Energetics Flashcards
What happens in exothermic reactions?
heat energy is given out to the surroundings
What happens in endothermic reactions?
heat energy is taken in from the surroundings
What is enthalpy change and the symbol used?
ΔH, change in heat energy at constant pressure
What is standard enthalpy change and the symbol used?
ΔH⦵, change in heat energy at 100kPa, and all substances in their standard states
What does standard state mean?
formula and state at 298K
What is standard enthalpy of formation and the symbol used?
ΔHf⦵, the enthalpy change when 1 mole of a substance is formed from it’s elements, at 100kPa with all substances in their standard states
What are you trying to do when writing an equation where the enthalpy change is the same as the standard enthalpy of formation?
the product should be 1 mole ALWAYS, NEED STATE SYMBOLS
What is standard enthalpy of combustion and the symbol used?
ΔHc⦵, the enthalpy change when 1 mole of a substance undergoes complete combustion in a plentiful supply of oxygen, at 100kPa, and all substances in their standard states
How do you write equations where the enthalpy change is equal to the standard enthalpy change of combustion?
do a normal balanced complete combustion equation, NEED STATE SYMBOLS
What is Hess’s Law?
enthalpy change is the same irrespective of the route taken
When calculating COMBUSTION, the arrows go…
upwards
When calculating FORMATION, the arrows go…
downwards, towards the ‘products of combustion’
What are the 3 ways of calculating energy change, most to least accurate?
enthalpy cycles, calorimetry, mean bond enthalpy calculations
What is bond dissociation enthalpy, and the symbol used?
ΔHB.D⦵, enthalpy change when 1 mole of a certain type of covalent bond is broken homolytically , with all species in the gaseous state
Breaking and making bonds respectively require…
breaking- endothermic, making- exothermic
