enthalpy Flashcards
what are the standard conditions for enthalpy
pressure at 100KPa
temp of 298 K / 25 degrees
conc of 1 mol dm -3
define the standard enthalpy change of a reaction
the enthalpy change that accompanies a reaction under standard conditions when one mole of a substance is reacted
standard enthalpy change of combustion
when one mole of a substance completely reacts with oxygen under standard conditions with all reactants and products
define the standard enthalpy change of formation
enthalpy change when 1 mole of a substance is formed from its elements in their standard states under standard condition s
define the standard enthalpy change of hydration
enthalpy change when 1 mole of aqueous ions are formed from 1 mole of gaseous ions
name 2 factors that can affect the enthalpy change of hydration
the smaller the ion, the more exothermic the enthalpy change will be as due to the high charge density which increases the strong attraction between ions and water molecules
the higher the charge, the more exothermic the enthalpy - high charge density + stronger attraction
suggest what can make the enthalpy change of hydration more exothermic
decreasing ionic radius and increasing ionic charge
enthalpy change of neutralisation
enthalpy change when an acid and base reacts together to form one mole of liquid water under standard conditions
list 5 factors as to why there may be a difference between experimental and data book values
heat loss to surroundings
combustion of fuel was incomplete
fuel evaporated
water evaporated
conditions were non standard - alternative reaction so potentially other products were made
how can you reduce heat loss during experiment
lid over the top of calorimeter
using a draught shield
define hess cycle
enthalpy change is independent of the route take as long as the start and final conditions are the same
route 1 = route 2
when would the hess cycle be used
when the standard enthalpy change cannot be measured
