aqa gcse chemistry

• Why are alkenes unsaturated hydrocarbons?

  Because they contain two fewer hydrogen atoms that the alkane with the same number of carbon atoms
• What do saturated hydrocarbons only contain?

  Single bonds
• What is the general formula of an alkene?

  CnH2n
• What are alkenes?

  Hydrocarbons with a double carbon-carbon bond
• What are alkenes used for?

  To produce polymers and as starting materials to produce other chemicals
• Why are alkanes cracked?

  Because there is a high demand for fuels and some of the products of cracking are useful as fuels
• What can we use each fraction of crude oil for?

  As fuels or feedstocks for the petrochemical industry
• What does each fraction of crude oil contain?

  Molecules with a similar number of carbon atoms
• How can you separate crude oil into fractions?

  By fractional distillation
• What is a homologous series?

  A family of organic compounds that have the same functional group, similar chemical properties and the same general formula
• What are the first four members of the homologous series of alkanes called?

  Methane, ethane, propane and butane
• What is the general formula of alkanes?

  CnH2n + 2
• What type of hydrocarbons are most of those found in crude oil?

  Alkanes
• What is a hydrocarbon?

  A molecule made up of carbon and hydrogen only
• What chemically is crude oil?

  A mixture of a large number of compounds; mainly hydrocarbons
• What is crude oil formed from?

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

  In rocks
• 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
• 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 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 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 concentration of a product is decreased in a reversible reaction?

  More reactant will react 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 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 does Le Chatelier's principle predict?

  The effects of changing conditions on a system at equilibrium
• What happens to an equilibrium if any of the conditions change?

  The system responds to counteract the change
• What affects the relative amount of all the reactants and products at equilibrium in a reversible reaction?

  The conditions
• 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
• Describe the energy changes in a reversible reaction

  One direction will be exothermic and the other direction endothermic
• How can you change the direction of a reversible reaction?

  By changing the conditions; for example heating or cooling the reaction
• What is the symbol used in reversible reaction equations that shows that the reaction is reversible?

  
• What is a reversible reaction?

  Where the products of a chemical reaction can react to produce the original reactants
• 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
• How do catalysts increase the rate of a reaction?

  By providing a different pathway for the reaction that has a lower activation energy
• What is a catalyst?


  A chemical that changes the rate of a chemical reaction but is not used up in the reaction
• What effect does increasing the temperature of a reaction by 10°C have on the rate of a reaction?

  It doubles it
• How do you increase the surface area of a solid reactant?

  Grind it into a powder that has smaller particle size
• 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
• 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 the pressure of reacting gases increase the rate of the reaction?

  It increases the frequency of collisions and so increases the rate of reaction