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Rates of reaction.

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Introduction

RATES OF REACTION BY FAHAD ASHRAF Background Knowledge The rate of a chemical reaction is a measure of how fast the reaction takes place. In order for a chemical reaction to take place, the reactant particles must collide with each other, and a fixed amount of energy called the activation energy (Ea) must be reached. If a collision between particles can produce sufficient energy (i.e. if the particles collide fast enough and in the right direction) a reaction will take place. Not all collisions will result in a reaction. The rate of reaction increases if there is an increase in the total number of collisions. This is called collision theory (see diagram below). . The following factors affect the rate of a reaction: - Temperature The rate of a chemical reaction increases as the temperature increases. A rough rule of thumb, which applies to many reactions at around room temperature, is that a 10oC increase in temperature approximately doubles the rate of a reaction. Upon increasing the temperature, the particles move faster. This has two effects. As the particles are moving faster they will travel a greater distance in a given time and so will be involved in more collisions. Also, as the particles are moving faster a larger proportion of the collisions will be exceed the activation energy. ...read more.

Middle

From preliminary work, the following concentrations of hydrochloric acid will be used, 0.5M, 1.0M, 1.5M and 2.0M, and the volume of carbon dioxide gas will be measured in intervals of thirty seconds. Prediction: If the concentration of hydrochloric acid is doubled, the rate of reaction will also double. Theory behind prediction: If the concentration of hydrochloric acid is doubled, the number of acid particles per cubic centimetre will double, hence there will be twice as many collisions occurring between the hydrochloric acid and calcium carbonate particles per cubic centimetre. This will result in the rate of reaction increasing by a factor of two. This prediction will be tested by plotting graphs of time (s) against volume of carbon dioxide gas evolved (cm3) for the different concentrations of acid, and comparing the gradient of the graphs at a given time. If the rate of reaction doubles the gradient of the graph will double. The general shape of the graphs should be as shown below. The rate of reaction is greatest when the gradient is steepest, i.e. at the start of the reaction, as both the reactants are at their highest concentration. As the reaction precedes the concentration of the reacting substances decreases and the rate of reaction decreases, therefore the gradient becomes less steep. The reaction is complete when the graph becomes horizontal, i.e. ...read more.

Conclusion

Overall the results show good agreement with my predictions. CONCLUSION Overall the results showed good agreement with the predictions. This is beacause the experimental setup is reasonably accurate, and only a few problems were encountered. Although there are no anamolous results , a few points lie outside the line of best fit. The results where repeaed twice and the values were averged. In some cases there was not very good agreement between the two values. Due to time constraints the experiment could not be repeated for a third time. Had the experiment been repeated for a third time we could discard the value not consistent with the other two and hence obtain more accuarate results. The errors present in the experimental setup include errors due to parralex( can be avoided my take measurements at eye level), the presence of bubbles in the measuring cylinder and the reaction of carbon dioxide with water (to form carbonic acid). All these errors would give innacurate measurements of the volume of gas. These could be overcome by using a syring the collect the gas, rather than collecting the gass under water. Other errors include judgement errors and errors due to reaction times. This experiment could be exteneded by investigating the other variables which effect the rate of reaction, using different reactants and by using different experimental methods. Other methods include, sampling and titration and the use of a coloriemeter. ...read more.

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