fewer collisions, the slower the rate of reaction

Initial Rate: the rate at the start of the reaction

Monitoring the rate can be:

1. Continuous

or

2. For intial rate only

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Measuring rates of reactions

Measuring Rates of Reactions:

Rate is measured in moldm-3s-1

The seconds can also be either minutes or hours depending on the speed of the reaction.

Rate decreases as time proceeds - the fewer collisions, the slower the rate of reaction

Initial Rate: the rate at the start of the reaction

Monitoring the rate can be:

1. Continuous

or

2. For intial rate only

4 of 4

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