Energetics: key definitions Flashcards
what is thermochemistry?
study of heat changes during chemical reactions
what is an exothermic reaction?
a reaction in which heat energy is released as reactants changed into products so the temperature rises
examples of exothermic reactions
- neutralising acid into alkali
- combustion of fuels
is the ∆H value negative or positive for an exothermic reaction?
negative - because loss of heat energy to surroundings
what is an endothermic reaction?
a reaction in which heat energy is absorbed as reactants changed into products so the temperature drops
examples of endothermic reactions
- breakdown of limestone
- heating copper sulfate
is the ∆H value negative or positive for an endothermic reaction?
positive - because products end up with more energy than reactants
what is enthalpy change?
heat energy change under constant pressure
what are standard conditions?
- 100 kPa
- 298K
what is the standard enthalpy of formation?
the enthalpy change when one mole of substance is formed from its constituent elements with all the reactants and products in standard states under standard conditions of 298K and 100 kPa
what is the standard enthalpy of combustion?
the enthalpy change when one mole of substance is completely burned in oxygen to form oxides with all the reactants and products in standard states under standard conditions of 298K and 100 kPa
what is standard enthalpy of neutralisation?
the enthalpy change when one mole of water is formed in a reaction between an acid and alkali under standard conditions of 100kPa and 298K.
formula for heat change, q, in a reaction
q=mc∆T
what is hess’ law?
the enthalpy change of a reaction is the same regardless of the route taken
what is bond enthalpy?
amount of energy required to break a particular bond
