5.6 rate and extent of chemical change

• rate of reaction = amount of reactant used / time OR amount of product formed / time
• rate of reaction is measured in g/s or cm^3/s
• factors which affect the rates of chemical reactions

  concentration, pressure, surface area, temperature , catalysts
• collision theory = chemical reactions can occur only when reacting particles collide with each other with enough energy
• increasing concentration of reactants in a solution increases the frequency of collisions and increases the rate of reaction
• increasing the pressure of reacting gases increases the frequency of collisions and increases the rate of reaction
• increasing the surface area of solid reactants increases the frequency of collisions and increases the rate of reaction
• increasing the temperature increases the frequency of collisions and gives the particles more energy, so it increases the rate of reaction
• catalysts are substances that speed up a chemical reaction without being used up in the reaction
• catalysts are not included in the equation for a reaction
• catalysts decrease the activation energy, which increases the proportion of particles with enough energy to react
• catalysts provide a different pathway for the reaction with a lower activation energy
• the haber process 


  hydrogen + nitrogen >< ammonia
• the direction of reversible reactions can be changed by changing the conditions.
• if a reversible reaction is endothermic one way, it is exothermic in the opposite direction
• the same amount of energy is transferred each direction in a chemical reaction, one way it is lost and the other it is gained
• when a reversible reaction occurs in a closed system, equilibrium is reached when the forward and reverse reactions are equal
• concentration of reactants increases


  equilibrium shifts towards products, more product is formed
• concentration of products increases 


  equilibrium shifts towards reactants, more reactants formed
• temperature increases

  equilibrium shifts in the direction of the endothermic reaction
• temperature decreases


  equilibrium shifts in the direction of the exothermic reaction
• if pressure is increased

  equilibrium shifts to side of reaction with fewer moles of gas
• if pressure is decreased

  equilibrium shifts to side of reaction with fewer moles of gas