paper 1 Flashcards
(35 cards)
enthalpy change
heat energy change at constant pressure
standard enthalpy of formation
enthalpy change when one mole of a substance is formed from its constituent elements under standard conditions, all reactants and products being in their standard states
standard enthalpy of combustion
enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions, all reactants and products being in their standard states
Hess’ law
enthalpy change for a chemical reaction is the same, whatever route is taken from reactants to products
mean bond enthalpy
enthalpy change when one mole of gaseous molecules each break a covalent bond, averaged over a range of compounds
activation energy (Ea)
minimum energy needed to start a reaction
1st ionisation energy
standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with one single positive charge
2nd ionisation energy
loss of a mole of electrons from a mole of singly positively charged ions
enthalpy of atomisation
enthalpy change which accompanies the formation of one mole of gaseous atoms from the element in its standard state under standard conditions
bond enthalpy
enthalpy change when one mole of gaseous molecules each breaks a covalent bond
1st electron affinity
standard enthalpy change when a mole of gaseous atoms is converted to a mole of gaseous ions, each with a single negative charge
2nd electron affinity
enthalpy change when a mole of electrons is added to a mole of gaseous ions each with a single negative charge to form ions each with two negative charges
lattice enthalpy of formation
standard enthalpy change when one mole of solid ionic compound is formed from its gaseous ions
lattice enthalpy of dissociation
standard enthalpy change when one mole of solid ionic compound dissociated into its gaseous ions
enthalpy of hydration
standard enthalpy change when water molecules surround one mole of gaseous ions
order of reaction
with respect to one of the species, is the power to which the concentration of that species is raised in the rate expression
overall order of reaction
the sum of the orders of reaction of all species in the rate expression, total order
rate constant (k)
a number that connects the concentration of reactants in a reaction to the rate of reaction
rate of reaction
the chance in concentration of any of the reactants or products within unit time
periodicity
repeating trends in element properties increasing atomic number
catalyst
a substance that increases the rate of a chemical reaction without being changed in chemical composition or amount
- work by providing an alternative pathway with a lower activation energy
- doesn’t affect position of equilibrium
greater entropy change -> more __ve ΔG will be -> reaction more favourable
negative
heterogeneous catalyst
in a different phase from the reactants
- can be poisoned by impurities that block the active sites and consequently have reduced efficiency
how V2O5 acts as a heterogeneous catalyst in the contact process
- V2O5 + SO2 -> SO3 + V2O4
- V2O4 +1/2 O2 -> V2O5
