chem 2

• Rate of chemical reaction

  The speed with which the reactants get turned into products
• Measuring the rate of reaction


  1. Measure how fast the reactants are being used up

  2. Measure how fast the products are being formed
• Rate of reaction = quantity of reactants used / time taken
• Rate of reaction = quantity of products formed / time taken
• Slow reaction


  • Rusting of iron (years or decades)
• Typical reaction


  • Reaction between magnesium and acid (gentle stream of hydrogen bubbles)
• Fast reaction


  • Explosions like fireworks (fraction of a second)
• The rate of reaction starts off fast when there are lots of reactants, then slows down as the reaction progresses and the reactants get used up
• Plotting graphs to show rate of reaction

  1. Time on x-axis

  2. Mass of reactants remaining or volume of product produced on y-axis
• The graph of mass of reactants remaining starts high and decreases rapidly at first, then slows down as the reaction progresses
• The graph of volume of product produced starts at zero, then increases rapidly at first, then slows down as the reaction progresses
• Units for rate of reaction

  Grams/seconds, centimetres cubed/seconds, moles/minutes, decimetres cubed/seconds
• The units used for the rate of reaction depend on what is being measured (reactants or products) and the time period
• Reversible reaction


  A reaction with a double arrow in the middle, indicating it can react in both forward and backward directions
• Reversible reaction


  1. Forward reaction

  2. Backward reaction
• Equilibrium


  The point where the forward and backward reactions are occurring at the same rate, so there is no overall change in concentrations
• Position of equilibrium


  The relative concentrations of reactants and products at equilibrium, which can shift left or right depending on conditions
• Adding heat to the reaction

  Encourages the forward reaction, shifting the position of equilibrium to the right
• Cooling the reaction


  Pushes the position of equilibrium back to the left
• Reversible reactions can only reach equilibrium in a closed system</b>
• Exothermic


  A reaction that releases heat energy
• Endothermic


  A reaction that absorbs heat energy
• Reversible reactions are always exothermic in one direction and endothermic in the other
• Hydrated


  Containing water
• Anhydrous


  Containing no water
• Thermal decomposition of hydrated copper sulfate

  1. Heating drives the forward endothermic reaction, producing anhydrous copper sulfate

  2. Adding water drives the backward exothermic reaction, reforming the hydrated copper sulfate
• Le Chatelier's Principle


  Principle about the position of equilibrium during a reversible reaction and how it's affected by temperature, pressure, and concentration
• Position of equilibrium


  Ratio of reactant particles to product particles when at equilibrium
• If you change the conditions of a reversible reaction

  The position of equilibrium will shift to try and counteract that change
• Production of ammonia from nitrogen and hydrogen

  1. Decrease temperature

  2. Increase temperature

  3. Increase pressure

  4. Decrease pressure

  5. Increase nitrogen concentration
• Energy change of forward reaction

  • 92 kilojoules per mole, exothermic
• Decrease temperature


  Equilibrium moves in exothermic direction (to the right)
• Increase temperature


  Equilibrium moves in endothermic direction (to the left)
• Increase pressure


  Equilibrium moves to side with fewer molecules (to the right)
• Decrease pressure


  Equilibrium moves to side with more molecules (to the left)
• Increase nitrogen concentration


  Equilibrium shifts to opposite side (to the right, forming more ammonia)
• Organic chemistry


  Chemistry of compounds containing carbon
• Carbon


  • Useful for making large compounds
  • Can form four strong bonds
  • Most commonly bonded to other carbon atoms or hydrogen atoms
• Hydrocarbons


  Compounds formed from carbon and hydrogen only
• Hydrocarbons


  • Butane
  • Butanol (not a hydrocarbon as it contains oxygen)