Enthalpy and entropy
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- Created on: 14-05-17 15:48
Enthalpy Change (delta H)
A measure of heat energy given out or taken in during a chemical reaction or physical change at constant pressure. (+ve/-ve)
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enthalpy change equation
q=mc(deltaT)
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Enthalpy of formation (f)
The enthalpy change when one mole of a substance is formed from its constituent element with all substances in their standard states. (mainly -ve)
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Enthalpy of combustion (c)
The enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in their standard state. (-ve)
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Enthalpy of neutralisation (neut)
The enthalpy change when one mole of water is produced in a reaction between an acid and an alkali under standard conditions. (-ve)
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First ionisation energy (1stIE)
The enthalpy change one mole mole of gaseous atoms loses one mole of electrons to produce one mole of gaseous singly positive ions (1+). (+ve)
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Second ionisation energy (2ndIE)
The enthalpy change when one mole of gaseous singly positive ions loses one mole of electrons to form gaseous doubly positive ions (2+). (+ve)
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First electron affinity (1st EA)
The enthalpy change when one mole of gaseous atoms gains one mole of electron to form one mole of gaseous singly negative ions (1-). (-ve)
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Second electron affinity (2ndEA)
The enthalpy change when one mole of gaseous singly negative ions gains one mole of electrons to form one mole of gaseous doubly negative ions (2-). (+ve)
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Enthalpy of atomisation (at)
The enthalpy change when one mole of gaseous atoms is produces from its constituent elements in its standard state. (+ve)
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Hydration enthalpy (hyd)
The enthalpy change when one mole of gaseous ions becomes hydrated (dissolves). (-ve)
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Enthalpy of solution (sol)
The enthalpy change when one mole of ionic solid dissolves in enough water so that the dissolved ions are well separated and do not interact with each other. (+ve/-ve)
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Bond dissociation enthalpy (dis)
The enthalpy change when one mole of covalent bonds are broken with al substances in the gaseous state. (+ve)
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Lattice enthalpy of formation (LEF)
The enthalpy change when one mole of solid ionic compound is formed from its constituent ions in the gaseous state. (-ve)
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Lattice enthalpy of dissociation (LED)
The enthalpy change when one mole of a solid ionic substance is broken down into its constituent ions in the gaseous state. (+ve)
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Enthalpy of vaporisation (vap)
The enthalpy change when one mole of a liquid is tuned into a gas. (+ve)
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Enthalpy of fusion (fus)
The enthalpy change when one mole of a solid is turned into a liquid. (+ve)
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Standard conditions
100 kPa and 298 K
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Mean bond enthalpy
The average value of the bond dissociation enthalpy for a given bond over a range of different compounds.
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Thermochemical cycle
a sequence of chemical reactions that convert a reactan into a prooduct. The total enthalpy change for the sequence is the same as the conversion of the reactants to the products directly, by any route.
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Measuring enthalpy change you need
1. mass of substance being heated/cooled 2.the temperature change 3. specific heat capacity of substance H2O= 4.2
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Hess's law
The enthalpy change for a reaction will be the same whatever route is taken from reactants to products.
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Enthalpy value of elements
in standard states =0
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Entropy (delta S)
A numerical measure of the disorder in a chemical system. (+ve/-ve)
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Gibbs free energy equation
deltaG = deltaH -T(deltaS)
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A reaction is spontaneous when...
delta G is negative (
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entropy of the reaction equation
(deltaS)total = (deltaS)system + (deltaS)surroundings, this is positive in spontaneous reactions
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(delta S)surroundings equation
(deltaS)surroundings = -(delta H)reaction / T(temperature inK)
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(deltaS) system equation
(delta S)system = total(deltaS) products - total(deltaS) reactants
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Other cards in this set
Card 2
Front
q=mc(deltaT)
Back
enthalpy change equation
Card 3
Front
The enthalpy change when one mole of a substance is formed from its constituent element with all substances in their standard states. (mainly -ve)
Back
Card 4
Front
The enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in their standard state. (-ve)
Back
Card 5
Front
The enthalpy change when one mole of water is produced in a reaction between an acid and an alkali under standard conditions. (-ve)
Back
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