rate and extent of chem change

• The steeper the line, the faster the rate of reaction

  
• The rate of chemical reaction depends on:

  • the collision frequency of reacting particles. More collisions means faster rate of reaction
  • energy transferred during collision - particles have to collide with enough energy
• Activation energy is the minimum amount of energy needed for a reaction to occur. Rate of reaction depends on:

  1. temperature
  2. concentration of solution or pressure of gas
  3. surface area
  4. presence of catalyst
• Increasing temperature


  When temperature is increases, particles move faster. If they move faster, they are likely to collide more frequently. The faster they move, the more energy they have - they will have enough energy to make the reaction happen.
• Increasing concentration or pressure

  If a solution is more concentrated, there are more particles in the same volume. Similarly, if pressure increases, there is the same number of particles in a smaller space. This increasing collision frequency.
• Increasing surface area


  If a reactant is a solid, breaking it up into smaller pieces increases its surface area to volume ratio. This means for the same volume, particles surrounding it have more area to work on, so collision frequency increases.
• Presence of catalyst



  A catalyst is a substance that speeds up a reaction without being used up. They work by decreasing the activation energy by providing an alternate reaction pathway with a lower activation energy.

  
• A reversible reaction is one in which the products can react to form the original reactants.
• As reactants react, their concentrations fall, so forward reaction slows down. But as more products are being made, their concentrations rise so the backward reaction speeds up.
• After a while, the forward reaction will be going at the same rate as the backward one, so the system is at equilibrium. This can only be reached in a closed system - no reactants or products can escape or enter.
• When a reaction is at equilibrium, it doesn't mean the amounts of reactants and products are equal. If it lies to the right, concentration of products is bigger than reactants. If it lies to the left, the concentration of reactants is bigger than products.
• Factors affecting position of equilibrium

  • temperature
  • pressure (only in gases)
  • concentration
• In reversible reactions, if the reaction is exothermic in one direction, it will be endothermic in the other - energy transferred from surroundings by endothermic reaction is equal to energy transferred to surroundings by exothermic reaction
• Le Chatelier's principle states that if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change.
• Temperature


  If you decrease the temperature, the equilibrium moves in the exothermic direction to produce more heat. If you increase the temperature, the equilibrium moves in the endothermic direction to cool it down.
• Pressure


  If you increase the pressure, the equilibrium moves in the direction where there are fewer molecules. If you decrease the pressure, it moves towards the side that has more molecules.
• Concentration


  If you increase concentration of reactants, the system makes more products. If you decrease the concentration of products, the system reduces the amount of reactants.