energy from fuels

• What is a fuel?

  A substance which burns to release energy
• Examples of fuels

  Ethanol, natural gas, petrol, sugar etc
• Which two elements are always present in a fuel?

  Carbon and hydrogen
• What forms of energy are released when a fuel burns?

  kinetic energy, sound energy, heat energy
• What is burning also known as?

  Combustion
• When a fuel burns what is it reacting with?

  Oxygen
• Examples of greenhouse gases

  Methane, carbon dioxide, nitrous oxide
• What are the gases involved in acid rain?

  Sulphur dioxide, nitrogen dioxide
• How do catalytic converters work?

  They use catalysts platinum (for the oxidation reaction) and rhodium (for the reduction reaction) to catalyse the conversion of harmful gases to harmless gases.

  
  

  They convert nitrogen oxides to nitrogen, unburnt hydrocarbons to carbon dioxide and water, and carbon monoxide to carbon dioxide
• Why are alcohols good fuels?

  - they burn with a clean, blue flame

  - they burn to release a significant amount of energy

  - some alcohols are renewable
• What is the equation for the complete combustion of a hydrocarbon?

  hydrocarbon + oxygen --> carbon dioxide + water
• What is the equation for the incomplete combustion of a hydrocarbon

  Hydrocarbon + oxygen —> carbon monoxide + water
• What is a disadvantage to carbon dioxide

  Carbon dioxide controbutes to global warming
• How do you balance the number of oxygen molecules in a balanced equation when there are an odd number of oxygen molecules?

  Divide the odd number by 2 and represent the number as (odd number/2) O2
• all combustion reactions are

  exothermic
• Equation for the energy released from a fuel?

  Eh = cm∆T
• Why might the results of a specific heat capacity experiment be not accurate?

  Heat is lost to the surroundings
• How can you improve the specific heat capacity experiment?

  Use a draught shield - as this prevents the heat from being lost to the surroundings
• endothermic reaction


  A reaction which heat energy is absorbed. The temperature of the reaction decreases
• exothermic reaction


  A reaction which releases heat energy. The temperature of the reaction increases.
• Potential energy diagram for an endothermic reaction

  In an endothermic reaction, the change in heat is positive as heat energy has been taken in, therefore the temperature of the reaction decreases.

  
  

  The reactants in an endothermic reaction have lesser potential energy than the products.

  
  

  The enthalpy change is positive.

  
• Potential energy diagram for an exothermic reaction


  In an exothermic reaction, the change in heat energy is negative as heat energy has been released, therefore the temperature of the reaction rises.

  
  

  The reactants in an exothermic reaction have a greater potential energy than the products.

  
  

  The enthalpy change is negative

  
• What is ΔH

  The change in potential (heat) energy (enthalpy change) when reactants are converted to products
• activation energy


  Energy needed to get a reaction started
• How do you find the activation energy in a potential energy diagram?

  Measure the change in heat from the potential energy from the reactants to the peak of the reaction.
• What can you give the reactants enough energy to react?

  A spark or a flame
• What controls the rate of reaction?

  The size of the activation energy
• If a reaction has a small activation energy...

  The reaction is a fast reaction
• If the reaction has a large activation energy...

  The reaction is a slow reaction