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29 Cards in this Set
- Front
- Back
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What is enthalpy change? |
Heat change in a reaction under constant pressure |
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What is lattice formation enthalpy? |
Enthalpy change when 1 mole of a solid ionc lattice formed from its gaseous ions under standard conditions |
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What is the issue with lattice enthalpy? |
Can't be measured directly |
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What is enthalpy change of formation? |
Enthalpy change when 1 mole of a compound is formed from its consitituent elements under standard conditions reactants and products in standard states |
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What is bond dissociation enthalpy? |
Enthalpy change when all the bonds of the same type in one mole of gaseous molecules are broken to produce free radicals |
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What is the enthalpy of atomisation of an element? |
The enthalpy change when 1 mole of gaseous atoms are formed from an element in its standard state |
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What is the enthalpy of atomisation of a compound? |
Enthalpy change when 1 mnole of a compound in standard state separated into gaseous atoms |
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What is the 1st ionisation enthalpy? |
Enthalpy change when 1 mole of electrons removed from 1 mole of gaseous atoms to form one mole of gaseous 1+ ions |
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What is electron affinity? |
Enthalpy change when 1 mole of gaseous 1- ions formed from 1 mole of gaseous atoms |
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What is the enthalpy change of hydration? |
Enthalpy change when 1 mole of aqueous ions formed from 1 mole of gaseous ions under standard conditions |
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What is the enthalpy of solution?
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Enthalpy change when 1 mole of solute(ionic solid) is dissolved in sufficient solvent such that no further enthalpy change occurs on further dilution - ions are separated and do not interact |
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What is Hess' Law? |
Enthalpy change for a raction is the same independent of route by which reaction occurs |
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How can Born Haber cycles be used to predict if a compound exists? |
If enthalpy of formation is very endothermic unlikely to form as less stable |
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Explain why the second electron affinity has a large positive value. |
electron added to a negative ion so energy is required to overcome electrostatic repulsion |
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Explain why sodium forms a stable oxide of na+ and O2- ions byt not NaO or Na(1)O |
Na(2)O requires second ionisation of sodium, endothermic change enthalpy of formation less negative NaO less electrostatic attraction so enthalpy of formation less negative |
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Why is a compound insoluble? |
Hydration enthalpy is less than lattice dissociation enthalpy enthalpy of solution is positive |
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Why is the enthalpy of hydration negative? |
Attraction between polar water molecules and ions = formation of bonds |
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How can you measure bond dissociation enthalpy? |
spectroscopy |
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Why do mean bond enthlapy calculations give diff enthalpy values than experimental? |
Experimental more accurate/specific to compound mean taken as a average over range of compound bond enthalpy diff in each compopund due to diff environment |
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What is a spontaneous change? |
A reaction that will occur in one direction with no additional input of energy |
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What are the units of entropy? |
J/K/mol |
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What things affect the entropy of a molecule? |
Physical state How complicated |
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What is entropy? |
A measure of disorder of particles - number of ways they can be arranged and energy can be shared |
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Why can we define absolute standard entropies? |
All particles have 0 entropy at 0K No disorder/no movement |
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What are the units for free energy change? |
J/mol |
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What is free energy change? |
Predicts if a reaction is feasible. is feasible if less than or equal to 0 |
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Why does dissolving increase entropy? |
particles can move freely |
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Why do gases have a higher entropy? |
More disorder Particles move more rapidly and randomly and can be more randomly earranged |
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what can you say about the bonding character of rubidium chloride if lattice enthalpy change of formation is similar to that calculated using a Born Haber cycle? |
Little covalent character ions are sperical/point charges and no polarisation |
