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Rates of Reaction

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Introduction In this investigation I am investigating the reaction between hydrochloric acid and calcium carbonate (known as limestone). The rate of reaction is basically the speed a reaction takes place- meaning how long it occurs for. Chemical reactions only occur when reacting particles collide with each other with sufficient energy to react. The minimum amount of energy that causes them to react is called the activation energy - simply because it activates the reaction. There are many variables that need to be taken under consideration when measuring the rate of reaction. These can include catalysts, surface area, temperature or concentration of the liquid. In this case the dependant variable is the concentration of the liquid. These variables can either decrease or increase the rate of reaction. Theoretical Background When a reaction takes place it has to overcome a minimum energy barrier known as the Activation Energy. If the particles collide with less energy than the activation energy then nothing worth noting happens. "You won't get a reaction unless the particles collide with a certain minimum energy called the activation energy of the reaction." (Taken from www.chemguide.co.uk). Only those collisions, which have energies equal to or greater than the activation energy result in a reaction taking place. The reason why collisions have to overcome the activation is because every chemical reaction results in bond breaking. The activation energy is all about the breaking of the original bonds. So when the collisions between particles are relatively gentle there isn't enough energy available to start the process of breaking bonds and there the particles do not take part in a reaction. If the particles collide with less energy than the activation energy they simply bounce apart. Only those collisions equal to or greater to the activation energy react. What is the rate of reaction? The rate of reaction is the speed of the reaction. It is how quickly a reaction takes place. ...read more.


Just as four moles of hydrochloric acid will have will have eight times more particles than 0.5 moles of hydrochloric acid 2 moles of hydrochloric acid will have twice as much as particles as 1 mole of hydrochloric acid and so 3 moles of hydrochloric acid will have three times as much particle as 1 mole of hydrochloric acid. Low concentration of particles (for example 0.5 moles of hydrochloric acid). High concentration of particles (for example 4 moles of hydrochloric acid). How I predict my graphs to be: The graph for molarity 4 will be approximately as below compared to the graph on the right. The trend will be less steep for 0.5 moles. PLAN I plan to find out what affects the rate of reaction between calcium carbonate and hydrochloric acid. The variable I am going to change is concentration. These are the concentrations I am going to use: 0.5 mole dm3 1 mole dm3 2 mole dm3 3 mole dm3 4 mole dm3 In this experiment I am measuring the amount of gas given off. Because of this I am going to use he gas syringe to measure how much gas is produced. Once each test is started the amount of gas produced every 20 seconds will be recorded. Below is a diagram that shows how the gas is produced and measured using a gas syringe: Three tests will be carried out for each molarity. This is to see whether the experiment is well carried out or not. Anomalous results may rise. If on of the tests are wrong then there will be results which highly differentiate - and this suggests that the tests are wrong. Three tests carried out mean for each use of molarity the tests will be repeated 2 more times so I will have three different sets of results for each molarity for e.g. 3 tests for 0.5moles; 3 test for 1 mole etc... ...read more.


The experiment can be extended by using a bigger gas syringe which can hold more volumes of gas. This will be needed for use of larger concentrations. Also the experiment can be lengthened by experimenting for more than 120 seconds (2 minutes) the experiment could be extended to 180 seconds (3 minutes). This all would give a broader more useful and reliable set of results. One improvement that could've been made is checking the actual molarities. Although the bottle stated that the HCl was of a certain concentration it doesn't mean that there weren't any mistakes. If this was the cause then the HCl used may be 0.7moles other than stated 1 mole. The actual molarity of the HCl may be higher or below the molarity stated. An increase in molarity means an increase of the rate of reaction; alternatively a decrease in molarity means a decrease in the rate of reaction. This would highly affect my results because my results are basically conducting the rate of reactions using certain concentrations - this would prove my predictions wrong. I am pretty much sure the actual molarity wasn't different from the molarity stated because my results did not contain any anomalous results and so proved my prediction correct. Ways in which my investigation could have been improved: * Increase molarities to 5 moles and 6 moles etc... * Use a larger gas syringe * Use the water bath method * Extend experiment to 3 minutes/180 seconds * Conduct more tests instead of 3 * Check molarity before use My results have been very accurate. My predictions have all been proved correct which shows all the relative understandings of theories such as the collision theory. So as said before the higher the concentration the faster the rate of reaction. This is shown - the highest concentration used was 4 moles and so the rate of reaction was fastest. ...read more.

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Response to the question

Overall an exemplary piece of work for this level of qualification. Sets out in the introduction some of the science behind the rates of reaction and states what he is trying to measure. In the main body of text goes ...

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Response to the question

Overall an exemplary piece of work for this level of qualification. Sets out in the introduction some of the science behind the rates of reaction and states what he is trying to measure. In the main body of text goes into the science behind rates of reaction to a very concise and clear extent, and explains the science very well. Later on goes into the aim of the experiment which actually differs slightly from the intentions displayed in the introduction, so the aim should be rewritten to reflect the overall intentions of the experiment as they are only investigating the concentration of the liquid which is stated as the dependent variable, not what in general affects the rate of an experiment. Conclusion adequate and very detailed.

Level of analysis

The level of analysis is very detailed and consulted from a wide range of sources for this level. Able to set out the experiment well, and provides a well thought out and accurate evaluation and conclusion for this experiment that reflects a student at the top level of GCSE grades.

Quality of writing

Punctuation, grammar and spelling all fine. Writer communicates meanings very clearly and all of the chemistry is correct.

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Reviewed by skatealexia 02/03/2012

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