c5 questions

• in an exothermic reaction is heat transferred to or from the surroundings?

  To surroundings
• name two different types of reaction which are exothermic?

  Combustion, Neutralization
• define what is meant by an endothermic reaction?

  Absorbs heat , takes in energy ,
• define what is meant by an endothermic reactions?

  Absorbs heat , takes in energy , falls in temperature , ---

  some endothermic reactions also have everyday uses such as sport injury packs - the chemical reaction allows the pack to become instantlly cooler
• write down the equation for the thermal decomposition of calcium carbonate

  CaCO3 (+ HEAT) -> CO2 + CaO
• what is the purpose of putting the reaction container into a beaker containing cotton wool during an experiment to investigate the temperature change of an exothermic reaction?

  Insulation , to reduce heat loss
• what is the activation energy of a reaction?

  The minimum energy required for a reaction to occur.
• is the following true or false?

  in a endothermic reaction the products of the reaction have more energy then the reactants - true
• bond breaking is an endothermic process
• bond forming is an exothermic process
• in an endothermic reaction, the energy released by forming bonds is greater then then the energy used to break them
• what three steps would you use to find overall energy change in a reaction if you were given the known bonds present in the reactants and product?

  find the energy required to break the original bonds

  find the energy released by forming the new bonds

  find the overall energy change for the reaction
• what is an electrochemical cell?

  a basic system made up of two different electrodes In contact with an electrolyte
• give 2 factors that affect the voltage produced by an electrochemical cell?

   the types of electrode and electrolyte present.
• what is a battery?

   a battery is a collection of cells that provide a steady source of electrical energy. A battery provides a higher voltage and more energy than a single cell.
• explain why non-rechargeable batteries eventually lose their charge??

  .The chemical reactions are irreversible

  .The reactants get used up over time

  .Once any one of the reactants is used up, the reaction can't happen and no more electricity is produced

  . The products can't be turned back into the reactants, so the cell can't be recharged
• what is a.fuel cell?

  a electrical cell that's supplied with fuel and oxygen and uses energy from the reactions between them to produce electrical energy efficiently
• name an electrolyte commonly used in hydrogen-oxygen fuel cells?

  potassium hydroxide
• In a hydrogen-oxygen fuel cell, which molecule becomes oxidised and which becomes reduced?

  Oxygen becomes reduced, hydrogen becomes oxidized.
• write down the overall equation that takes place in a hydrogen-oxygen fuel cell described as a redox reaction?

  Hydrogen + Oxygen -> Water

  2H2 + 02 -> 2H20
• state 3 advantages of hydrogen-oxygen fuel cell powered cars over battery-powered electrical cars?

  Efficiency Faster refueling Longer range