Rates and Equilibrium

• Calculating rates of reaction:

  Rate of a chemical reaction can be found by measuring the quantity of product formed over time:

  Mean rate of reaction = $\frac{quantity\ of\ reac\tan t\ used\ }{time\ taken\ }$

  Mean rate of reaction = $\frac{quantity\ of\ product\ formed}{time\ taken\ }$

  • Can be measured by the mass in grams or volume in cm$^3$.
  • Units given as g/s or cm$^3$/s.
• Factors which affect the rates of reactions:

  • The concentrations of reactants in the solution
  • Pressure of reacting gasses
  • Surface area of solid reactants
  • Temperature and presence of catalysts.
• Collision theory and activation energy:

  • How various factors affect rates of reactions. Chemical reactions can occur only when particles collide with each other and with sufficient energy. Minimum amount of energy which particles must have to react is activation energy.
  • Increasing the concentration of reactants, pressure of gasses, surface area increase the frequency of collisions and rate of reaction.
  • Increasing the temperature increases the frequency of collisions and makes the collisions more energetic.
• Catalysts:

  Catalysts change the rate of chemical reactions but are not used up during the reaction. Different reactions need different catalysts.

  • Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.