energetics

• The enthalpy change is independent of the route taken
• What direction are the bottom arrows pointing in enthalpy of formation?

  Up
• What direction are the bottom arrows in enthalpy of combustion?

  Down
• How do you construct a hess cycle for formation?

  arrows upwards,constituent elements at bottom.If the new route goes against an arrow that value/values are negative.
• How do you construct a hess cycle for combustion?

  Arrows pointing down,carbon dioxide and h2o as the elements formed.If new route goes against the arrows the value becomes negative.
• Equation for formation

  
• Equation for combustion

  
• It doesn't matter what enthalpy change you are calculating only the data they've given you.
• What is the equation for enthalpy change?
• What is the equation for enthalpy change?

  Total enthalpy change=Bond broken-bonds formed.
• The standard state is defined as 1 atm pressure and 298 K temperature.
• Give two reasons why the enthalpy of combustion determined experimentally is less exothermic than that calculated using enthalpies of formation.

  -heat loss

  -incomplete combustion
• Explain why the value given for the O=O bond enthalpy in part (b) is not a mean value.

  oxygen is the only substance that has the o=o bond
• Suggest two disadvantages of using a glass beaker on a tripod and gauze

  -worser conductor than copper

  -both reduce heat transfer