C6

• Plotting the quantity of product formed against time gives a graph where the slope indicates the rate of reaction

  • The steeper the slope, the faster the reaction
  • Initially, the reaction is fast as a large number of reactant molecules are forming the product
  • As the reaction progresses, the slope becomes less steep, indicating a slower rate of reaction
  • When the slope is zero, the reaction has stopped because all the reactant molecules have reacted
• If the product is a gas, the quantity is measured in centimeters cubed
• To calculate the mean rate of reaction:

  • Mean rate of reaction = Quantity of product formed / Time taken
  • Example: 60 grams of product formed in 15 seconds gives a mean rate of reaction of 4 grams per second
• Calculating mean rate of reaction from the quantity of reactant used:

  • Mean rate of reaction = Quantity of reactant used / Time taken
  • Example: 30 grams of reactant used in 10 seconds gives a mean rate of reaction of 3 grams per second
• To measure the rate of reaction, draw tangents on the curve of the rate of reaction graph
• The slope of the tangent can be used as a measure of the rate of reaction
• To calculate the rate of reaction using the tangent:

  • Find the vertical side of the triangle by subtracting the y-values
  • Find the horizontal side of the triangle by subtracting the x-values
  • Divide the vertical side by the horizontal side to get the rate of reaction
• Collision Theory states that chemical reactions can only occur when reacting particles collide with each other and have sufficient energy
• The rate of a chemical reaction is determined by the frequency of successful collisions, which refers to the number of successful collisions per second
• Reactions are rapid initially due to a large number of reactant molecules, leading to a high number of collisions per second
• Over time, reactions slow down as the number of reactant molecules decreases, resulting in fewer collisions per second
• Finally, the reaction stops when all reactant molecules are depleted, causing the number of collisions per second to be zero
• The rate of reaction is proportional to the concentration of reactants, meaning that increasing the concentration increases the rate of reaction
• In a gas, increasing the pressure also increases the rate of reaction, following the same principle as concentration
• Higher concentration or pressure leads to a faster reaction and a steeper line on a graph of quantity of product over time
• Higher concentration results in more product at the end of the reaction due to starting with more reactant molecules
• Reversible reactions

  1. Can react in both forward and backward directions

  2. One direction is exothermic and the other endothermic
• Equilibrium

  When the forward and backward reactions are happening at the same rate, concentrations of reactants and products remain constant
• Equilibrium


  • Both reactions are still happening but effectively cancel each other out, no overall change in concentrations
• Position of equilibrium

  • Can change depending on conditions
  • Shifts to the left or right
• Adding heat to a reaction

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

  Pushes the equilibrium back to the left
• Equilibrium can only be reached in a closed system where none of the reactants or products can escape
• Thermal decomposition of hydrated copper sulfate

  • Forward reaction is endothermic, backward reaction is exothermic
• Hydrated means water is present, anhydrous means there's no water
• Thermal decomposition of hydrated copper sulfate

  Forward reaction requires heat energy, backward reaction releases energy
• le chatelier's principle


  Le Chatelier's principle states that if you change the conditions of a reversible reaction, the position of equilibrium will shift to try and counteract the change
• if pressure is increased, equilibrium will shift to decrease the pressure. This means that equilibrium will shift to the side will less moles of gas as these will contribute less pressure
• Shift the position of equilibrium to the right if pressure is increased

  N2(g) + 3H2(g) ⇋ 2NH3(g)
• If you increase the temperature, the position of equilibrium will shift to reduce the temperature. This means equilibrium will shift in the endothermic direction
• if you increase the concentration of a substance, the position of equilibrium will shift to reduce the concentration back down. This means that if you increase the concentration of nitrogen, equilibrium will shift to the right so that the concentration of nitrogen decreases again.

  N2(g) + 3H2(g) ⇋ 2NH3(g)
• Le Chatelier's Principle

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

  Refers to the ratio of reactant particles to product particles at equilibrium
• Le Chatelier's Principle

  If conditions of a reversible reaction are changed, the position of equilibrium will shift to counteract that change
• Example reaction

  • Production of ammonia from nitrogen and hydrogen
• Decreasing temperature

  Equilibrium moves in the exothermic direction to release heat energy
• Increasing temperature

  Equilibrium moves in the endothermic direction to absorb heat energy, shifting to the opposite side
• Increasing pressure


  Equilibrium moves to the side with fewer molecules to reduce pressure
• Decreasing pressure


  Equilibrium moves to the side with more molecules to increase pressure
• Adding more nitrogen


  Equilibrium shifts to the side with fewer nitrogen molecules, forming more ammonia, shifting to the right