3.1.4 Energetics Flashcards
first law of thermodynamics
energy cannot be created nor can it be destroyed it just
changes form
Enthalpy (H)
the heat energy that is stored in a chemical system (H)
Exothermic reactions
Reactions which give out heat as they proceed
Endothermic reactions
Reactions which take in heat from the surroundings to keep
going
Activation Energy
the minimum amount of energy which is required for a
reaction to start
Exothermic summary
^H is always negative, heat energy is given out to
surroundings, the reacting chemicals lose energy
Endothermic summary
^H is always positive, heat energy is always taken in from
the surroundings, the reacting chemicals gain energy
Enthalpy Change ^H
the heat energy change measured at a constant pressure
Specific heat capacity
the amount of heat needed to raise temperature of 1g of the
substance by 1’C
Standard Enthalpy of Formation ^Hf
the enthalpy change when one mole of a compound is
formed from its constituent elements under standard
conditions (all reactants and products being in their standard
states)
Standard Enthalpy of Combustion ^Hc
the enthalpy change when one mole of a substance is
completely burned in oxygen under standard conditions (all
reactants and products being in their standard states)
Hess’s Law
states that the overall enthalpy change for a reaction is
independent of route taken element’s have 0 enthalpy because they are element’s
Bond enthalpies
the energy needed to break one mole of chemical bonds in
molecules of a gaseous element or compound, such that the
resulting gaseous species exert no force on each other
Mean Bond Enthalpy
energy required to break a given covalent bond averaged
over a range of compounds
