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Enzyme Investigation

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Back Ground Information * A rate is anything per unit time. * Things that speed up a reaction are things like the increase of (temperature, pressure, and concentration). * The unit for concentration is (Moles/dm3). * Powdered substances react quicker because the have wide surface area. * The rate of a chemical reaction i.e. how fast a reaction goes can be explained using the collision theory. Collision Theory In a chemical reaction: - 1. Particles must collide 2. The collision must have enough energy within it, for the particles to reach the transition state and form products. 3. The particles must collide in the right orientation if products are to be formed. The more the number of collisions, the more the chance that the collisions will have enough energy to reach the top of the activation energy to form products. In general most of the collisions either never have enough energy to form products or the particles do not collide in the right orientation, therefore only a few particles go on to form products (Maxwell Boltzmann Theory - A Levels!). Factor that affects rates of reaction Since the particles -molecules or ions- must collide to react. There are several factors that directly affects reaction rate: > Temperature: a rise in temperature greatly increases the rate of reaction. The average kinetic energy of the particles is increased; a higher proportion of them have an energy greater than the activation energy required for the reaction, and the number of effective collisions is higher. This means that there would be more collisions per unit time. Hence this increases the chances that more collisions will have enough energy to reach the transition state. ...read more.


[A] [B]2 and the reaction is first order with respect to A, second order with respect to B, and third order overall. So the overall order of the reaction is the sum of the indices in the rate expression. All this has to be found experimentally because the orders of a equation do not necessary coincide with the figures used in a balanced equation. For example, potassium peroxodisulphate reacts with potassium iodide to form iodine. Ionically this equation is: S2O82-+2I- ?I2 + 2SO42- The rate equation is found to be: Rate of reaction = ? [S2O82-][I-] So the reaction is first order with respect to both peroxodisulphate and iodide ions, although from the equation you might think that it was second order (involving two ions) for the iodine. Determination of the orders if a reaction can be used to find out how it takes place. Finding the rate of reaction The rate reaction at a given moment is usually expressed as the amount of reaction taking place in unit time, and to find it the change of the concentration of one component of the reaction mixture is measured. Such characteristics as change of colour, volume of gas evolved, or change of pressure may be used. The rate found should be quoted in terms of the change used. For example: "Rate of reaction with respect to concentration of iodine" or "Rate of reaction with respect to oxygen involved". Consider the decomposition of hydrogen peroxide, catalysed by manganese dioxide: 2H2O2 (aq) ? 2H2O (l) + O2 (g) The oxygen evolved can be collected in a syringe and its volume measured at set time intervals (say fifteen second). A graph of the results can be plotted. ...read more.


* 0.1M sodium thiosulphate * Pen & paper * 250cm3 conical flask * 50?C thermometer Safety * Goggles * Lap coat * SO2 gas is dangerous it might cause asthma; therefore the experiment must be carried out in a well-ventilated room. Obtaining Evidence * Precise method. * Tabular presentation Concentration of HC (M) Vol. Of acid (cm3) Temp. (?C) Vol. Of thiosulphate (cm3) Concentration of thiosulphate (M) Time taken for cross to disappear Average Rate (unit/time) 0.0 30 20 30 0.1 0.2 0.4 0.6 0.8 1.0 Analysis * Two accurate graphs must be done by average observations * One of them is a time taken (sec) - Concentration of HCl (M) graph * It won't be a perfect curve and not a line * The other one is a Rate unit/time - concentration of HCl graph * Comments on line... This graph shows that as the concentration increases the time taken for the cross to disappear decreases. (a simple explanation to make you gain two marks) * For the other graph... This graph shows that as the concentration increases the rate of reaction increases. * To get your A* you must make it sound better. * Graphs must be accurate... units for each thing... title for each thing... Occupy as much space as possible in the graph paper. * Next paragraph, (in my background information I said that something doubles... therefore this doubles as well). Say also that these graphs are showing exactly what I needed. * On graph, pick four points, draw a line from the horizontal line until the graph's line towards each point chosen, then see the correspondent on the vertical line, then prove that they double. So if the first point was 0.3, the second is the double :0.6. (link it to your prediction). ...read more.

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