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Rates of Reaction

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Rates of Reaction The rate of a reaction can be defined as the speed at which a reactant is lost, and/or the speed at which a product is formed in a chemical reaction. All chemical reactions happen at different rates. Explosions are extremely fast, whereas rusting is extremely slow. There are five factors that affect the rate of a reaction. These are: * Temperature * Surface Area/Particle Size * Pressure * Concentration * Catalysts In our everyday lives, we usually want to slow reactions down, rather than speed them up. For example, we store food in fridges or freezers to slow any reactions down which would otherwise make the food rot. Aging is a process that many people want to slow down. Scientists have blamed the appearance of wrinkles on free radicals in the skin. They have also found out that using antioxidant creams helps slow the aging of skin down. Some paints contain antioxidants, called corrosion inhibitors, which slow down the oxidation of iron. The Collision Theory This kinetic theory will help me to explain the factors affecting the rate of a reaction. ...read more.


and 0.25M hydrochloric acid (HCl). I will draw a cross on a piece of paper, and place it underneath a conical flask containing the HCl. I will then add the Na2S2O3 to the conical flask and swirl the flask to mix the solutions. This will produce a pale yellow precipitate of sulphur. I will also start to time how long it takes for the solution to turn cloudy enough to obscure the cross, using a stop-clock. I will use five different solutions, each with a total volume of 60cm3. I will keep the volume of HCl constant, at 10cm3. Therefore I will increase the Na2S2O3 by 10cm3 each time. The temperature must remain the same. Below is a diagram of the apparatus: Preliminary Experiment I decided to carry out a preliminary experiment to help me choose the best variables for my main investigation. I did four tests in all. For the first three tests, I used a total volume of 50cm3, however I changed this volume to 60cm3, because the rate was slightly faster than I wanted it to be. The concentration of HCl was at a constant of 10cm3. ...read more.


10 10 20 20 30 30 70 70 18 17 18 17 4. 10 10 10 10 40 40 45 47 17 17 17 17 5. 10 10 0 0 50 50 33 30 18 18 18 18 To calculate the rate and relative rate of reaction, I have used the following methods: Concentration of HCl = concentration x volume = 0.25 x 10/1000 = 0.0025 moles Concentration of acid at the start of the experiment = Moles of acid / total volume = 0.0025/0.06 = 0.042 Concentration of Na2S2O3 = initial volume/total volume x 0.25 e.g. 20/60 x 0.25 = 0.83 Rate = 1/time e.g. 1/99 = 0.010 Relative Rate = Rate/slowest rate e.g. 0.004/0.004 = 1 I have tabulated the results from these calculations: Conc. of HCl Conc. of Na2S2O3 Average Time (s) Rate (mol/cm3/s) Relative Rate 0.042 0.042 210 0.004 1 0.042 0.083 99 0.010 2.5 0.042 0.125 70 0.014 3.5 0.042 0.166 46 0.022 5.5 0.042 0.208 31.5 0.032 8 I have plotted a graph showing the relative rate as the concentration of sodium thiosulphate increases. From the line of best fit, I can see that they are directly proportional. Therefore my prediction appears to be correct. Extension Experiment For my extension experiment, I decided to test how absorbing ...read more.

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    The acid will be constant at 2.00moldm-3. * Volume of reactants. This will be kept constant as far as possible. 5cm3 of acid and 50cm3 of thiosulphate will be used throughout. * Any stirring or swirling of the mixture necessary to make the cloudy suspension develop evenly.

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