Rates of reaction

8.1 Rates of reaction

• Rate of reaction tells you how fast the reactants turn into products. Rate of reaction must be fast enough to make it quickly but safely
• To work out rate of reaction you can find out how quickly:
  • the reactants are used up as they make products
  • or, the products of the reaction are made
• mean rate of reaction = quantity of reactant used or quantity of product made / time
• To measure the increasing vol. of gas given off, collect the gas and measure the vol. given off at time intervals
• To measure the decreasing light passing through a solution measure the time it takes for a cross to disappear as a precipitate appears in solution
• To measure the decreasing mass of a reaction mixture, measure and record the mass of a reaction mixture as it takes place. e.g. put conical flask on top-pan balance w marble chips and HCl acid in it, w/ cotton bung on top

8.2 Collision theory and surface area

• Temp., surface area of solids, conc. of solutions or pressure of gases and presence of a catalyst all affect the rate of a reaction. Reacting particles must collide w/ enough energy to cause a reaction to take place (collision theory)
• Reactions are more likely to happen between reactant particles if you:
  • increase the frequency of reacting particles colliding w/each other
  • increase the energy they have when they collide
• Increasing the surface area of a metal increases the rate of reaction because more of the solid in powder form etc increases how much of the solution the powder is exposed to. The smaller the size of the pieces of a solid material, the larger its surface area to volume ratio

8.3 The effect of temperature 

• Increasing temp. increases rate of reaction because:
  • particles collide more often
  • particles collide w/more energy
• Heating up a substance transfers energy to it so the particles move faster and collide more frequently, so there's more chance the particles will react
• An increased proportion of particles exceeding the activation energy has a greater effect on rate that the increased frequency of collisions

8.4 The effect of conc. and pressure

• Statues are made of limestone, which mostly contains marble and calcium carbonate, which react w/ acids, leading the statue to crumble. Rate of reaction's increased because the conc of acid in rainwater has increased.
• It increases rate of reaction because there are more particles of the reactants moving around in the same…