Energy changes

• What is an exothermic reaction?

  A reaction that causes a rise in temperature to surroundings- it releases energy
• What is an endothermic reaction?

  A reaction that causes a decrease in temperature in the surroundings-it takes in energy
• If a reversible reaction if exothermic in one direction what will it be in the reverse direction?

  Endothermic
• What must happen for bonds to be broken in a chemical reaction?

  Reacting particles must collide with sufficient energy
• What happens in a chemical reaction?

  Atoms are rearranged as old bonds are broken and new bonds are formed
• What is the activation energy?

  The minimum amount of energy that particles must have to take place
• What is the energy level diagram (reaction profile) for an exothermic reaction?

  
• Why does an exothermic reaction graph have that shape?

  Because energy is given out to the surroundings and the products have less energy than the reactants
• What is the energy level diagram (reaction profile) for an endothermic reaction?

  
• Why does an endothermic reaction graph has that shape?

  Because energy is taken in from the surroundings and the products have more energy than the surroundings
• Why do catalysts reduce the rate of reaction?

  It reduces the activation energy needed for a reaction

  
• Is breaking a bond in a chemical reaction an endothermic or exothermic process?

  Endothermic
• Is forming a bond in a chemical reaction an endothermic or exothermic process?

  Exothermic
• What determines if a reaction is exothermic?

  If the energy released when bonds are formed is greater than the energy needed to break bonds
• What determines if a reaction is endothermic?

  If the energy needed to break bonds is more than the energy released as bonds formed
• How can we measure the amount of energy produced in a chemical reaction in solution?

  By mixing the reactants in an insulated container. This enables heat that would be lost to surrounding to be measured.
• What sort of reactions is the insulated reaction method suitable for measuring energy produced?

  Neutralisation reactions and reaction involving solids
• How do cells (electricity) release energy?

  The chemicals inside react and release electricity
• How can a simple cell be made?

  By placing two different metals into a beaker containing an electrolyte
• What is a battery?

  2 or more cells connected together
• What happens in a hydrogen fuel cell?

  Hydrogen and oxygen are supplied to the cell. The fuel is oxidised to produce a potential difference, the hydrogen is oxidised to produce water
• In a hydrogen fuel cell, where is hydrogen added?

  At the anode
• What is the equation for hydrogen added at the anode in a fuel cell?

  2H2 = 4H+ + 4e-
• Where is oxygen added in a hydrogen fuel cell?

  At the cathode
• What happens at the cathode in a hydrogen fuel cell?

  The hydrogen atoms from the anode travel through the electrolyte to the cathode and react with the oxygen molecules at the cathode to form water.
• What is the equation for oxygen at the cathode in a hydrogen fuel cell?

  O2 + 4H+ = 2H2O
• What is the overall equation for what happens in a hydrogen fuel cell?

  2H2 + O2 = 2H2O
• Why are fuel cells becoming more popular than traditional methods of producing electricity?

  Traditional methods involve many stages and are less efficient and more polluting
• What are the advantages of hydrogen fuel cells?

  They produce water, which is not a pollutant, they are lightweight and small, they have no moving parts so are unlikely to break down
• What are the disadvantages of hydrogen fuel cell?

  Hydrogen gas has to be stored in pressurised containers and is explosive, most hydrogen gas is made by reacting steam with coal or natural gas, hydrogen can be made by electrolysis- using electricity produced with fossil fuels
• What are the disadvantages of being a consumer who uses hydrogen as a fuel?

  Not many filling stations sell hydrogen