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A-LEVEL CHEMISTRY > A2 Energetics I > Flashcards

A2 Energetics I Flashcards

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1
Q

Define Enthalpy Change of Reaction

A
  • The enthalpy change that accompanies a reaction in the molar quantaties specified in the chemical equation
  • Under standard conditions with all reactants and products in their standard states
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2
Q

Define Enthalpy Change of Formation

A
  • The enthalpy change that takes place when one mole of a substance is formed from it’s elements
  • Under standard conditions, with all reactants and products in their standard states
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3
Q

Define Enthalpy Change of Combustion

A
  • The enthalpy change that takes place when one mole of a substance reacts completely with oxygen
  • Under standard conditions, with all reactants and products in their standard states
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4
Q

Define Enthalpy Change of Neutralisation

A
  • The enthalpy change that accompanies the reaction of an acid and a base to form one mole of liquid water
  • Under standard conditions, with all reactants and products in the standard states
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5
Q

What enthalpy do exothermic reactions have

A

Negative enthalpy

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6
Q

What enthalpy do endothermic reactions have

A

Positive enthalpy

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7
Q

What enthalpy is heating water, and therefore what is the problem with accurate readings when water is heated

A
  • Heating water is endothermic
  • Enthalpy cannot be measured
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8
Q

Draw an enthalpy profile diagram for an exothermic reaction

A
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9
Q

Draw an enthalpy profile diagram for an endothermic reaction

A
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10
Q

Define Activation Energy

A

The minimum energy required to break all the bonds in the reactants, allowing the reaction to take place

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11
Q

What are standard conditions

A
  • 298K
  • 100kPa
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12
Q

What is the standard state of a substance

A

The physical state of a compound under standard conditions

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13
Q

Define Average Bond Enthalpy

A

The enthalpy change when 1mol of gaseous covalent bonds are broken

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14
Q

Explaination for why reactions are exothermic

A
  • Bond breaking absorbs energy
  • Bond making releases energy
  • More energy released than absorbed
  • (H) negative
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15
Q

Explaination why reactions are endothermic

A
  • Bond breaking absorbs energy
  • Bond making releases energy
  • More energy absorbed than released
  • (H) positive
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16
Q

Bond energy calculation equation

A
17
Q

What must always be remembered when structuring bond enthalpy calculations

A

Always write the total enthalpy of bonds broken and bonds made

18
Q

Steps to a combustion calorimetry calculation

A
  • Determine energy transferred to water
  • Determine moles of fuel used
  • Determine enthalpy
19
Q

Combustion calorimetry equation for energy transferred to water (symbol + word)

A
20
Q

Combustion calorimetry equation for moles of fuel used (symbol + word)

A
21
Q

Combustion/solution calorimetry equation for determination of enthalpy (symbol + word)

A
22
Q

Solution calorimetry equation for moles of fuel used (symbol + word)

A
23
Q

What are the reasons as to why calculated enthalpy data is different for both solution and combustion calorimetry AND how to reduce this effect

A
  • Heat loss to surroundings - use bomb calorimeter
  • Data book uses standard values - use standard conditions
  • Evaporation of water from beaker - place lid over beaker
24
Q

What are the reasons as to why calculated enthalpy data is different for combustion calorimetry AND how to reduce this effect

A
  • Incomplete combustion of fuel - burn in plentiful oxygen
  • Evaporation of alcohol from wick - place cap over wick when not burning
25
Q

Combustion calorimetry equation for energy transferred to water (symbol + word)

A
26
Q

Hess cycle for combustion and equation

A
27
Q

Hess cycle for formation and equation

A
28
Q

Theoretical Hess cycle for neutralisation

A
29
Q

What must always be remembered when carying out Hess cycle calculations

A

Add/Subtract data values according to arrow direction

30
Q

What must you always bear in mind when considering solution calorimetry, and molar ratios

A

Multiply H by however many moles of reagent you calculated in the equation

A-LEVEL CHEMISTRY (11 decks)

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