Energetics Flashcards
What is Hess’ law?
The enthalpy change for a chemical reaction is independent of the route taken to achieve that reaction, provided the initial and final conditions are the same
Define standard enthalpy change of reaction
Enthalpy change measured at standard conditions when the number of moles of the substances in the equation as written react
Define standard enthalpy change of formation
Enthalpy change measured at standard conditions when 1 mole of a substance is formed from its elements in their standard states
Define standard enthalpy change of combustion
Enthalpy change measured at standard conditions when 1 mole of a substance is completely burnt in oxygen
Define standard enthalpy change of neutralisation
Enthalpy change measured at standard conditions when 1 mole of water is formed from the neutralisation of an acid and an alkali
Define 1st ionisation energy
Energy required to remove 1 electron form each atom in 1 mole of gaseous atoms at standard conditions
What is the mean bond enthalpy?
Enthalpy change when 1 mole of gaseous molecules each breaks a covalent bond to form 2 free radicals, averaged over a range of compounds
Is bond breaking endothermic or exothermic?
Endothermic (takes in energy)
Is bond making endothermic or exothermic?
Exothermic (releases energy)
What is the equation for bond enthalpies?
Enthalpy change of reaction = sum of (bonds broken) +/-sum of (bonds made)
What is the enthalpy change and moles equation?
Q (J) = mc/\t
/\H = Q (kJ) / n
Q = heat change (J or kJ) m = mass (g) c = specific heat capacity (given) /\t = change in temperature (degrees C or kelvin) /\H = enthalpy change (kJ/mol) n = moles (mol)
What can be used to find the lattice enthalpy?
Born-Haber cycles
What determines polarising ability?
The smaller the atom and the higher the charge the more polarising it is.
(Charge density)
What is the equation for Gibb’s free energy?
/\G = /\H - T/\Ssystem
How do you find /\S?
/\S = (sum of Sproducts) - (sum of Sreactants)
