3.1.4 energetics Flashcards
define enthalpy change
heat energy change measured under conditions of constant pressure
define standard enthalpy change of reaction
the enthalpy change of a reaction ( per mole of limiting reactants) with all reactants and products in their standard state under standard conditions
define standard enthalpy of combustion
the enthalpy change when 1 mole of a substance undergoes complete combustion in excess oxygen with all substances in their standard states under standard conditions
define enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions
define standard enthalpy change of nuetralisation
The enthalpy change when 1 mole of water is formed from the reaction of an acid and base under standard conditions
what are the standard conditions?
100 kpa and 298k
what is the equation for enthalpy change?
q = mc^t
q = enthalpy change
m = mass of substance ( usually water ) in grams
c = specific heat capacity
^t = change in temperature
define hess’ law
the overall enthalpy change for a reaction is independent of the route taken
define mean bond enthalpy
the energy required to break a covalent bond in a molecule averaged over a range of compounds
explain why a data book value would differ from your actual value obtained for bond enthalpy?
mean bond enthalpies were used in our calculations which differ from actual bond enthalpies
why would the standard enthalpy of formation be zero for some compounds?
because they are already in their standard state and an element
what is meant by exothermic?
a reaction with a net release of energy to the surroundings
when using mean bond enthalpy data how do you calculate enthalpy change?
^H = (energy to break bonds) - (energy to make bonds)
define endothermic
a reaction with a net energy absorbed from the surroundings
