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chemistry > R1.2 - enthaly changes in reactions > Flashcards

R1.2 - enthaly changes in reactions Flashcards

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1
Q

What type of reaction is bond breaking?

A

Endothermic reaction which requires energy.

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2
Q

What type of reaction is bond making?

A

Exothermic which releases energy.

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3
Q

What is bond enthalpy?

A

Bond enthalpy - energy needed to break 1 mole of bonds of gaseous molecules under standard conditions.

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4
Q

What is average bond enthalpy?

A

Average bond enthalpy - energy needed to break 1 mole of bonds of gaseous molecules under standard conditions averaged over similar compounds.

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5
Q
A
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6
Q

What is a covalent bond?

A

Electrostatic attraction between a shared pair of negative electrons and the positive nuclei of a bonded atom.

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7
Q

What is the relationship between bond enthalpy and bond length, amount of bonds and polarity?

A

Shorter bond length = Higher bond enthalpy
Longer bond length = Lower bond enthalpy
More bonds = Higher bond enthalpy
Less bonds = Lower bond enthalpy
Polar bonds = Higher bond enthalpy
Non-Polar bonds = Lower bond enthalpy

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8
Q

How can you calculate bond enthalpy?

A

Bond enthalpy = bond energies broken - bond energies made
Bond enthalpy = products - reactants

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9
Q

What is Hess’s Law?

A

Hess’s Law - states that the enthalpy change for a reaction is independent of it’s pathway between initial and final states, with reactants and products being the same.

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10
Q

What is standard enthalpy change of formation?

A

Standard enthalpy change of formation - enthalpy change that occurs when 1 mole of a substance is formed from it’s elements in their standard states when they are stable (283K and 100kPa).

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11
Q

What is standard enthalpy change of combustion?

A

Standard enthalpy change of combustion - enthalpy change that occurs when 1 mole of a substance burns completely under standard conditions.
- Must have a negative value.

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12
Q

In what direction does Hess’s triangle face for enthalpies of combustion and formation?

A

Formation - Formed in Heaven - upwards
Combustion - Burned in Hell - downwards

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13
Q

When giving a question asking to calculate enthalpy of formation/combustion, but you are given the opposite values, which values should you use?

A

Use the values you are told and given

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14
Q

Why are standard enthalpy changes of formation calculations useful?

A
  • Gives a measure of the stability of a substance relative to its elements
  • Can be used to calculate the enthalpy changes of all reactions; either hypothetical and real.
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15
Q

What is the standard enthalpy of formation for an element?

A

0

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16
Q

What are standard states?

A

The form of an element at standard conditions - usually the most stable.

17
Q

What is a Born-Haber cycle?

A

Born-Haber cycle - an application of Hess’s law, used to show the energy changes in the formation of an ionic compound.

18
Q

What is first ionization energy?

A

First ionization energy - the minimum energy required to remove 1 mole of electrons from 1 mole of gaseous atoms.

19
Q

What is electron affinity?

A

First electron affinity - enthalpy change when one mole of gaseous electrons is added to 1 mole of gaseous atoms.

20
Q

What is lattice enthalpy?

A

Lattice enthalpy - enthalpy change that occurs when 1 mole of a solid ionic compound is separated into gaseous ions under standard conditions.

21
Q

What is enthalpy change of atomization?

A

Enthalpy change of atomization - enthalpy change that occurs when 2 moles of gaseous atoms is formed from the element in its standard state.

22
Q

Why are experimental lattice enthalpies larger than theoretical lattice enthalpies?

A
  • Theoretical values are based on an ionic model and doesn’t take into account additional covalent contributions to the bonding.
23
Q

What type of reaction is lattice enthalpy?

A

Endothermic reactions - all values are positive.

24
Q

What type of reaction is enthalpy change of atomization?

A

Exothermic

25
Q

What type of reaction is enthalpy change of formation?

A

Exothermic

26
Q

What type of reaction is ionization enthalpy?

A

Endothermic

27
Q

What type of reaction is bond enthalpy?

A

Endothermic

28
Q

What type of reaction is first electron affinity?

A

Exothermic

29
Q

What type of reaction is second electron affinity?

A

Endothermic

30
Q

What is the relationship between bond enthalpy and enthalpy change of atomization?

A

Bond enthalpy = x2 Enthalpy of atomization
Bond enthalpy - starts with 1 mole
Enthalpy of atomization - makes 1 mole

31
Q

What is the trend between lattice enthalpy and ionic charge?

A

Lattice enthalpy is proportional to the product of the charges on the positive and negative ions.
- The larger the ionic charge, the larger the lattice enthalpy.

32
Q

What is the trend between lattice enthalpy and ionic radius?

A

Lattice enthalpy is inversely proportional to the sum of the ionic radii of the positive and negative ions.
- The larger the ionic radius, the smaller the lattice enthalpy.

chemistry (22 decks)

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