collision theory

• Temperature is a factor that affects reaction rates. An increase in temperature generally leads to an increase in reaction rate.
• Collision Theory explains the rate of a chemical reaction:

  • For particles to react, they must collide
  • Chemical bonds must be broken during the collision, requiring activation energy
  • Particles must collide in the correct orientation for a reaction to occur
• Activation energy is the energy required to break chemical bonds during a reaction
• To increase the rate of a reaction, one method is to increase the concentration of the reactants:

  • Higher concentration means more reactant particles in the same volume, increasing the chance of collisions
  • Increased frequency of collisions leads to more effective collisions and a higher reaction rate
• In reactions involving gases, increasing the gas pressure can also increase the rate of reaction:

  • Higher pressure makes gas particles closer together, increasing collision frequency
  • More collisions lead to more effective collisions and a faster reaction rate
• Chemical reactions can only take place when the reacting particles collide with each other and the collisions must have sufficient energy
• The rate of a chemical reaction is determined by the frequency of successful collisions, where frequency means the number of successful collisions per second
• The surface area of a solid reactant affects the rate of a reaction because particles in solution can only react with particles on the surface of the solid
• Increasing the surface area of a solid reactant leads to more collisions per second, thus increasing the rate of the reaction
• Smaller sized blocks of solid reactant have a greater surface area to volume ratio than larger blocks, resulting in more particles on the surface and more collisions per second, increasing the rate of the reaction
• One way to investigate the effect of surface area on the rate of reaction is by using a setup with marble chips reacting with hydrochloric acid to produce carbon dioxide gas
• Measuring the volume of a gas can be done using a gas syringe for more accurate results, or by measuring the mass of carbon dioxide gas lost on a balance
• Cotton-wool in the setup allows carbon dioxide gas to escape while preventing acid from splashing out of the flask, which could lead to inaccurate results