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Chemistry A-Level > **3.1.4 Energetics** > Flashcards

**3.1.4 Energetics** Flashcards

1
Q

Bond breaking is…

A
  • Endothermic.
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2
Q

Bond making is…

A
  • Exothermic.
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3
Q

How do we determine whether a reaction is endo or exothermic?

A
  • Sum of energy in vs energy out.
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4
Q

Transition state?

A
  • State at which chemical bonds are partially formed + broken.
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5
Q

Activation energy meaning?

A
  • Minimum energy needed for reactant molecules to have a successful collision + start the reaction.
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6
Q

Do exothermic or endothermic reactions have a higher activation energy?

A
  • Endothermic.
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7
Q

Is enthalpy change +ve or -ve in exothermic?

A
  • -ve.
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8
Q

Is enthalpy change +ve or -ve in endothermic?

A
  • +ve.
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9
Q

Where does the activation energy occur?

A
  • Between reactants + transition state.
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10
Q

Where does enthalpy change occur?

A
  • From reactants to products.
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11
Q

What is enthalpy?

A
  • Total chemical energy inside a substance.
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12
Q

What symbols represent enthalpy change?

A
  • ΔH.
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13
Q

Exothermic reactions are thermodynamically possible because…

A
  • Enthalpy of the reactants is higher than products.
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14
Q

What are 2 examples of exothermic reactions?

A
  • Combustion.
  • Neutralisation.
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15
Q

What is an example of an endothermic reaction?

A
  • Thermal decompostion.
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16
Q

What is enthalpy change?

A
  • Energy change of system at constant pressure.
17
Q

What are standard conditions?

A
  • 1 atm / 100kPa.
  • 25℃.
18
Q

℃ to K?

A
  • ℃ + 273 = K.
19
Q

What is standard enthalpy of formation?

A
  • ΔH of 1 mole of compound is formed from its constituent elements in standard conditions w/ reactants + products in standard state.
20
Q

What is standard enthalpy of combustion?

A
  • ΔH of 1 mole of substance is burned completely in oxygen in standard conditions w/ reactants + products in standard states.
21
Q

What is heat?

A
  • Sum of all particle’s energy ∴ affected by amount of substance.
22
Q

What is temperature?

A
  • Related to mean kinetic energy of particles in a system ∴ independent of particles present.
23
Q

How can you calculate enthalpy change from experimental data?

A
  • Q=mcΔT.
24
Q

How does a flame calorimeter differ from a simple calorimeter?

A
  • Reduces heat loss to surroundings to obtain more accurate results.
  • Spiral chimney of copper.
  • Enclosed flame.
  • Burnt in pure oxygen as opposed to air.
25
Q

How to measure enthalpy change for reaction occurring in (aq)?

A
  • Expanded polystyrene cup as calorimeter.
  • Measure temp change of solution.
  • Heat capacity of solution –> 4.18.
  • Density –> 1g/cm3.
26
Q

How can experimental determination of enthalpy change be more accurate?

A
  • Cooling curves.
27
Q

What is Hess’ law?

A
  • ΔH of reaction is same regardless of route taken.
28
Q

What is enthalpy of an element?

A
  • 0.
29
Q

What is bond dissociation enthalpy?

A
  • ΔH required to break a covalent bond w/ all species in gaseous state.
  • Differs for same bond in different molecules.
30
Q

What is mean bond enthalpy?

A
  • Average value for bond dissociation enthalpy of a given bond.
31
Q

Why may experimental methods for enthalpy determination not be very accurate?

A
  • Heat lost to surroundings.
  • Not in standard conditions.
  • Reaction may not be complete.
32
Q

Why is using bond enthalpies not as accurate as using standard enthalpy of combustion/formation?

A
  • Bond enthalpies are a mean across diff molecules.
  • ΔH of combustion/formation apply to just that molecule ∴ more accurate.
33
Q

What is underneath the equation in enthalpy of combustion?

A
  • The oxides of the elements.
34
Q

In enthalpy of combustion do the arrows point towards or away from the middle?

A
  • Towards.
35
Q

What is underneath the equation in enthalpy of formation?

A
  • The elements in their standard states.
36
Q

In enthalpy of formation do the arrows point towards or away from the middle?

A
  • Away.

Chemistry A-Level (12 decks)

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