### IODINE CLOCK COURSEWORK A LEVEL

A single set of reaction rate data at a temperature of K. From runs i and ii , keeping [B] constant, by doubling [A], the rate is doubled, so 1st order with respect to reactant A. The third graph is a plot of HI decomposition rate versus [HI] squared, and, proved to linear – the blue data line was pretty coincident with a black ‘best straight line’. A graph is drawn of CH 3 3 CCl concentration versus time. Deducing orders of reaction.

The numbers in bold show the factor change in concentration and its effect on the rate. From experimental results you need to know how the speed of a reaction varies with respect to individual reactant concentrations. There is another graphical way of showing the order with respect to a reactant is 1st order , but it requires accurate data showing how the concentration or moles remaining of a reactant changes with time within a single experiment apart from repeats to confirm the pattern. These examples do NOT involve graphs directly, but a ‘graphical’ section of examples has been added in section 5. The mathematics of 1st order rate equations units.

There is another graphical way of showing the order with respect to a reactant is 1st orderbut it requires accurate data showing how the concentration or moles remaining of a reactant changes with time within a single experiment apart from repeats to confirm the pattern.

Orders of reaction can only be obtained by direct experiment and their ‘complication’ are due to complications of the actual mechanism, which can be far from simple. Since the gradient ciursework changes with concentration, it cannot be a zero order reaction. Only then is it possible to derive a rate expressionwhich summarises what controls the speed of a particular reaction in terms of the corusework concentrationswhich is not necessarily all the reactants!

## Using the iodine clock method to find the order of a reaction.

From runs i and iikeeping [B] constant, by doubling [A], the rate is unchanged, so zero order with respect to reactant Lodine. A single courrsework of reaction rate data at a temperature of K. Here, the coincidence is not surprising, the chance of a ‘fruitful’ collision is directly dependent on both reactants initially colliding, its often the slowest step even in a multi—step mechanism and if there are no other kinetic complications, the orders of reaction do match the numbers of the balanced equation e.

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I’ve made the numbers quite simple to follow the logic of the argument.

The units of kthe rate constant. The table below gives some initial data for the reaction: This zero order reaction occurs when the enzyme invertase concentration is low and the substrate sucrose concentration is high.

From runs ii and iii. We can now examine theoretically, the effect of changing individual concentrations on the rate of reaction of a more complicated rate expression of the form. CH 3 3 C—Cl concentration. From the point of view of coursework projects the detailed analysis described above is required, but quite often in examination questions a very limited amount of data is given and some clear logical thinking is required.

Examples of obtaining rate data.

# The Iodine Clock – GCSE Science – Marked by

Kinetics of the cock decomposition of hydrogen iodide. Have your say about doc b’s website. This proved to be a curve – compare the blue rate data curve with the black ‘best straight line’ courtesy of Excel! The graph on the left illustrates the initial rate method for the formation of product.

The concentration of iodide, peroxodisulfate or an added catalyst e.

The orders of reaction are a consequence of the mechanism of the reaction and can only be found from rate experiments and they cannot be predicted from the balanced equation. So simplified rate data questions and iodjne solutions avoiding graphical analysis are given below.

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The data below are for the hydrolysis of 2—chloro—2—methylpropane in an ethanol—water mixture. Experimental results can be obtained in a variety of ways courseork on the nature of the reaction e.

# The Iodine Clock Investigation – GCSE Science – Marked by

This proved that the decomposition of hydrogen iodide reaction is a 2nd order reaction. You can think the other way round i. Analysing a single set of data to deduce the order of reaction. You may need to use aqueous ethanol as a solvent since the halogenoalkane is insoluble in water and a large volume of reactants, so that sample aliquot’s can be pipetted courzework regular time intervals.

The gradients A and B would be for two different concentrations of a reactant, the concentration for A would be greater than the concentration of B. The initial rate is taken as the positive tangent – gradient for the curve at the point 0,0.

## Iodine clock coursework level

A non-linear graph of concentration versus time would suggest first or second order kinetics. The graph below show typical changes in concentration or amount of moles remaining of a reactant with time, for zero, 1st and 2nd order.

Therefore it cloock possible to get a reaction time for producing the same amount of iodine each time.

Reminder [x] means concentration of x, usually mol dm