chemistry paper 2

• How do you measure the rate of a reaction?


  By measuring the quantity of a reactant used or the quantity of product formed over time
• What is the equation for calculating the mean rate of a reaction by measuring the amount of reactant used?

  Mean rate of reaction = quantity of reactant used/time taken
• What is the equation for calculating the mean rate of a reaction by measuring the amount of product formed?

  Mean rate of reaction = quantity of product formed/time takenSee an expert-written answer!We have an expert-written solution to this problem!
• What units can you measure the rate of a reaction in?

  g/s or cm3/s or mol/s
• How do you calculate the rate of a reaction at a specific time from graph of the quantity of reactant used or the quantity of product formed?

  By measuring the gradient of a tangent drawn at that specific time on the graph
• What are the five factors that can affect the rate of a reaction?

  Concentration of reactants in solution, pressure of reacting gases, surface area of solid reactants, temperature and the presence of a catalyst
• What theory can we use to explain how various factors affect the rate of a reaction?

  Collision theory
• What is collision theory?

  Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy
• What is the activation energy of a reaction?

  The minimum amount of energy that particles must have to react
• According to collision theory why does increasing concentration of reactant in solution increase the rate of the reaction?

  It increases the frequency of collisions and so increases the rate of reaction
• According to collision theory why does increasing the pressure of reacting gases increase the rate of the reaction?

  It increases the frequency of collisions and so increases the rate of reaction
• According to collision theory why does increasing the surface area of solid reactants in solution increase the rate of the reaction?

  It increases the frequency of collisions and so increases the rate of reaction
• According to collision theory why does increasing temperature increase the rate of the reaction?

  It increases the frequency of collisions and makes the collision more energetic and so increases the rate of reaction
• How do you increase the surface area of a solid reactant?

  Grind it into a powder that has smaller particle size
• What effect does increasing the temperature of a reaction by 10°C have on the rate of a reaction?

  It doubles it
• What is a catalyst?

  A chemical that changes the rate of a chemical reaction but is not used up in the reaction
• How do catalysts increase the rate of a reaction?

  By providing a different pathway for the reaction that has a lower activation energy
• How do you know in a reaction that a chemical is used in a reaction is a catalyst?

  It is not included in the chemical equation for the reaction
• What is a reversible reaction?


  Where the products of a chemical reaction can react to produce the original reactants
• What is the symbol used in reversible reaction equations that shows that the reaction is reversible?

  
• How can you change the direction of a reversible reaction?

  By changing the conditions; for example heating or cooling the reaction
• Describe the energy changes in a reversible reaction

  One direction will be exothermic and the other direction endothermic
• When is equilibrium in a reversible reaction achieved in apparatus which prevents the escape of reactants and products?

  When the rate of the forward and reverse reactions occur at exactly the same rate
• What affects the relative amount of all the reactants and products at equilibrium in a reversible reaction?

  The conditions
• What happens to an equilibrium if any of the conditions change?

  The system responds to counteract the change
• What does Le Chatelier's principle predict?

  The effects of changing conditions on a system at equilibrium
• What affect will changing the concentration of one of the reactants in a reversible reaction have on the equilibrium?

  The system will no longer be in equilibrium and the concentration of all the substances will change until equilibrium is reached again
• What happens when the concentration of a reactant is increased in a reversible reaction?

  More products will be formed until equilibrium is reached again
• What happens when the concentration of a product is decreased in a reversible reaction?

  More reactant will react until equilibrium is reached again
• What happens when the temperature of a system in equilibrium is increased?

  The relative amount of products at equilibrium increases for an endothermic reaction OR The relative amount of products at equilibrium decreases for an exothermic reaction
• What happens when the temperature of a system in equilibrium is decreased?

  The relative amount of products at equilibrium decreases for an endothermic reaction OR The relative amount of products at equilibrium increases for an exothermic reaction
• What happens in gaseous reactions when the pressure of a system in equilibrium is increased?

  The equilibrium position shifts towards the side with the smaller number of molecules as shown by the symbol equation for the reaction
• What happens in gaseous reactions when the pressure of a system in equilibrium is decreased?

  The equilibrium position shifts towards the side with the larger number of molecules as shown by the symbol equation for the reaction
• Where is crude oil found?

  In rocks
• What is crude oil formed from?

  The remains of an ancient biomass consisting mainly of plankton that was buried in mud
• What chemically is crude oil?

  A mixture of a large number of compounds; mainly hydrocarbons
• What is a hydrocarbon?

  A molecule made up of carbon and hydrogen only
• What type of hydrocarbons are most of those found in crude oil?

  Alkanes
• What is the general formula of alkanes?

  CnH2n + 2
• What are the first four members of the homologous series of alkanes called?

  Methane, ethane, propane and butane