Reaction rate, catalyst & industrial chemistry 1.3

Task 1 – Carry out an experiment to investigate how temperature and concentration affect the rate of a chemical reaction. [P5]

Aim

• Observe the effect of temperature and concentration on a chemical reaction.

 Method 

• 50cm³ of potassium iodide was added to a 250 cm³ beaker.
• The same volume of starch was added to a 250 cm³ beaker.
• The two solutions are mixed together by pouring one beaker into another until the two substances are both thoroughly mixed.
• The time for a reaction to occur is noted.
• This experiment is repeated with Solution A (potassium iodide) at different temperatures; 25C˚, 30C˚, 40C˚, 50C˚ and 60C˚.
• Finally solution A is diluted to half its concentration and the time for a reaction to occur is noted.

Results 

Solution A (potassium iodide)	25C˚	30C˚	40C˚	50C˚	60C˚
Solution B (starch)	Solution B remains at a constant room temperature.
Mixed solutions	5 min	3 min	2min	N/A	N/A
Diluted solutions	10min	N/A	N/A	N/A	N/A

 

Conclusion 

As the temperature of the solution increases, the length of time of the reaction decreases. This is the direct effect that temperature as on the rate of a reaction, as it increases the particles move faster thus are involved in more collisions (collision theory), this in turn as the effect of reducing the energy activation (energy needed for a reaction to occur); increasing the rate of the reaction.

Regarding the dilution of solution A and its effects on the rate of the reaction, it is apparent that as the concentration of the solution is smaller the rate of the reaction increases.

Task 2 – Use the results to identify what factors affect the rate of a chemical reaction [P5]

Temperature

• Affects the rate of reaction by making particles move faster, thus increasing the rate of collision and more collisions affect the energy activation needed.

Concentration

• Affects the rate of reaction by increasing the rate of collision as particles become closer or further apart depending on the concentration rate affecting the rate of reaction.

Surface Area

• Affects the rate of reaction by increasing or decreasing the amount of space between particles (changing their exposure), affecting the rate of collision and so the rate of reaction.

Catalyst

•  Affects the rate of reaction by reducing the energy activation needed and thus increasing the reaction rate.

Task 2 – Explain how the factors in task 1 affect the rate of industrial reactions (use the collision theory in your answer). [M5]

The factors in task 1 all affect the rate of reaction in some way, by using them appropriately and by that I mean combining them with certain chemicals to achieve a desired effect, it is possible to significantly reduce the barrier which would make a given reaction hard to obtain or impossible without a given catalyst.

For example, using a catalyst to reduce the activation energy needed for certain chemical reactions e.g. platinum can be used as a catalyst in the reaction between sulphur dioxide and oxygen to make sulphur trioxide. The molecules of sulphur dioxide and oxygen are absorbed on the surface of platinum molecules. Through this process they inevitably become closer, thus more likely to collide and react with other, demonstrating how a catalyst can increase the energy activation of a chemical reaction.

Temperature can be used to increase the collision rate between particles as demonstrated by its use in chemical reactions with chemicals which do not have enough energy to react in their current state such as the experiment performed in task 1.

Concentration affects the rate of collision by increasing the amount of molecules in a given area thus increasing the likelihood of collisions as demonstrated by the experiment done in task 1.

Surface area affects the rate of reaction by changing the area of space available and thus exposing more particles which increases the collision rate.

In conclusion, the factors mentioned in task 1 and above have a direct effect on the rate of industrial reaction as they increase the amount of particles exposed to each other and thus increase the rate of collision as explained by the collision theory.

Task 3 – Analyse how these different factors affect the yield (produce) of industrial reactions. In industry you want maximum production from minimum chemicals. So getting the factors that cause a change is very important. [D3]

The rates of chemical reactions are affected by factors as demonstrated above but these not only affect the rate but also the yield of reactions. The decision on whether to increase a certain factor is based on the effect it has on the reactant and the potential benefit that would occur if said factor was used.

For example if temperature was used as the factor and its effect on the reactant were studied. Then based on these findings and whether or not they were beneficial in terms of cost and viability then it would most likely be used as it would make financial sense.

Not all factors are beneficial in terms of producing maximum yield and not all beneficial factors increase maximum yield in any variable. They have to be studied under different variables which include different values (e.g. temperature difference 200-300) and in conjunction with additional factors to find the conditions in which a reactant would produce the maximum yield possible with the least amount of chemical and possibly the minimum degree of factors as demonstrated in the Haber process for making ammonia.

The Haber process makes ammonia to an industrial scale by using certain factors at a specific degree in order to maximise yield. The higher the temperature and pressure when making ammonia, the higher faster the reaction will be. However this does not equate in higher yield and financial or facility viability (the latter because increasing the temperature and pressure becomes harder as it increases). As a result the amount of temperature and pressure used is not the highest or lowest possible but the point at which it becomes either unviable to increase either factors, because the resulting product is inferior to the cost of increasing the factors or does not fully maximise yield, financial or available resources before cost to yield ratio are passed beyond viability, which would be the case if the factors were at a lower intensity than the ideal point (the one which produces maximum yield a the best cost to yield ratio on an industrial scale in this scenario).

The Haber process is also a good example of how atom economy works, in this chemical reaction 100% of the reactants will be used to make ammonia because any unreacted gas (nitrogen and hydrogen) will be recycled and reused to form ammonia. A bad atom economy would be characterised by the reactants ending up as waste product (one which wouldn’t be the primary focus of doing the chemical reaction) as would be the case in the production of bromine with some chlorine and sodium atoms ending up in the form of sodium chloride.

In conclusion, the yield of chemical reaction is affected by the factors it is used in conjunction with, but its viability is defined by which varying degree said factors are used in which is why studies are done to understand how factors and reactants interact with each other and how this changes depending on the amount of factors or chemicals used (relative to each other). While atom economy is defined by the waste generated from a chemical reaction which would not be recycled (reused in the same chemical reaction). Yield and atom economy are thus directly related because the yield percentage defines whether or not the product of a chemical reaction is regarded as bad or good and vice versa atom economy can define the yield of a chemical reaction.

Bibliography

• GCSE Core science GCP
• BTEC level 2 Applied Science Edexcel 2010
• http://en.wikipedia.org/wiki/%5BReaction rate, chemical kinetics, Haber process, Reaction rate, Combustion]