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Chemistry > Energetics(1) > Flashcards

Energetics(1) Flashcards

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1
Q

Enthalpy and enthalpy change

A
  • enthalpy is the energy content of a substance under constant pressure
  • enthalpy change of reaction is the energy change in a chemical reaction when the molar quantities of reactant specified in the chemical equation react to form products
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2
Q

Endothermic and Exothermic reactions

A
  • breaking bond requires energy and is endothermic
  • formation of bonds produces energy and is exothermic
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3
Q

Standard conditions and standard states

A
  • pressure: 1 bar (105Pa)
  • temperature: 298K
  • concentration: 1 mol dm-3
  • standard state of a substance is its most stable form under standard conditions
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4
Q

What is the standard enthalpy change of reaction

A
  • the amount of heat absorbed or evolved when molar quantities of reactants as shown in chemical equation react together under standard condition of 298K and 1 bar
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5
Q

What is standard enthalpy change of formation

A
  • the amount of heat absorbed or evolved when one mole of substance is formed from its constituents elements, all in their standard states at 298K and 1 bar
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6
Q

What is standard enthalpy change of combustion

A
  • amount of heat evolved when one mole of a substance in its standard state is completely burned in excess oxygen under standard conditions of 298K and 1 bar
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7
Q

What is standard enthalpy change of neutralisation

A
  • the amount of heat evolved when one mole of water is formed from the neutralisation between an acid and base, under standard conditions of 298K and 1 bar
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8
Q

What is standard enthalpy change of atomisation
- standard enthalpy change of atomisation of a compound

A
  • the amount of heat absorbed when one mole of free gaseous atom is formed from its element under standard conditions of 298K and 1 bar
  • the amount of heat absorbed when one mole of compound in its standard state is broken into gaseous atoms of its constituent elements under standard conditions of 298K and 1 bar
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9
Q

What is bond energy

A
  • bond energy of a covalent bond is the average amount of heat absorbed to break one mole of the covalent bond in gaseous state under standard conditions of 298K and 1 bar
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10
Q

What is electron affinity
- first EA
- second EA

A
  • the amount of heat absorbed or evolved when one mole of electrons is added to one mole of gaseous atoms to form one mole of singly charged gaseous anions (mostly exothermic)
  • the amount of heat absorbed when one mole of gaseous singly charged gaseous anion to form one mole of doubly charged gaseous anion (always endothermic)
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11
Q

What is lattice energy

A
  • the amount of heat evolved when one mole of solid ionic compound is formed from its constituent free gaseous ions under standard conditions of 298K and 1 bar (always exothermic)
  • measure of ionic bond strength
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12
Q

What affects lattice energy

A
  • charge on ion:
    — as charge of ion increases (q+xq-) increases
    — electrostatic forces of attraction between the ions becomes stronger
    — lattice energy becomes more exothermic
  • radius of ion
    — as size of ion increases, inter-ionic distance (r++r-) increases
    — electrostatic forces of attraction between the ions becomes weaker
    — lattice energy becomes less exothermic
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13
Q

What is standard enthalpy change of hydration

A
  • the amount of heat evolved when one mole of free gaseous ions is dissolved in a large amount of water forming a solution at infinite dilution at 298K and 1 bar (always negative)
  • measure of strength of ion-dipole interaction
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14
Q

What affects standard enthalpy change of hydration

A
  • charge density:
    — higher charge and smaller ionic radius will lead to
    — stronger ion-dipole attractions between the ion and water molecules
    — more exothermic
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15
Q

What is enthalpy change of solution

A
  • the amount of heat absorbed or evolved when one mole of a solute is dissolved in an infinite volume of water under standard conditions of 298K and 1 bar
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16
Q

What does Hess Law state about constant heat summation

A
  • enthalpy change of a chemical reaction is dependent only on the initial states of the reactants and the final states of the products and is independent of the reaction pathway taken

Chemistry (24 decks)

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