topic 7 - exam qs

• What is this reaction?

  Exothermic

  
• Initial temperature of water is 19 degrees. Final temperature of water is 15 degrees. What do these temperature readings show about the type of heat change?

  It is endothermic because the reaction involves the absorption of heat from water therefore the decrease in temperature
• Reactions are accompanied by heat changes. The changes are the results of bonds being broken and formed. What are the heat energy changes that occur when bonds are broken and formed? 


  When bonds are broken heat energy is required, when bonds are formed heat energy is released
• Explain how the rate of reaction is altered by changing the size of the pieces of solid and by changing the temperature of the liquid:

  Smaller pieces of solid of the same mass have a larger surface area, causing more frequent collisions and a faster reaction rate. Higher temperature means particles move faster meaning more frequent collisions as they have more energy and more collisions have the required energy to react. This means there are more successful collisions and a faster rate of reaction.
• What would decrease the rate of reaction?

  Using a more dilute acid
• The rate of decomposition of hydrogen peroxide can be increased by adding a catalyst. How does the mass change of the catalyst change?

  The mass of the catalyst remains unchanged.
• Explain in terms of the energy involved in the breaking of bonds and in the making of bonds, why some reactions are exothermic.

  Energy is needed to break bonds and energy is released when bonds are formed. More heat is released forming bonds than needed to break bonds meaning the reaction is exothermic.
• What type of reaction is the reaction of zinc with copper sulphate?

  Redox - displacement
• What type of reaction is this?

  Endothermic

  
• What is a catalyst?

  A catalyst is a substance that speeds up the rate of reaction but is not used up in the reaction
• Explain why the rate of reaction increases when the concentration of one of the reactants is increased:

  There are more particles in the same volume and there are more collisions between particles in a given time therefore more frequent collisions.
• During any reaction, reactants are used up and the rate of reaction decreases. Explain, in terms of particles, why the rate of reaction decreases.


  As the reactants are used up, there are fewer particles to react and this will result in a lower frequency of collision so fewer particles react in a given time.
• Explain why it is not possible to predict what the rate of Experiment 2 will be compared with Experiment 1:

  The decrease in temperature will cause a decrease in the rate of reaction but the increase in pressure will cause an increase in the rate of reaction. Because the changes have opposite effects on the rate it is not possible to predict which has the greater effect.

  
• Explain in terms of breaking/forming bonds reactions are exothermic/endothermic:


  Breaking bonds requires heat, forming bonds releases heat. When more heat energy is given out than taken in, the reaction is exothermic. When more heat energy is taken in than given out, the reaction is endothermic.