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A Level Physical Chemistry > Section 4 - Energetics > Flashcards

Section 4 - Energetics Flashcards

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1
Q

Define enthalpy.

A

A measure of the heat content of a substance.

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2
Q

Define enthalpy change.

A

Change in heat content at a constant pressure.

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3
Q

What are the standard conditions for an enthalpy reaction?

A

100kPa and 298K

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4
Q

Define standard enthalpy change of formation.

A

The enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions.

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5
Q

Define enthalpy change of combustion.

A

The enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions.

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6
Q

Define enthalpy change of neutralisation.

A

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

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7
Q

What are the equations used in calorimetry?

A

1) q = mc/\T 2) moles = mass/Mr or conc x vol/1000 3) Enthalpy Change = q/moles

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8
Q

Define bond enthalpy.

A

The enthalpy change that occurs when one mole of a covalent bond is broken in the gaseous state.

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9
Q

What is the enthalpy change of an exothermic reaction?

A

Negative.

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10
Q

What is the enthalpy change of an endothermic reaction?

A

Positive.

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11
Q

Are oxidation reactions usually exo or endothermic?

A

Exothermic.

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12
Q

Are thermal decomposition reactions exo or endothermic?

A

Endothermic.

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13
Q

How is mean bond enthalpy calculated?

A

It is the average energy needed to break a certain type of bond over a range of compounds.

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14
Q

Are mean bond enthalpies always positive or negative?

A

Positive - endothermic.

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15
Q

How is enthalpy change calculated using mean bond enthalpies?

A

Total energy absorbed - Total energy released i.e. bonds broken - bonds formed.

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16
Q

How can you calculate enthalpy change of combustion using calorimetry? (3 steps)

A

1) Burn flammable liquid in calorimeter 2) Measure temp change of known mass of water 3) Use the equations

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17
Q

How can you calculate enthalpy change in solution using calorimetry? (5 steps)

A

1) Add known vol of acid to insulated container 2) Record temp 3) Add known volume of alkali 4) Stir and record temp at regular intervals 5) Use the equations

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18
Q

What are 3 issues with accuracy of calorimetry experiments?

A
  • Heat lost to surroundings - Incomplete combustion of fuel - Flammable liquids can evaporate
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19
Q

What is the q and its units in q=mc/\T?

A

heat lost or gained (J)

20
Q

What is the m and its units in q=mc/\T?

A

mass of water (or other solution) (g)

21
Q

What is the c and in q=mc/\T?

A

specific heat capacity

22
Q

What is the /\T and its units in q=mc/\T?

A

change in temp of water/solution (K)

23
Q

What is Hess’ Law?

A

The total enthalpy change is independent of the route taken.

24
Q

What is the enthalpy of formation of any element?

A

0

25
Q

What are the standard conditions for an enthalpy reaction?

A

100kPa and 298K

26
Q

Define standard enthalpy change of formation.

A

The enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions.

27
Q

Define enthalpy change of combustion.

A

The enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions.

28
Q

Define enthalpy change of neutralisation.

A

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

29
Q

What are the equations used in calorimetry?

A

1) q = mc/\T 2) moles = mass/Mr or conc x vol/1000 3) Enthalpy Change = q/moles

30
Q

Define bond enthalpy.

A

The enthalpy change that occurs when one mole of a covalent bond is broken in the gaseous state.

31
Q

What is the enthalpy change of an exothermic reaction?

A

Negative.

32
Q

What is the enthalpy change of an endothermic reaction?

A

Positive.

33
Q

Are oxidation reactions usually exo or endothermic?

A

Exothermic.

34
Q

Are thermal decomposition reactions exo or endothermic?

A

Endothermic.

35
Q

How is mean bond enthalpy calculated?

A

It is the average energy needed to break a certain type of bond over a range of compounds.

36
Q

Are mean bond enthalpies always positive or negative?

A

Positive - endothermic.

37
Q

How is enthalpy change calculated using mean bond enthalpies?

A

Total energy absorbed - Total energy released i.e. bonds formed - bonds broken

38
Q

How can you calculate enthalpy change of combustion using calorimetry? (3 steps)

A

1) Burn flammable liquid in calorimeter 2) Measure temp change of known mass of water 3) Use the equations

39
Q

How can you calculate enthalpy change in solution using calorimetry? (5 steps)

A

1) Add known vol of acid to insulated container 2) Record temp 3) Add known volume of alkali 4) Stir and record temp at regular intervals 5) Use the equations

40
Q

What are 3 issues with accuracy of calorimetry experiments?

A
  • Heat lost to surroundings - Incomplete combustion of fuel - Flammable liquids can evaporate
41
Q

What is the q and its units in q=mc/\T?

A

heat lost or gained (J)

42
Q

What is the m and its units in q=mc/\T?

A

mass of water (or other solution) (g)

43
Q

What is the c and in q=mc/\T?

A

specific heat capacity

44
Q

What is the /\T and its units in q=mc/\T?

A

change in temp of water/solution (K)

45
Q

What is Hess’ Law?

A

The total enthalpy change is independent of the route taken.

46
Q

What is the enthalpy of formation of any element?

A

0

A Level Physical Chemistry (9 decks)

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