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Investigate various ways of increasing the rate of a chemical reaction and evaluate which has the greatest effect.

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Introduction

Chemistry Investigation by Yasir Al-Wakeel Aim: Our aim is to investigate various ways of increasing the rate of a chemical reaction and evaluate which has the greatest effect. Planning: Introduction A chemical reaction is the process by which atoms or groups of atoms from a certain substance react with those of another resulting in a product/s which has a changed molecular composition. A typical chemical reaction is of the form: A + B C + D in which A and B are the reactants and C and D are the products. Rate is commonly described as a measure of the change that happens in a single unit of time. The measure of rates is very important to the average person and is commonly used in everyday life. The table below illustrates some everyday rates of change (figures provided are approximations): Example Rate Travelling to school by car 40 miles per hour Travelling to school by foot 4 miles per hour Water coming out of upstairs tap 70cm3 per second Water coming out of downstairs tap 90cm3 per second Therefore if you were in a hurry to get to school you would be better off choosing the car if this option were available. Similarly if you were given a few minutes notice before your water was to be cut off you would be better off going downstairs to fill up containers for storage. Faster and slower are the two main ways of describing rate. And thus, with regards to chemical reactions, the rate of a chemical reaction is a measure of how fast or how slow it takes place. The unit for the rate of reaction is s-1 i.e. the reciprocal of time. Some reactions can be extremely fast such as a detonation1, an example of which being the oxidation of trinitrotoluene- commonly known as TNT. On the other hand some reactions may take a very long time such as the common process of rusting.2 The study of the rates of chemical reactions and their mechanisms is known as chemical kinetics. ...read more.

Middle

Thus we may predict that increasing surface area will increase the rate of reaction, however as there are several factors that will be altered quantifying this prediction presents some difficulty. Apparatus: * Safety goggles and plastic gloves * Test-tubes * Top-pan balance * Measuring cylinder * Scalpel * Test-tube rack * Stop-clock * Bunsen burner, tripod and gauze * Displacement can * Funnel * Spatula Plan of investigation: Before we begin the investigation it is essential that we take various safety precautions. These shall include wearing safety goggles for eye protection and wearing plastic gloves to protect our hands as the hydrochloric acid is corrosive. It is also crucial that we keep our area used for experimentation tidy to prevent accidents. It is important to keep the reactants separate whilst setting up the apparatus so that the starting time of the reaction can be measured accurately. The investigation shall proceed in three main parts, each dealing with one different independent or input variable. We shall first consider that of concentration. It is likely that we will have enough time to carry out the experiments to determine the effect of hydrochloric acid on the rate using five different concentrations. With the results of five different concentrations, I believe our data will be sufficient to evaluate our predictions. However our data would be more accurate if we used the method of averaging, i.e. repeat each experiment several times which is useful in order to reduce experimental error. However, it is unlikely that we will have sufficient time to use the method. In order to receive a fair set of results regarding the effect of concentration the following variables shall be constant: 1 Amount of Hydrochloric acid -15cm3 2 Form of calcium carbonate, i.e. solid or powder-(powder) 3 Temperature - room temperature 4 Mass of calcium carbonate (0.25 grams) The steps taken shall be as follows: Step1) ...read more.

Conclusion

To match this we would have had to increase the temperature by 40K or increased the concentration by a factor of 22. Changing surface area was probably the easiest and most practical as well as the most effective. On a whole we may say that our experiment has proved that increasing surface area, concentration and temperature all increase the rate of reaction. However, we may only say this regarding the reaction that we have considered. Since, although we may have found that increasing these factors increases the rate of reaction this may not necessarily be true for all reactions. Indeed, as we mentioned, in reactions of first order with respect to one of the reactants, altering concentration has no effect. Also in enzyme catalysed reaction, above a certain temperature, increase in temperature in fact has a negative effect on the rate of reaction. Provided that the equipment needed is available, we may repeat the experiment using different methods of analysis. The conductmetric or measuring gas evolved methods, as explained, may be worth trying. Also, different types of reactions may be considered. For example in considering the effect of temperature, we may consider explosive reactions or enzyme catalysed reactions, a graph of reaction rate against temperature would look something like as follows: most reactions explosive reactions enzyme catalysed reactions It may also be of some use to consider other factors that effect the rate of reaction such as catalysis and light. A catalyst is a substance which alters the rate of reaction without itself undergoing any permanent change. This is as a provides a new reaction path for the breaking and rearrangement of bonds, a path that in most cases has a lower activation energy. Using a basic analogy, we may say that a catalysed reaction is similar to a pole-vaulting event in which the bar has been lowered and hence many more athletes get over it. Light too has an effect on certain reactions. Photosynthesis and photography are two common examples. ...read more.

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