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The reaction between sodium thiosulphate and hydrochloric acid:Looking at the graph the order of reaction established is 1st order

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Interpretation Investigation 1:the effect of concentration changes To summaries the results of the investigations the rate of reaction is used in the form of a rate equation. A rate equation shows how changes in the concentrations of reactants affect the rate of a reaction. An example of a general reaction for which x mol A react with y mol B to form products: xA + yB? products The rate equation is expressed in this form: Rate = k[A]n [B]m Where [A] and [B] represents the concentrations of the reactants in moles per litre. The powers n and m are the reaction orders. Therefore the reaction above is order n with respect to A and order m with respect to B the overall order is (n+m).The rate constant, k, is only constant for a particular temperature. The reaction between sodium thiosulphate and hydrochloric acid: Looking at the graph the order of reaction established is 1st order. Na2S2O3(aq) + 2HCl(aq) S(s) + SO2(g) + H2O(l) + 2NaCl(aq) Has a rate equation of the type: reaction rate = k [Na2S2O3]1[HCl]1 = k [Na2S2O3] [HCl] The reaction is first order with respect to Na2S2O3 and is first order with respect to HCl. ...read more.


+273 1/temperature= 1/k 10 0.1 s-1 -2.3 20 293 (20+293) 0.003412969 If you plot a graph of lnk rate against 1 Temperature (Kelvin) The slope of graph = -Ea R The activation energy can be calculated from the gradient: Therefore Ea (activation enthalpy) = -Slope ? R R= 8.314 kJ mol-1 1000 The activation enthalpy from the effect of temperature on the rate is 49.4 kJ mol-1 . Large activation energy (49.4 kJ mol-1) is only a small number of pairs of molecules that have enough energy to pass over it each second and turn into products, so the rate of reaction is slow. The data book literature value for the uncatalysed activation energy is 48 kJ/mol, this activation enthalpy is slightly lower than the one obtained from this experiment. Activation energy is the minimum energy required before a reaction can occur. You can show this on an energy profile for the reaction. For a simple over-all exothermic reaction. The Maxwell-Boltzmann Distribution The Maxwell-Boltzmann curve describes the distribution of the kinetic energies of molecules. At each collision, energy is transferred between the particles, so the particles are continually changing their energies. Maxwell-Boltzmann distribution diagram : Only those particles represented by the area to the right of the activation energy will react when they collide. ...read more.


3 for each concentration (5 conc.). The expected volume needed for method A would have been 750cm3 of sodium thiosulphate and hydrochloric acid measured in a volumetric flask. Whereas method B, using test tubes I only used 10cm3 and repeated it three times, overall volume used for sodium thiosulphate and hydrochloric acid was 250cm3. Evaluation Overall the investigations were a success. sufficient data was obtained to create graphs and to support conclusions. Percentage area Percentage Error = Error ?100 Reading Percentage error of 250cm3 volumetric flask: Error = 0.2cm3, therefore % error = 0.2 ? 100 = 0.08% 250 Percentage error of 25cm3 pipette: Error = 0.06cm3, therefore % error = 0.06 ? 100 = 0.24% 25 Percentage error of weighing scale: (sodium thiosulphate) Error = 0.005, therefore % error = 0.005? 100 = 0.08% Error ? 100 6.20 Mass Potential errors: All the systematic errors in the experiment are minimal. Another error which may have interfered with the experiment is human error, such as: * Accurate measurements of volume * Reading for the cross to become obscured * Reading the thermometer Potential improvements: * To use better instruments to produce accurate measurements such as an electronic pipette which you can type and enter your desired volume. * Repeating the same experiments with different acids, to check whether the pattern is general to all acids or not. * ...read more.

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