Rates of Reaction and Equilibrium

• How can you measure rates of reaction?

  Can be measured either by how fast a reactant is used up or how fast the product is made
• Formula to calculate rate of reaction


  Reactant used or product formed/time taken
• How to measure rate of reaction by loss in mass

  If one of the products is gas which is given off, then the reaction can be performed in an open flask on a balance ot measure the loss of mass of reactant
• Diagram showing the set-up for measuring the rate of reaction by loss in mass

  
• Why do you use cotton wool?

  Usually placed in the mouth of the flask which allows gas out but prevents any material from being ejected from the flaks (if reaction is vigorous)
• Why is this method not suitable for gases?

  The loss in mass may be too small to measure so a gas syringe which measures its volume
• Diagram of gas syringe used to determine rate of reaction

  
• Method to show rate of precipitation

  
• Why does the cross disappear?

  Because a solid precipitate forms when two clear solutions are mixed together - precipitate clouds the reaction mixture so if the flask is placed over a piece of paper with cross on it
• What happens in a graph where the factor being measured and the amount produced is directly proportional?

  Results the graph being a straight line graph going through the origin
• What happens to the rate of reaction when the gradient is steeper?

  The faster the rate of reaction
• What happens when the line becomes less steep and eventually horizontal?

  The reaction has finished
• What happens to the graph when the concentration is half or double

  
• When do you need to use a tangent to find the rate of reaction on a graph?

  For a curve graph
• How to find the gradient of the a point on a curve graph?


  Difference in Y divided by difference in X
• What are the factors that affect rate of reaction?

  -Conc of reactants in solution or the pressure of reacting gases

  -Temperature at which the reaction is carried out

  -Surface area of solid reactants

  -Use of a catalyst
• Required practical: Investigating Effect of concentration on rate of reaction diagram

  
• Method for this practical

  1.Measure 50cm3 of Na2S2O3 solution into a flask

  2.Measure 5cm3 of dilute HCI into a measuring cylinder

  3.Draw a dark cross on a piece of white paper and put it underneath the flask

  4.Add the acid into the flask and immediately start the stopwatch

  5.Solid sulphur is formed which precipitates in solution, turning cloudy

  6.Look down at the cross and stop the timing when the cross can no longer be seen

  7.Repeat using different concentrations of sodium thiosulfate solution
• What does the collision theory state?


  That chemicals reactions occur when the reactant particles collide with sufficient energy to react
• What is minimum amount of energy needed for a chemical reaction called?

  activation energy
• What happens to particle that collide with each other with insufficient energy?

  They have unsuccessful collision and just bounced off each other
• What does the rate of reaction depend on?

  On the energy of collision as well as the number of collision
• How would you increase the rate of reaction?

  Increase the number of successful collision
• What factors increase the rate of reaction?

  -Increasing concentration

  -Increasing temperature

  -Increase the surface area

  -Use of a catalyst
• How does increasing the concentration of a solution increase the rate of reaction?

  More reactant particles in a given volume, allowing more frequent and successful collision per second, increasing the rate of reaction
• How does increasing the temperature increase the rate of reaction?


  The particles will have more kinetic energy than the required activation energy, therefore there will be more frequent collisions and a higher proportion of particles have energy greater than the activation energy. This causes more successful collisions per second increasing the rate of reaction
• How does increasing the surface area increase the rate of reaction?

  More surface area of particles will be exposed to the other reactant, producing a higher number of collisions per second so increase the rate of reaction
• What are catalyst?

  Substance which speed up the rate of a reaction without themselves being altered or consumed in the reaction - the mass of a catalyst at the beginning and end of a reaction is the same as the
• How does a catalyst increase the rate of a reaction?

  Provides an alternative reaction pathway with a lower activation energy so increases the rate
• A reaction profile showing the effect of using a catalyst on the activation energy of a reaction

  
• What's a dynamic equilibrium?

  Forward reaction is happening at the same time and rate as the backward reactions
• What is a characteristic of dynamic equilibrium?

  1) The rate of the forward reaction is equal to the rate of the backwards reaction

  2) The concentration of the reactants and the products remain constant
• What can a dynamic equilibrium only happen in?

  A closed system
• What's a closed system

  Where reactants and products can't escape
• What happens if the conditions of the equilibrium change?

  The position of the equilibrium can move slightly to the left hand side or the right hand side to counteract the change
• What are the conditions that can affect the equilibrium position?

  Temp, concentration, pressure and catalyst
• What is concentration?


  The number of solute particles in a given volume of solution
• Why does the equilibrium always to shift to do?

  Oppose the change
• What happens to the equilibrium position if you increase the concentration?

  Increasing the concentration - this increases the number of particles in a given volume - therefore the position of the equilibrium will shift to the side with the lowest concentration to increase that sides concentration
• Example of this