Chemistry I
Chapter 11 Thermochemistry
Definitions
Thermochemistry: heat changes during chemical reactions
Energy: the capacity for doing work or supplying heat
Chemical Potential Energy: the energy stored within the structural units of
chemical substances….chemical bonds.
Heat (q): the energy that transfers from one object to another.
Note: Heat cannot be directly measured. Changes in temperature can be measured .
System: the part of the Universe that you focus your attention.
Surroundings: the rest of the universe surrounding
Universe: the system and its surroundings
The Law of the Conservation of Energy: in any chemical or physical
process, energy is neither lost nor made.
Endothermic: The system gains heat, the surroundings cool down
Exothermic: the system loses heat, the surroundings warm up
calorie: the quantity of heat needed to raise the temperature of 1 gram of
pure water 1 degree C.
NOTE: 1 Calorie = 1 kilocalorie = 1000 calories
Joule: the SI (international system) unit of heat and energy.
1 joule = 0.2390 calories
1 calorie = 4.184 joules
Specific heat capacity (a.k.a. Specific heat): amount of heat needed to
raise 1 gram of a substance 1 degree C.
Enthalpy: Heat changes for a reaction carried out at a constant pressure.
Δ H= q= Csp (J/g*C) * mass (gms) * Δ T (C◦)
If Δ H > 0 the reaction is Endothermic, If Δ H < 0 the reaction is Exothermic
Calorimetry: The accurate and precise measurement of heat change for a chemical
& physical process.
Calorimeter: the insulated device for the accurate and precise measurement of
heat changes for a chemical & physical process.
Thermochemical equation: An equation that includes the change in heat.
Heat of reaction: is the heat change for the equation exactly as it is written.
Heat of Combustion: The heat of the reaction for the complete burning of one
mole of a substance.
Molar heat of Fusion: (Δ Hfus) the amount of heat absorbed by one mole of a
substance as it melts form a solid to a liquid at a constant temperature.
Molar Heat of Solidification: (Δ Hsolid) the amount of heat released when one mole
of a liquid solidifies at a constant temperature.
Molar heat of vaporization: (Δ Hvap) the amount of heat necessary to vaporize one
mole of a liquid.
Molar heat of Condensation: (Δ Hcond) the amount of heat released when 1 mole of a
vapor condenses.
Molar heat of a Solution: (Δ Hsoln) the heat of change caused by the dissolution of
one mole of a substance.
Hess’s Law: or Hess’s law of heat summation, when adding two or more
thermochemical equations to get a final equation, you may also add the heats of
reaction to get the final heat of reaction.
Standard Heat of formation: (Δ Hfo) the change in enthalpy that accompanies the
formation of one mole of a compound from its elements with all their substances in
their standard state at 25 Co.