ENTHALPY/ENTROPY DEFINITIONS AND RULES 0.0 / 5 ? ChemistryEnthalpyEntropyA2/A-levelOCR Created by: zahelCreated on: 09-10-16 17:16 Exothermic Making bonds - Energy given out (-ve enthalpy)energy lost in solution 1 of 25 Endothermic Breaking bonds - Energy taken in (+ve enthalpy) energy gained in solution 2 of 25 SEC of reaction Enthapy change when molar quantities shown in a chemical equation react in their given states, under standard conditions 3 of 25 SEC of formation Enthalpy change when one mole of a compound forms from its constituents in their standard states, under standard conditions 4 of 25 SEC of combustion Enthalpy change when one mole of s substances reacts completely with oxygen, under standard conditions 5 of 25 SEC of neutralisation Enthalpy change when and acid reacts with a base to form one mole of water, under standard conditions 6 of 25 SEC of atomisation Enthalpy change that takes place when one mole of gaseous atoms form from their element in its standard state, under standard conditions 7 of 25 1st ionisation energy Enthalpy change required to remove 1 mole of electrons from 1 mole of gaseous atoms under standard conditions to form one mole of gaseous 1+ ions 8 of 25 1st electron affinity Enthalpy change required to add 1 mole of electrons to 1 mole of gaseous atoms under standard conditions to form one mole of gaseous 1- ions 9 of 25 Lattice enthalpy Enthalpy change when 1 mole of crystal forms from its consituent ions in their gaseous state, under standard conditions 10 of 25 SEC of solution Enthalpy change to dissolve one mole of substance 11 of 25 SEC of hydration Enthalpy change required to form one mole of an ionic compound from its gaseos ions under standard conditions 12 of 25 Entropy Measure of dispersal of energy 13 of 25 Positive Entropy System has become more disordered (More favourable) 14 of 25 Negative Entropy System has become less disordered (Less favourable) 15 of 25 Calculating Free energy (DeltaG) DeltaH - (Temp K x DeltaSy) 16 of 25 Free energy feasibility Negative = Feasible 17 of 25 Calculating entropy of surroundings -DeltaH / Temp (in Kelvin) J k-1 Mol-1 18 of 25 Calculating entropy of system E(Products)-E(Reactants) 19 of 25 Calculating total entropy DeltaSsu + DeltaSsy 20 of 25 Entropy feasibility Positive DeltaT = Feasible 21 of 25 Total feasibilty Dependent on temperature, DeltaH and deltaS. 22 of 25 Increase charge effect on LE Greater attraction = More exothermic 23 of 25 Down a group effect on LE Increase ionic radius = decreased electron density = less attraction =less exothermic 24 of 25 Across a period effect on LE Ionic radius decrease = increased charge density = more attraction = more exothermic 25 of 25
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