FACTORS AFFECTING THE RATE OF CHEMICAL REACTION

• Chemical reaction


  • Substances are chemically converted to different substances
  • Atoms and molecules are rearranged to produce new substances with new properties
• Chemical reactions occur at different rates
• Factors affecting the rate of chemical reactions

  • Nature of the reacting substances
  • Concentration of the reactants
  • Effect of temperature
  • Presence of a catalyst
• Nature of the reacting substances

  Each substance has a unique structure of ions, atoms, and molecules which affects its reactivity
• Increase in concentration of reactants


  Increases the rate of reaction
• Effect of temperature


  Increase in temperature increases the kinetic energy of reacting particles, leading to more frequent and more energetic collisions
• As temperature increases, the rate of a chemical reaction usually doubles or triples for every 10°C increase
• Catalyst


  A substance that increases the rate of a chemical reaction without being consumed or altered itself

  
• Catalysts work by providing an alternative pathway with lower activation energy for the reaction
• Chemical reactions are an integral part of technology, culture, and life itself
• Some chemical reactions can be harmful to the environment, such as the release of pollutants
• Collision theory


  Explains the effect of temperature on chemical reactions
• Temperature is directly proportional to kinetic energy


  An increase in temperature results in an increase in the kinetic energy of the reacting particles
• Effects of increased kinetic energy

  • Increases the speed of the reacting particles, causing a greater proportion of collisions to take place in a given time
  • More collisions will have enough energy to equal or exceed the activation energy
• Ripe fruits are placed inside a refrigerator


  Slows down the ripening process
• Meat is cooked faster by using a pressure cooker


  Due to the higher temperature inside the pressure cooker
• General pattern


  The rate of a chemical reaction increases as the temperature increases, usually doubling or tripling for every 10°C increase in temperature
• At any temperature, the particles of reacting substances possess characteristic average velocity and energy
• As the temperature increases

  The energy of the particles also increases, resulting in greater movements of the particles
• Increased particle movements


  Increases the number of collisions between particles, thus increasing the rate of reaction
• Activation energy


  The added energy required by the reacting substances to complete the reaction
• Catalyst


  A substance that enhances the rate of a chemical reaction without itself undergoing any chemical change

  
• Inhibitor


  A substance that decreases the rate of a chemical reaction
• Catalysts


  • They accelerate reactions by providing a shorter path to the products
  • Small quantities of catalysts are needed to produce large amounts of products
• A catalyst can be added to a reaction to increase the reaction rate without getting consumed in the process

  
• A catalyst typically speeds up a reaction by reducing the activation energy or changing the reaction mechanism
• Common types of catalysts

  • Enzymes
  • Acid-base catalysts
  • Heterogeneous (or surface) catalysts
• Before the reaction takes place

  1. The reactants possess energy

  2. Energy increases until energy is obtained (activation energy) for the reactants to change into new substances (transition state)

  3. The energy of the system will decrease by releasing some energy into the surroundings

  
• Surface area


  A measure of the total area that the surface of an object occupies

  
• Increasing the surface area of a substance

  Generally increases the rate of the chemical reaction
• When a solid is finely divided, more of its surface area is exposed, making the chemical reaction occur faster
• For a given mass of solid

  As the particle size decreases, surface area increases
• Increase in surface area

  Increases the collisions between reacting particles
• The rate of reaction of gaseous substances

  May rise as the temperature increases
• Increase in the pressure of gas

  Brings the reacting particles closer to each other, thus increasing the rate of collisions
• Pressure has no significant effect on the reaction rates of solids and liquids
• Chemical reactions always exist around us and within our bodies, occurring simultaneously without our notice
• Food spoilage


  Occurs from the action of bacteria or fungi (molds)
• Decreasing the temperature of food


  Slows down the activities of bacteria and molds, preventing or delaying decay or spoilage
• Adding chemicals


  Limits the activity of microorganisms, preventing or delaying food spoilage