calorimetry

• Sources errors in calorimetry

  • heat lost to surroundings
  • possible incomplete combustion
  • loss of some reactant as it evaporates before it combusts
• Why are the initial and final temperatures in a calorimeter inaccurate?

  Heat is always being lost from the calorimeter
• what are standard conditions?

  -pressure of 100kPa

  -temperature of 298K
• what are the standard enthalpy changes?

  -standard enthalpy of combustion

  -standard enthalpy of formation
• standard enthalpy change of combustion:

  -the enthalpy change when one mole of a substance in its standard state burns completely in oxygen under standard conditions
• what is the formula for energy change?


  q= mass*specific heat capacity*temperature change
• formula for enthalpy change per mole:

  q/moles
• what is Hess’s law?

  energy in a reaction system must be conserved, as it cannot be created or destroyed. Therefore the overall enthalpy change for a reaction is the same, regardless of the route taken.
• in enthalpy of formation, the arrows always point out from the central products
• in enthalpy of combustion, the arrows point towards the central products (which is always H2O and CO2).
• state Hess’s Law

  the enthalpy change for a reaction is independent on the route
• define the term standard molar enthalpy of formation (3 marks)

  enthalpy change when 1 mol of a compound is formed from its constituent elements in their standard states