C6: Rate of Reaction

• Rates of reactions can be measured using the amount of product used, or amount of product formed over time: Rate of reaction = amount of reactant used /Time.
• The quantity of reactant or product can be measured by the mass in grams or by a volume in cm3.
• Units of rate of reaction may be given as g/s or cm3/s.
• The rate of reaction can also be calculated graphically by measuring the rate of reaction: draw tangents to curves and use the slope of the tangent.
• Factors which affect the rates of chemical reactions include concentration, pressure, surface area, temperature, and catalysts.
• Collision theory states that chemical reactions can occur only when reacting particles collide with each other and with sufficient energy.
• Activation energy is the minimum amount of energy that particles must have to react.
• Increasing the concentration of reactants in solution, the pressure of reacting gases, and the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction.
• Increasing the temperature increases the frequency of collisions and makes the collisions more energetic, and so increases the rate of reaction.
• Catalysts are substances that speed up chemical reactions without being changed or used up during the reaction.
• Enzymes act as biological catalysts.
• Catalysts are not included in the equation for a reaction.
• Catalysts decrease the activation energy; this increases the proportion of particles with energy to react.
• Catalysts provide a different pathway for a chemical reaction that has a lower activation energy.