The rate at which a reaction occurs, or takes place, is affected by various factors, such as the temperature at which the experiment is conducted in, the pressure which is given, the surface area which is exposed, use of catalysts, and the concentration. In this investigation, I would be investigating the affect of surface area, or particle size, in the rate at which a reaction occurs. Background Information:
The more finely divided the solid is, the faster the reaction happens. A powdered solid will normally produce a faster reaction than if the same mass is present as a single lump. The powdered solid has a greater surface area than the single lump. Note: Why normally? What exceptions can there be?
Imagine a case of a very fine powder reacting with a gas. If the powder was in one big heap, the gas may not be able to penetrate it. That means that its effective surface area is much the same as (or even less than) it would be if it were present in a single lump. A small heap of fine magnesium powder tends to burn rather more slowly than a strip of magnesium ribbon, for example. Imagine a reaction between magnesium metal and a dilute acid like hydrochloric acid. The reaction involves collision between magnesium atoms and hydrogen ions.
How does surface area affect a chemical reaction?
If one of the reactants is a solid, the surface area of the solid will affect how fast the reaction goes. This is because the two types of molecule can only bump into each other at the liquid solid interface, i.e. on the surface of the solid. So the larger the surface area of the solid, the faster the reaction will be. Smaller particles have a bigger surface area than larger particle for the same mass of solid. There is a simple way to visualize this. Take a loaf of bread and cut it into slices. Each time you cut a new slice, you get an extra surface onto which you can spread butter and jam. The thinner you cut the slices, the more slices you get and so the more butter and jam you can put on them. This is "Bread and Butter Theory". You should have come across the idea in your biology lessons. By chewing your food you increase the surface area so that digestion can go faster. Bibliography:
1. "The Effect of Surface Area on Rates of Reaction." Chemguide: Helping You to Understand Chemistry - Main Menu. N.p., n.d. Web. 06 Nov. 2010. http://www.chemguide.co.uk/physical/basicrates/surfacearea.html 2. "Rates of Reaction." Gondar Design Science. N.p., n.d. Web. 06 Nov. 2010. http://www.purchon.com/chemistry/rates.htm
The collision theory states that the reactant particles must collide to create a reaction and form a new product. The rate of reaction depends on the successful collisions between the reacting particles. The more the successful collisions, the faster the reaction will occur. When a solid reactant is broken into tiny pieces or powder, its surface area increases. Increasing the surface area results in an increased exposure to the other reactant, thus increasing the number of collisions between the two reactants. And the higher the frequency of the total collisions, the greater the chances of effective collisions to take place, which in turn results to an increased rate of reaction.
The above graph shows that, the smaller the surface of the reactant, the more the time required for it to react. That is the reaction will be slow, as seen by the red line. On the other hand, the reaction is fast when the surface area is increased, as it requires less time to form the equal amount of product as when formed by a reactant with a smaller surface area. The blue line shows this. Thus I predict that the more the surface area, the faster the rate at which a reaction will take place. Due to the fact that the number of effective collisions will increase, which in turn will increase the rate of reaction, as per the collision theory. Variables:
Independent Variable: The independent variable in this experiment will...
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