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# Detail, with appropriate scientific theory, the five main factors that affect the rate of a reaction

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Introduction

Detail, with appropriate scientific theory, the five main factors that affect the rate of a reaction A chemical reaction involves the breaking of bonds within the reactants and the creation of bonds to form products. Different bonds have different strengths so the energy required for various reactions to occur is different. The rate at which a reaction progresses is controlled by five main factors: - concentration, pressure, temperature, surface area and catalysis. A reaction profile is a graph that shows the energy changes involved during a reaction against time. The basic structure for an exothermic reaction is: - The graph shows that in the intermediate transition stage the reactants have gained more energy from their original form, and then go on to another energy level as products. The graph shows the activation energy required and the energy released. For an endothermic reaction, the reaction profile is similar except the products finish on a higher energy level, thus showing that energy has gone into the reactants to form the products. The collision theory is a theory used to explain rates of reaction. ...read more.

Middle

Also they will be moving more rapidly so the frequency of collisions will be greater resulting in more reactions and thus a higher rate of reaction. The molecules in a gas or liquid do not all have the same kinetic energies since they are moving with different speeds. The distribution of their speeds is called the Maxwell-Boltzmann distribution. The graphs that can be drawn to display this show, why at higher temperatures the rate of a reaction increases. The graph shows that at any temperature, only a few molecules will have very high or very low energies, with most having a value around a mean peak value. As the temperature increases the curve broadens out and the peak value drops moving towards a higher energy level. The area under each curve represents the number of molecules and is constant for each curve. The graph shows that to the right of the E act line, the molecules have enough energy for a reaction to occur. At the higher temperature (T3) a high proportion of the molecules have enough energy to react so the rate of the reaction is higher than at low temperatures (T1) ...read more.

Conclusion

They are generally only required in small amounts. They usually work by providing an alternate route from reactants to products, which has lower activation energy. The simplified reaction profile for such reactions is: - The graph shows simply that with the aid of a catalyst the activation energy required for the reaction is lowered so more of the molecules will have the energy required so the reaction will progress at a faster rate. An example of a catalysed reaction is that between peroxodisulphate ions and iodide ions: S2O82- (AQ) + 2I-(AQ) 2SO42-(AQ) + I2 (AQ) This reaction can be catalysed by Fe2+ ions, two reactions occur: S2O82- (AQ) + 2Fe2+(AQ) 2SO42-(AQ) + 2Fe3+(AQ) Followed by: 2Fe3+(AQ) + 2I-(AQ) 2Fe2+(AQ) + I2 (AQ) The catalyst is changed in the intermediate stage but at the end of the reaction is back in its original state. A reaction profile can be drawn for this reaction although it only shows a theory as to how the process works: - The graph shows the reactants and products along with the two-step intermediate stage where two reactions occur. Overall this reaction is exothermic. Andrew Roberts ...read more.

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