# Rates of reactions - Sample Essay

A gauze and heatproof mat will be used while heating to avoid any damage to the equipment. Fair Test In order for my findings to be valid the experiment must be a fair one. I will use the same standard each time for judging when the X has disappeared. I will make sure that the measuring cylinders for the hydrochloric acid and thiosulphate will not be mixed up. The amount of hydrochloric acid will be 5cm each time, and the amount of thiosulphate will be fixed at 50 cm3. During the heating stage of the experiment,a constant temperature will be used throughout.

All of these precautions will make my final results more reliable and keep anomalies at a minimum so thus make the entire investigation more successful. Prediction I predict that as the temperature is increased the rate of reaction will increase. This means that both graphs drawn up in my analysis will have positive correlation, and will probably be curved as the increase in rate of reaction will not be exactly the same as temperature is increased. This can be justified by relating it to the collision theory. When the temperature is increased the particles will have more energy and thus move faster.

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Therefore they will collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier to reaction and thus react successfully. Collisions between reacting particles are therefore more likely to occur. All this can be understood better with full understanding of the collision theory itself: For a reaction to occur particles have to collide with each other. Only a small percent result in a reaction. This is due to the energy barrier to overcome. Only particles with enough energy to overcome the barrier will react after colliding.

The minimum energy that a particle must have to overcome the barrier is called the activation energy, or AE. The size of this activation energy is different for different reactions. If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure, or surface area. Concentration – If the concentration of a solution is increased there are more reactant particles per unit volume. This increases the probability of reactant particles colliding with each other.

Pressure – If the pressure is increased the particles in the gas are pushed closer. This increases the concentration and thus the rate of reaction. Surface area- If a solid is powdered then there is a greater surface area available for a reaction, compared to the same mass of unpowdered solid. Only particles on the surface of the solid will be able to undergo collisions with the particles in a solution or gas. The particles in a gas undergo random collisions in which energy is transferred between the colliding particles. As a result there will be particles with differing energies. TABLE OF RESULTS:

ANALYSIS: In this experiment I have found that as the temperature is increased the time taken for the reaction to take place decreases. This means the rate of reaction increasers as it takes less time for a reaction to take place, so more reactions/collisions take place per second. In the temperature experiment the time taken for a reaction to take place decreased by roughly 10 seconds for every 10i?? C increase in temperature. There is also a trend in the increase in rate of reaction as the temperature increases. The difference is always more or less 0. 02 s-1, with the same exception.

Using the graphs, with lines of best fit, I can draw a conclusion from my experiment. Firstly I can see that with the time graphs (that plot temperature against time taken for the reaction to take place) the graphs have negative correlation in both cases, meaning that as the temperature increased the time taken for the reaction to take place decreases. The time graph for the temperature experiment has a steep curve than, meaning that the decrease in time taken for the reaction was far more rapid. Temperature graphs have a positive correlation as the temperature increased so does the rate of reaction.

This is because when the temperature is increased the particles will have more energy and thus move faster. Therefore they will collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier to reaction and thus react successfully, and when solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. The size of this activation energy is different for different reactions.

If the frequency of collisions is increased the rate of reaction will increase. However the percent of successful collisions remains the same. An increase in the frequency of collisions can be achieved by increasing the concentration, pressure, or surface area. EVALUATION: Overall I believe my investigation has been fairly sucessful the results I have obtained support my initial prediction, yet some of the errors I have made have left room for improvement. The anomalous reults shown on my graph could be due to a number of factors, for one I may not I have been entirely accurate with the timing system I have used.

I only used one stopwatch (controlled by myself) and so time would have been lost (or made up) from the time I observe the first changes in the solution to the time I stop the clock. My own human reaction time may have been quicker or slower from experiment to experiment. Another factor that could have been effecting the progress of my experiment was the fact that after taking the conical flask out of the waterbath I did not check the temperature again to make sure bath had maintained its acuracy.

Any drop in temperature may have caused a varriation in my results. If I carried out this investigation again I think I would pay more attention to degrees of accuracy, I would also like to investigate the effects of concentration on the rate of a reaction as this would supply a more varried aray of data and may help me to understand different aspects of the ‘collision theory’. Although there are aspects that need improving in the experimentation rea of my coursework I am pleased with the overall product I have produced.

I believe some aspects of my experiments were sucessful allowing a fairly high degree of accuracy, for instance I always took full care to make sure that the conical flask used was thoroughly cleaned in between each experiment and the area in which I worked was a safe environment, all these factors will help me improve any future investigations I carry out.

BIBLIOGRAPHY: www. google. com The encloypedia  AQA science revision guide  “Chemistry counts” “The material world”.

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