IGCSE Chemistry for IB diploma coursebook Chapter6 Chemical kinetics's mindmap

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Chapter6 Chemical kinetics's mindmap

• 6.1 Collision theory and rate of reaction
  • What is ‘rate of reaction’?
    • Rate of reaction is the speed at which reactants are used up or products are formed.
    • Experiments to measure the rate of reaction
      • Measurement of the rate at which CO2 is produced
        • The bung in the conical flask (Erlenmeyer flask) is removed, the calcium carbonate added, the bung quickly replaced and the timer started. This experiment can be used to generate a graph of volume of carbon dioxide produced against time by noting the volume on the measuring cylinder every ten seconds and then plotting the data.
          • Make sure the measuring cylinder is erected or the amount of CO2 we observed will be incorrect,when calculating the rate of reaction,it will be affected too.
        • The reaction appears to finish at 90 s (Figure 6.4) because no more gas is produced after that. The average rate of reaction during the first 90 s can then be worked out as: average rate =change in volume/time =60.0/90 = 0.67 cm3 s−1 .
          • average rate can be worked out by looking at where gas stops producing(take the value of the volume at where gas stops producing.),then take the value of time at which gas stops producing.Finally,using the formula,average rate = change in volume/time,worked out the average rate.
        • The rate at any particular time is given by the slope (gradient) of the graph at that time. This can be worked out by drawing a tangent to the curve at that point (Figure 6.5). The gradient of the tangent is given by: gradient =change in volume/time =64/30 = 2.1 cm3 s−1 Therefore the initial rate of reaction is 2.1 cm3 s−1, which means that, initially, the gas is being produced at a rate of 2.1 cm3 per second.
          • Make a tangent line through the origin, find a time point you want to study on the X-axis, make a vertical line, and use the formula to solve the Initial rate.
        • Possible problems: with experiments like this include the fact that some gas is likely to escape before the bung is put on the flask (resulting in all values for the volume of carbon dioxide being lower than expected) and variations in the sizes of the calcium carbonate pieces.
      • Measurement of the rate at which the mass decreases
        • The rate of this reaction can also be determined by measuring the speed at which the mass decreases. The experimental set-up for this is shown in Figure 6.6. The mass decreases as carbon dioxide is given off. The data for this experiment are shown in Table 6.2, along with the resulting graph in Figure 6.7.
    • Rate of reaction defined
      • Rate of reaction is the change in concentration of reactants or products per unit time.
      • Some principles link to the rate of reaction defined
        • The reaction rate is related with the coefficient of each reactants or products.
      • The rate of reaction at any time can be found from a graph of concentration against time by drawing a tangent at the particular time and finding the gradient (slope) of the tangent, in a similar way to that shown
      • Factors affecting the rate of reaction:
        • 1.concentration 2.pressure 3.Surface area 4.Temperature 5.Catalyst 6.clock reaction 7.change in color 8.change in pH 9.change in conductivity
          • i. increasing the first five factors will all affect the rate of reaction to be faster.
          • ii. clock reaction is a type of chemical reaction that can be used to measure the rate of a reaction. These reactions have a visible change, such as a color change, that occurs at a predictable rate.
          • iii. change in color can be measured by using the colorimeter，we can also speculate the color change by memorising the color of special substances,e.g:Cu(2+),Fe(3+),I2,Br2,KMnO4.
          • iv. change in pH can be measured through Measuring the concentration of hydrogen ion in the solution.(more hydrogen ions means the concentration higher.),then use the equation of pH = - log10([H+]) to calculate to determine the change in pH of the reaction.Or we can determine it by knowing the general pH for the reactants and the products,we can also determine it.But the simplest way to see the change in pH is to use Litmus test solution.
          • v. the change in conductivity can be determined by calculating the change of valence of both reactants and products(considering the change of both cations and anions.)
  • 6.1.2 Collision theory
    • three principles of collision theory
      • This states that for a reaction to occur particles must collide;
      • The first condition: a collision must involve more than a certain minimum amount of energy
        • Particles must collide with sufficient energy in order to react. The minimum amount of energy that colliding particles must possess to result in a reaction is called the activation energy (Ea). If two particles with less than the activation energy collide, they will just bounce off each other and no reaction will result; however, if the particles have energy greater than or equal to the activation energy then, assuming the orientation of the collision is also correct, the particles will react. A collision that results in a reaction is called a successful or effective collision.
      • The second condition: molecules must collide with the correct orientations.
        • If molecules do not collide with the correct orientation they will not react (Figure 6.13). Not every collision with energy greater than the activation energy results in a reaction,it either depends on whether the molecules are collided with the correct orientation.
    • Factors affecting reaction rate
      • 。concentration of reactants • pressure for (reactions involving gases) • surface area of solid reactants • temperature • catalysis. These will be considered in turn.
        • concentration
          • more particles in acertain volume,the particles collide more often(collision frequency increases.)in a certain time.
        • surface area
          • Area increases——more contact——higher probability of collision——collision frequency increases——rate of reaction increases.
        • temperature
          • T increases,kinetic energy increases,more particles have energy more than activation energy,chances of successful collision increases——rate of reaction increases.
        • pressure
          • concentration of gas increases——collision frequency increases——rate of reaction increases.
        • catalysis.
          • increases the rate of reaction by lowering the activation energy to let more particles can have successful collision.
• explain through collision theory
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