rates of reaction

• rate of reaction= amount of reactant used/time taken
• To draw tangents on the curve of a rate of reaction graph:

  • Understand how to draw a straight line that touches the curve at a specific point
  • This straight line is called a tangent
• The slope of the tangent can be used as a measure of the rate of reaction
• The slope of the graph of a rate of reaction indicates the speed of the reaction at different points in time
• Initially, the reaction is fast, then it slows down, and finally, it stops
• Scientists use tangents to overcome the problem of the changing slope of the curve, which makes it hard to determine the rate of reaction at specific points
• A tangent is a straight line that touches the curve at a specific point
• The slope of the tangent gives an indication of the rate of reaction at that point
• By drawing tangents at different points on the curve, scientists can analyze how the rate of reaction changes over time
• To calculate the rate of reaction using a tangent:

  • Construct a triangle using the tangent and the axes
  • Measure the vertical and horizontal sides of the triangle
  • Divide the vertical side by the horizontal side to find the rate of reaction
• In the example given, the rate of reaction at 30 seconds was calculated by dividing 14 grams (vertical side) by 25 seconds (horizontal side), resulting in a rate of 0.56 grams per second
• The rate of a chemical reaction can be found by measuring the

  quantity of a reactant used or the quantity of product formed over

  time:

  mean rate of reaction = quantity of reactant used

  time taken

  mean rate of reaction = quantity of product formed

  time taken

  The quantity of reactant or product can be measured by the mass in

  grams or by a volume in cm3.

  The units of rate of reaction may be given as g/s or cm3/s.
• Factors which affect the rates of chemical reactions include: the

  concentrations of reactants in solution, the pressure of reacting

  gases, the surface area of solid reactants, the temperature and the

  presence of catalysts
• Collision theory explains how various factors affect rates of

  reactions. According to this theory, chemical reactions can occur

  only when reacting particles collide with each other and with

  sufficient energy. The minimum amount of energy that particles

  must have to react is called the activation energy.
• Increasing the concentration of reactants in solution, the pressure of

  reacting gases, and the surface area of solid reactants increases

  the frequency of collisions and so increases the rate of reaction
• Increasing the temperature increases the frequency of collisions

  and makes the collisions more energetic, and so increases the rate

  of reaction
• Catalysts change the rate of chemical reactions but are not used up

  during the reaction. Different reactions need different catalysts.

  Enzymes act as catalysts in biological systems
• Catalysts increase the rate of reaction by providing a different

  pathway for the reaction that has a lower activation energy
• If a reversible reaction is exothermic in one direction, it is

  endothermic in the opposite direction. The same amount of energy

  is transferred in each case
• When a reversible reaction happens in apparatus where products and reactants cant escape, equilibrium is reached when the

  forward and reverse reactions occur at exactly the same rate
• If a system is at equilibrium and a change is made to any of the

  conditions, then the system responds to counteract the change. Le Chatelier's principle predicts what the change is
• If the concentration of one of the reactants or products is changed,

  the system is no longer at equilibrium and the concentrations of all

  the substances will change until equilibrium is reached again
• If the concentration of a reactant is increased, more products will be

  formed until equilibrium is reached again
• If concentration of a product is decreased, more reactants will

  react until equilibrium is reached again
• If the temp of a system at equilibrium is increased, endothermic products increase and vice versa
• Temp of a system at equilibrium being decreased, total products in an endothermic equation decrease and vice versa
• For gaseous reactions at equilibrium, increased pressure causes the equilibrium position move to the side with less molecules and vice versa
• what are the effects of increased pressure in a gaseous reaction

  Equilibrium to the side with less molecules