Chapter 17 - Thermodynamics

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33 Terms

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enthalpy of formation definition

the enthalpy change when 1 mol of a compound is formed from its constituent elements under standard conditions. All reactants and products in standard states

2
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enthalpy of combustion definition

the enthalpy change when 1 mol of a substance completely burns under oxygen under standard conditions. All reactants and products in standard states

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enthalpy of reaction definition

the enthalpy change when a reaction occurs in the molar quantities shown in the chemical equation. All reactants and products in standard states

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enthalpy change of neutralisation

the enthalpy change when an alkali and acid react to form 1 mol of water under standard conditions

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Enthalpy definition

the heat energy change of a substance under constant pressure

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the enthalpy of atomisation

the enthalpy change when 1 mol of gaseous atoms is formed from its constituent elements under standard conditions

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first ionisation energy

the energy required to form 1 mol of gaseous unipositive ions from 1 mol of gaseous atoms under standard conditions

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second ionisation energy

the energy required to form 1 mol of gaseous dipositive ions from 1 mol of gaseous unipositive ions

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first electron affinity

the enthalpy change when 1 mol of gaseous atoms each gain an electron to form 1 mol of gaseous uninegative ions under standard conditions

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second electron affinity

the enthalpy change when 1 mol of gaseous uninegative ions each gain an electron to form 1 mol of gaseous dinegative ions under standard conditions

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enthalpy change of solution

the enthalpy change when 1 mol of a solute dissolved by a solvent under standard conditions

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enthalpy change of hydration

the enthalpy change when 1 mol of gaseous ions dissolved in water to form 1 mol of hydrated ions

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enthalpy of lattice formation

the enthalpy change when 1 mol of a solid ionic compound formed from its constituent ions in the gaseous phase under standard conditions

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enthalpy of lattice dissociation

the enthalpy change when 1 mol of a solid ionic compound broken down to its constituent ions in the ions in gaseous phase under standard conditions

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why does magnesium ion have a greater hydration enthalpy than sodium ion

  • magnesium is a smaller ion and has a greater charge

  • so higher charge density than sodium ion

  • so attracts water more strongly

  • (delta- oxygen)

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in terms of electrostatic forces determine why electron affinity has a negative value

electrostatic force of attraction between nucleus and external electron

energy released when electron added

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what 2 factors make up the perfect ionic model

  • perfectly spherical

  • only electrostatic force of attraction between ions/no covalent character

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what type of value does born haber depict for enthalpies

experimental value

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why is there a difference between theoretical and experiemnetal enthalpies

as ionic lattice has covalent character

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gibbs equation

gibbs free energy = enthalpy change - temp x entropy of system

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gibbs energy =

-temp x entropy total

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temperature where feasible =

enthalpy change / entropy of system

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reaction is feasible when

temperature below 0

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why is the entropy 0 at 0K, state in terms of molecules

  • at 0K molecules have no energy

  • so no disorder of molecules

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why does the graph slope upwards from the origin

as Temperature increases, entropy increases

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explain with the aid of a thermodynamical equation how free gibbs energy can be shown by a line

use whiteboard

  • state equation

  • state which parts coorespond ot y=mx+c

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why is the evaporation of water spontaneous even though it is endothermic

  • molecules more disorded when water evaporate

  • positive entropy change

  • TdeltaS > deltaH

  • deltaG < 0

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what is entropy?

the measure of disorder

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calculate entropy

products entropy - reactants entropy

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as temperature increases…

entropy increases and disorder increases

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feasible is interchangeable with…

spontaneous

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label all parts of a free gibbs energy graph

  • free gibbs energy - y-axis

  • temperature - x-axis

  • -entropy of system - gradient

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