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A level Chem > Enthalpy Definitions > Flashcards

Enthalpy Definitions Flashcards

1
Q

When is a reaction endothermic overall?

A
  • Energy is absorbed to break bonds
  • Energy is released to form bonds
  • More energy is absorbed during bond breaking than is released during bond forming
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2
Q

When is a reaction exothermic overall?

A
  • Energy is absorbed to break bonds
  • Energy is released to form bonds
  • More energy is released during bond forming than is absorbed during bond breaking
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3
Q

What are standard conditions?

A
  • 298K
  • 100kPa
  • 1moldm-3
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4
Q

What is first ionisation energy?

A
  • The energy change when 1 mole of electrons are removed from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
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5
Q

Is first ionisation energy endothermic or exothermic?

A
  • Endothermic
  • As energy needed to overcome the electrostatic attraction between positive proton and negative electron
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6
Q

Write equation for first ionisation energy of Sodium

A

Na(g) —-> Na+(g) + e-

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7
Q

What is first electron affinity?

A
  • The energy change when 1 mole of gaseous atoms gain 1 mole of electrons to form 1 mole of gaseous 1- ions
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8
Q

Is first electron affinity endothermic or exothermic?

A
  • Exothermic
  • Energy is released when forming the electrostatic attraction between positive proton and negative electron
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9
Q

Write equation for first electron affinity of Oxygen

A

O(g) + e- —–> O-(g)

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10
Q

What is second electron affinity?

A
  • The energy change when 1 mole of gaseous 1- ions gain 1 mole of electrons to form 1 mole of gaseous 2-ions
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11
Q

Is second electron affinity endothermic or exothermic?

A
  • Endothermic
  • Energy needed to overcome repulsion between negative ion and negative electron
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12
Q

Write equation for second electron affinity of Oxygen

A

O-(g) + e- —-> O2-(g)

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13
Q

What is standard enthalpy change of combustion?

A
  • Enthalpy change when 1 mole of a substance completely burns in excess oxygen, under standard conditions
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14
Q

Is standard enthalpy change of combustion endothermic or exothermic?

A
  • Exothermic
  • As more energy is released by bond forming than is absorbed by bond breaking
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15
Q

Write an equation for standard enthalpy change of combustion of Methane

A

CH4(g) +2O2(g) —–> CO2(g) + 2H2O(l)

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16
Q

What is standard enthalpy change of formation?

A
  • Enthalpy change when 1 mole of a compound is formed from its elements in their standard states, under standard conditions
17
Q

Write equation for standard enthalpy change of formation of Ethanol

A

2C(s) + 3H2(g) + 1/2O2(g) —–> C2H6O(l)

18
Q

What is the state of Methane, Ethane, Propane and Butane?

19
Q

What is standard enthalpy change of formation of elements?

20
Q

What is the state of alkanes from Pentane onwards?

21
Q

What is the state of alcohols?

22
Q

What is standard enthalpy change of neutralisation?

A
  • Enthalpy change when an acid and alkali are neutralised to form 1 mole of water, under standard conditions
23
Q

Write equation for standard enthalpy change of neutralisation of Sulfuric Acid + Sodium Hydroxide

A

1/2H2SO4(aq) + NaOH(aq) —–> 1/2Na2SO4(aq) + H2O(l)

24
Q

Is standard enthalpy change of neutralisation endothermic or exothermic?

A
  • Exothermic
  • Bond forming whilst making water releases more energy than energy which is absorbed during bond breaking
25
Q

What is enthalpy change of atomisation?

A
  • Enthalpy change when 1 mole of gaseous atoms are formed from an element in its standard state
26
Q

Write equation for enthalpy change of atomisation for Cl

A

1/2Cl2(g) —–> Cl(g)

27
Q

Is enthalpy change of atomisation endothermic or exothermic?

A
  • Endothermic
  • More energy is absorbed during bond breaking than energy which is released during bond forming
28
Q

What is lattice enthalpy?

A
  • Enthalpy change for the formation of 1 mole of an ionic compound from its gaseous ions, under standard conditions
29
Q

Write equation for lattice enthalpy of Magnesium Chloride

A

Mg2+(g) + 2Cl-(g) —-> MgCl2(s)

30
Q

Is lattice enthalpy endothermic or exothermic?

A
  • Exothermic
  • As more energy is released during the formation of electrostatic attraction between oppositely charged ions than energy absorbed
31
Q

What is standard enthalpy change of hydration?

A
  • Enthalpy change when 1 mole of gaseous ions dissolve completely in water to form 1 mole of aqueous ions, under standard conditions
32
Q

Write equation for standard enthalpy change of hydration of Magnesium

A

Mg2+(g) —-> Mg2+(aq)

33
Q

Is standard enthalpy change of hydration endothermic or exothermic?

A
  • Exothermic
  • As formation of attractive force between water and ions releases more energy than is absorbed
34
Q

What is enthalpy change of solution?

A
  • Enthalpy change when 1 mole of a compound is completely dissolved in water
35
Q

Write enthalpy change of solution of Magnesium Chloride

A

MgCl2(s) ——> Mg2+(aq) + 2Cl-(aq)

A level Chem (6 decks)

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