Module 5: Enthalpoy And Entropy Flashcards by Shona Mallen

Definitions
What is enthalpy of formation

Enthalpy change when one mole of a substance is formed from its elements in their standard state

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What type of energy change is enthalpy of formation

Exothermic for most

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Equation for enthalpy of formation for sodium oxide

2Na(s) + 1/2 O2(g) —> Na2O(s)

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What is enthalpy of combustion

Enthalpy change when one mole of a substance undergoes complete combustion with all substances in their standard states

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What type of energy change is enthalpy of combustion

Exothermic

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What is the equation for combustion of ethane

C2H6 + 7/2 O2 —> 2 CO2 + 3 H2O

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What is enthalpy of neutralisation

Enthalpy change when one mole of water is formed in a reaction between an acid and alkali under standard conditions

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What energy change is enthalpy of neutralisation

Exothermic usually -57

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Equation for enthalpy of neutralisation for sulfuric acid and sodium hydroxide

1/2 H2SO4 (aq) + NaOH (aq) —> 1/2 H2SO4 (aq) + H2O (l)

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What is the first ionisation energy

Enthalpy Chang when one mole of gaseous atoms loses one mole of electrons to form one mole of gaseous 1- ions

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What type of reaction is first ionisation energy

Endothermic

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Equation for first ionisation energy of magnesium

Mg(g) —> Mg+ (g) + e-

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What is second ionisation energy

Enthalpy can change when one mole of gaseous 1+ ions loses one. Ole of electrons to form one mole of gaseous 2+ ions loses

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What energy change is second ionisationnnenegry

Endothermic

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Equation for second ionisation energy for magnesium

Mg+(g) —> Mg2+ (g) + e-

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What is the first electron affinity

Enthalpy change when one mole of gaseous atoms gains one mole of electrons to form one mol of 1- ions

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What type of energy change is first electron affinity

Exothermic for many non metals

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Equations for first electron affinity of oxygen

O(g) + e- —> O-(g)

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What is second electron affinity

Enthalpy Change when one mole of gaseosus 1– ions gains one mole of electrons to form one mole of gaseous 2- ions

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What type of energy change is second electron affinity and why

Endothermic as adding negative electrons to a negative ion so some repulsion

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Equation for second electron affinity of oxygen

O- (g) + e- —> O2- (g)

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What is enthalpy of atomisation

Enthalpy change when one mole of gaseous atoms is produced from an element in its standard state

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What type of energy change is enthalpy of atomisation

Endothermic

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Equation for enthalpy of atomisation of iodine

1/2 I2 (s) —> I (g)

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Definitions What is hydration enthalpy

Enthalpy change when one mole of gaseous ions dissolve in sufficient water to five an infinitely dilute solution

Definitions What type of energy b change is hydration enthalpy

Exothermic

Definitions Equation for hydration enthalpy of magnesium

Mg2+ (g) —> Mg2+ (aq)

Definitions What is enthalpy of solution

Enthalpy change when one mole of ionic substance dissolves in water to give an infinitely dilute solution

Definitions What type of energy change is enthalpy of solution

Varies

Definitions Equation for enthalpy og solution of magnesium chloride

MgCl2 (s) —> Mg2+ (aq) + 2 Cl- (aq)

Definitions What is bond dissociation enthalpy

Enthalpy changes when one mole of covalent bonds is broken in the gaseous state

Definitions What energy change is bond dissociation enthalpy

Endothermic

Definitions Equation for Bond dissociation enthalpy of I2

I2 (g) —> 2 I(g)

Definitions What is lattice enthalpy of formation

Enthalpy change when one mole of solid ionic lattic is formed from gaseous ions

Definitions When energy change is lattic enthalpy of formation

Exothermic

Definitions Equation for lattic enthalpy of formation for magnesium chloride

Mg2+ (g) + 2 Cl-(g) —> MgCl2 (s)

Definitions What is enthalpy of vaporisation

Enahtlpy change when one mole of a liquid is turned into a gas

Definitions What energy change is enthalpy og vaporisation

Endothermic

Definitions Equation for enthalpy of vaporisation of water

H2O (l) —> H2O(g)

Definitions What is enthalpy of fusion

Enthalpy change when one mole of a solid is tuned into a liquid

Definitions What energy change is enthalpy of fusion

Endothermic

Definitions Equation for enthalpy of fusion for magnesium

Mg (s) —> Mg(l)

Lattice enthalpy What is lattic enthalpy

Enthalpy change when one mole on a solid ionic compound is formed from its gaseous ions under standard conditions

Lattice enthalpy Equation for lattice enthalpy of potassium chloride

K+(g) + Cl-(g) —> KCl (s)

Lattice enthalpy What kind of energy change and why

Exothermic as involves formation of ionic bond

Lattice enthalpy What is lattic enthalpy also a measure of

Ionic bond strength

Lattice enthalpy What does a more negative lattic enthalpy value suggest

Stronger ionic bonding

Lattice enthalpy What is lattic enthalpy dependent upon

Charge density

Lattice enthalpy What two things is charge density dependent on

Ionic charge Size of ion

Lattice enthalpy What does a higher charge on the ion mean for lattic enthalpy

More energy is released when lattic formed due to stronger electrostatic forces between ions so more negative lattice enthalpy

Lattice enthalpy What does a smaller atomic radii of ions mean for lattic enthalpy;py

More exothermic as have higher charge density and ions can sit closer together in lattice

Lattice enthalpy Will LiCl or KCl have more negative lattice enthalpy

LiCl has more negative lattice enthalpy as higher charge density due to smaller ion

Lattice enthalpy Will MgCl2 or NaCl have a more negative lattic enthalpy and why

MgCl2 as higher charge so greater lattice strength due to greater charge density

Lattice enthalpy How can lattic enthalpy of a compound be found

Using a born haber cycle

Lattice enthalpy What is lattice enthalpy bvalue determined by born haber cycles named as and why

Experimental value as data used in cycle is determined by experiments

Born haber cycles for lattice enthalpy What is a born haber cycle

Cycles that includes all the enthalpy changes in the formation of the ionic compound

Born haber cycles for lattice enthalpy What is the lattic enthalpy shown as for this

Negative so equation can be written

Born haber cycles for lattice enthalpy What equation can be made from born haber

Enthalpy of formation of the ionic compound equals sum of all other enthalpy changes

Born haber cycles for lattice enthalpy What has to be drawn for each enthalpy change

A separate step

Born haber cycles for lattice enthalpy What does Hess law say

Total enthalpy change of reaction is always the same independent of whoich route taken

Born haber cycles for lattice enthalpy What is the route 1

Enthalpy of formation From elements in standard states down (exo) to solid ionic compound

Born haber cycles for lattice enthalpy What is route 2

From elements in standard state, atomisation of metal, atomisation of nonmetal, ionisation of metal, electron affinity of non metal, lattic enthalpy of formtionn

Born haber cycles for lattice enthalpy Describe arrow for atomisation enthalpy of metals

Arrow going from elements in standard states up (endo) to gaseous atom of metal and standard state non metal

Born haber cycles for lattice enthalpy Describe arrow for atomisation of non metal

From gaseous metal atom and standard state non metal going up (endo) to gaseous metal atom and gaseous non metal atom

Born haber cycles for lattice enthalpy Describe ionisation of metal

All ionisation energy endo so going up From gases of metal atom and ghaeosu non metal atom to gaseous metal ion and gaseous non metal atom and electron Do each ionisation energy in individual step n

Born haber cycles for lattice enthalpy Describe first electron affinity of non metal

Goes down as exothermic From gaseous metal ion and gaseaous non metal atom and electrons to gaseous metal ion and gaseous non metal 1- ion (and electron)

Born haber cycles for lattice enthalpy What is different about second electron affinity of non metal

Endothermic so arrow going upwards

Born haber cycles for lattice enthalpy Describes arrow for lattic enthalpy of the ionic product

Goes from gaseous ions of solid ionic product Arrow goes down as exothermic

Born haber cycles for lattice enthalpy What do need to be careful of when doing born haber

If need multiple species may have multiples of each enthalpy change

Solution and hydration What is enthalpy of solution

Enthalpy change when one mol of ionic substance dissolves in water to give a solution of infinite dilution

Solution and hydration Equation for enthalpy of solution for sodium chloride

NaCl(s) —> Na+ (aq) + Cl- (aq)

Solution and hydration What is the energy h age for enthalpy of solution

Can be either

Solution and hydration What is enthalpy of hydration

Enthalpy change when one mol of gaseous ions dissolves in sufficient water to give a infinitely dilute solution

Solution and hydration Equation for enthalpy of hydration for chlorine

Cl-(g) —> Cl-(aq)

Solution and hydration What is the energy change for enthalpy of hydration

Expothermic

Solution and hydration What can be constructed for these

Born haber cycles

Solution and hydration What goes at the top of these born haber cycles

Gaseous ions

Solution and hydration What always goies down from gaseous ions

Lattice enthalpy ands the hydration enthalpies of both species

Solution and hydration What can change about these cycles

Whether enthalpy of solution is endo or exo so can change position

Entropy What letter is given to entropy

Entropy What is it a measure of

Disorder

Entropy What is the term entropy used for

The dispersal of energy within the chemicals making up the chemical system

Entropy What does the greater the entropy ,mean

More disorder

Entropy What is the units

J K^-1 mol^-1

Entropy What state has the greatest entropy

Gas

Entropy What state has the lowest entropy

Solid

Entropy What two factors can affect change in entropy

Number of moles State

Entropy How do you explain increase in entropy due to change in state

Increase in entropy as particles are becoming more disordered

Entropy What happens to entropy as temperature increases

Entropy increases as faster particles move or vibrate so entropy increases

Entropy How can you predict the change in entropy from number of moles

If more moles on product side increase in entropy as have more moles of particles with disorder

Entropy What are standard entropy’s

Entropy of one mole of a substance under standard conditions

Entropy How do you calculate delta S

Sum of Sproducts - sum of Sreactants

Free energy What is feasibility

Term describes whether a reaction is able to happen and energetically feasible

Free energy What word may be used instead of feasibliklity

Spontaneous

Free energy What is the equation

/\G = /\H - T /\S

Free energy What is /\G and units

Gibbs free energy (overall change in energy during reaction) kJ mol^-1

Free energy What is /\ H and units

Enthalpy change with surroundings in kJ mol^-1

Free energy What is T sand units

Temperature in kelvin

Free energy What is /\S and units

Change in entropy in J K^-1 mol^-1

Free energy *** What is key in doing this equation

Convert /\S from J to kJ but divide by 1000

Free energy What has to be true for a reaction to be feasible

/\G <=0

Free energy What is a reaction being feasible dependent on

Temperature

Free energy How do you work out point at which reaction switches from being feasible to not

/\G=0 in equation using same /\H and /\S

Free energy Why may a reaction not be feasible

If has a very high Ea

Free energy H0w can this equation be applied to a graph

/\G on y axis T on x axis -/\S is gradient /\H is the y intercept