Rates of reaction C6

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  • Rates of reaction
    • Rate of chemical reaction is how fast the reactants are changed to products
      • Slow reaction: iron rusting or chemical weathering
      • Medium   speed reaction: metal magnesium causing bubbles in acid
      • Fast reaction: burning or explosions
    • Graph (Product formed over time)
      • Steeper the line faster the RoR (rate of reaction) lines becomes less steep as reactants are used up
      • Quickest reactions have steepest line and become flat in the quickest time
    • Collision theory (rate of reaction depends on:...)
      • Collision frequency: how often they collide, more collisions faster the reaction
      • Energy transferred: particles need to collide with enough energy for it to be successful -activation energy (minimum energy needed to break bonds)
    • Depends on 1. temperature 2. con-centration.  3. Pressure 4.surface area 5. Catalyst
      • Temperature : increase temperature means particles move faster as they have more energy so they collide more frequently with enough energy
      • Con-centration and pressure: more concentratedmeans more particles in the same volume (same for pressure but gases) mean more frequent collisions
      • Surface area: breaking a reactant from a solid into smaller pieces increases surface area, meaning for the same volume of solid there’s now more area for collisions to occur
      • Catalyst: -speeds up reaction without being used up or affecting the overall equation- they decrease activation energy by providing a alternative pathway with lower activation energy so more successful collisions with enough energy
    • Measuring RoR
      • Rate of reaction is amount of reactant used or amount of product formed over time
        • Reactant/product is gas = cm^3 or a solid = g. Time in s. Unit for rate is either cm^3/s or g/s or for moles mol/s
      • Reactant/product is gas = cm^3 or a solid = g. Time in s. Unit for rate is either cm^3/s or g/s or for moles mol/s
      • Can be measured in three different ways: 1. Precipitation or colour change 2. Change in mass 3. Volume of gas is given off
        • 11. Colour change/ precipitation = visual change from transparent to opaque solution if product precipitates. From coloured to colourless solution (or vice versa)
          • Measure how long it takes for a cross to become invisible through the solutionn or how long it takes for colour change
        • 2. Change in mass= reactions the produce a gas means speed of reaction can be measured using a mass, quicker it takes for the mass balance to drop faster the reaction
          • Take measurements at regular intervals to plot a graph, it’s the most accurate method however the gas is released into the room
        • 3. Volume of gas= uses a gas syringe to measure volume of gas given off. More gas in given time interval faster reaction.
          • Take measurements at regular intervals to plot a graph, however if reaction is too vigorous the plunger will blow out of the end of the syringe

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