5.1 Measuring energy changes

• Heat: a form of energy that is transferred from a warmer body to a cooler body

  • It has the ability to do work, when heat is transferred to an objects its particles gain in kinetic energy therefore increasing the temperature or a change in phase.
  • Kinetic energy is proportional to temperature
  • At absolute zero, all motion of particles stop and entropy is at a minimum
• System: all reactants, products, and any solvents

  Surroundings: everything external to the reacting substances, etc. apparatus that contains reactions, thermometers or other measuring devices, and the lab
• Chemical reaction: atoms of the reactants are rearranged to create new products, chemical bonds are broken (endothermic), new bonds are formed (exothermic)

  • Bond dissociation energy: the energy required to break a bond
• Change in enthalpy: the heat transferred by a closed system during a chemical reaction (ΔH)

  Units: kJ
• Calorimeter: A device used to measure the heat exchanged with the surroundings. If energy is released, the chemical reaction occurring is exothermic, if the energy is absorbed, the chemical reaction occurring is endothermic.
• q = mcΔT

  q = heat

  m = mass (kg)

  c = specific heat capacity (kJ/kgK)

  ΔT = (Tfinal - Tinitial)
• Specific heat capacity: the amount of heat needed to raise the temperature of 1g of a pure substance by 1°C
• Determining the change in temperature in calorimetry experiments

  A) Line of best fit

  
• To determine molar enthalpy change:

  q/molar mass
• Enthalpy of reaction (ΔHreaction) = Σ(ΔHf products) - Σ(ΔHf reactants)