C7

• What is a commonly used electrolyte in hydrogen-oxygen fuel cells?

  Phosphoric acid
• What is the overall reaction in a hydrogen-oxygen fuel cell?

  reaction

  
• What is an exothermic reaction?

  An exothermic reaction is a reaction that transfers energy to the surroundings, so the temperature of the surroundings increases
• What is the reaction at the cathode (positive electrode) in a hydrogen-oxygen fuel cell?


  
• What affects the voltage of an electrochemical cell?

  The reactivity of the electrolyte and electrodes affects the voltage of a cell
• Is bond forming endothermic or exothermic?

  Exothermic, because energy is released when new bonds are formed
• Outline the required steps for bond energy calculations

  1 - Firstly, find the energy required to break bonds of the reactants

  2 - Then, find the energy required to form the new bonds of the products

  3 - Then do 'energy required to break bonds - energy released by forming bonds' to find the overall energy change
• What is a fuel cell?

  An electrical cell supplied with fuel and oxygen, that uses energy from the reaction to produce electricity
• Do sports injury cold packs use exothermic or endothermic chemical reactions?

  Endothermic
• What is the formula for calculating the energy change of a reaction using bond energies?

  energy required to break bonds - energy released by forming bonds
• If a chemical reaction has a negative energy change, is it exothermic or endothermic?

  Exothermic - the products have less energy than the reactants, meaning energy has been released to the surroundings
• Is bond breaking endothermic or exothermic?

  Endothermic - energy is required to break bonds
• Is bond forming endo or exo?

  Exothermic - energy is released when new bonds are formed
• How do hydrogen-oxygen fuel cells work?

  1 - The electrolyte is usually an acid and the electrodes are often porous carbon with a catalyst.

  2 - Hydrogen goes in the negative anode and oxygen goes in the positive cathode (opposite to electrolysis).

  3 - Hydrogen loses electrons and forms H+ ions (oxidation) and these ions move to the cathode.

  4 - Oxygen gains electrons at the cathode and then reacts with H+ ions to make water (reduction).

  5 - The overall reaction is hydrogen plus oxygen makes water.
• What is the reaction at the cathode (positive electrode) in a hydrogen-oxygen fuel cell?


  4H+ + O2 + 4e- ---> 2H2O
• What is a fuel cell?

  An electrical cell supplied with fuel and oxygen, that uses energy from the reaction to produce electricity.
• What are the advantages of using fuel cells in cars?

  1 - Don't produce as many pollutants

  2 - Rechargeable (though there is a limit to how many times they can recharge).

  3 - Fuel cells store more energy than batteries

  4 - They are less polluting to dispose of

  5 - Batteries are more expensive than fuel cells

  6 - Fuel cells store more energy than batteries

  7 - Only require hydrogen and oxygen, which are abundant
• What is the overall reaction in a hydrogen-oxygen fuel cell?

  2H2 + O2 ----> 2H20
• What is the reaction at the anode (negative electrode) in the hydrogen-oxygen fuel cell?

  H2 ---> 2e- + 2H+
• What are the electrodes in fuel cells made from?

  Porous carbon
• What are the 3 disadvantages of using fuel cells in cars?

  1 - Hydrogen takes up a lot of space as it is a gas

  2 - Hydrogen is explosive when mixed with water so hard to store safely

  3 - Making hydrogen requires electricity (which is usually generated through burning fossil fuels)
• In a hydrogen fuel cell is the anode positive or negative?

  Negative
• In a hydrogen fuel cell is the cathode positive or negative?

  Positive
• What are the electrodes made out of in hydrogen fuel cells?

  They are made out of porous carbon, with a catalyst
• At the cathode does oxygen gain or lose electrons? Why?

  Oxygen gains electrons from the cathode and reacts with H+ ions from the electrolyte to make water. This is called reduction.
• What happens at the anode in a hydrogen-oxygen fuel cell?

  This is where oxidation takes place
• What is needed to run a fuel cell?

  A constant supply of hydrogen
• Diagram of a hydrogen fuel cell

  A) hydrogen in

  B) oxygen in

  C) electrolyte

  D) negative anode

  E) positive cathode

  
• Electrochemical cells use chemical reactions to produce electricity.

  A cell can be made by connecting two different electrodes with a wire, and placing them in contact with an electrolyte. An electrolyte is a liquid through which charged ions can flow. There will often be a voltmeter so that you can measure the voltage of the cell.
• Electrochemical cell

  A) electrolyte

  B) Electrodes - 2 different metals, conduct electricity

  
• Batteries are similar to cells, but consist of two or more cells connected together in series to provide a greater voltage.
• Batteries

  A) cell

  B) cell

  C) cell

  D) battery

  
• Factors that affect the voltage of a cell:

  1. The metals used for the two electrodes. The greater the difference in reactivity of the two metals, the greater the voltage will be.
  2. The type and concentration of the electrolyte used.
  3. The conditions, such as temperature.
• Rechargeable cells 


  Rechargeable cells and batteries can be recharged because the chemical reactions are reversed when an external electrical current is supplied. These are the batteries used in laptops and mobile phones.
• What are non rechargeable cells?

  In non-rechargeable cells and batteries the chemical reactions stop when one of the reactants has been used up. These are the batteries usually used in smoke alarms and tv remotes. Alkaline batteries are non-rechargeable.
• How is an electrochemical cell set up?

  See diagram

  A) Voltmeter - connected to electrodes with wire

  B) electrolyte - contains ions that react with electrodes

  C) Electrodes - 2 different metals, conduct electricity

  
• Why do non-rechargeable batteries run out?

  The chemical reactants are fully used up, so no more electricity can be produced.
• Are alkaline batteries rechargeable or non-rechargeable?

  Non-rechargeable
• How are rechargeable batteries recharged?

  The chemical reactions are reversed when an external electrical current is supplied.
• What is an electrochemical cell?

  An electrochemical cell is a device that can generate electrical energy from the chemical reactions occurring within it.

  It is formed from 2 electrodes in contact with each other via a wire and an electrolyte.