enthalpy change Flashcards
(17 cards)
enthalpy change
heat energy change at constant pressure
first ionisation enthalpy
enthalpy change when one mole of electrons is removed from one mole of atoms with all substances in the gaseous state
define standard enthalpy change
enthalpy change measured under standard conditions of 100 kPa and 298K
standard enthalpy of reaction
enthalpy change when the amount of reactants shown in a balanced equation react to give products under standard conditions at 100kPa and 298K
define standard enthalpy of formation
-enthalpy change that occurs when 1 mole of a compound is formed from elements in their standard states
define enthalpy of combustion
-enthalpy change when 1 mole of a substance undergoes complete combustion (is completely burnt in oxygen) with all substances in their standard states
why is enthalpy of formation of an element = 0
standard enthalpy of formation for all elements in their standard states is ZERO BY DEFINITION
define activation energy
minimum energy required for a chemical reaction to occur
calorimetry
practical determination of enthalpy changes
q = mc🔺T
q = energy change (J)
m = mass of substance heated (H2O) (g)
c = specific heat capacity (JK-1g-1)
🔺T = temp change (K or °C)
Hess’s law
enthalpy change is independent of the route
using enthalpies of formation
both reactants and products are made from the same elements
using enthalpies of combustion
both the reactants and products will undergo combustion to form the same products
oxidation products
C > CO2
H > H2O
S > SO2
N > NO2
using enthalpies of combustion rules
arrows DOWN (from reactants and products down to oxidation products)
- equations balanced
- state symbols included
using enthalpies of formation rules
- arrows UP (from elements up to reactants and products)
- equations balanced
- state symbols included
second ionisation enthalpy
enthalpy change when one mole of electrons is removed from one mole of 1+ ions with all substances in a gaseous state
