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OCR A A-Level Inorganic Chemistry > Chapter 9 > Flashcards

Chapter 9 Flashcards

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1
Q

What is enthalpy (H)?

A
  • A measure of the heat energy in a chemical system
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2
Q

How is enthalpy change calculated?

A
  • Bond enthalpies of reactants - bond enthalpies of products
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3
Q

What is activation energy?

A
  • The minimum amount of energy required for a reaction to take place
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4
Q

How do we measure enthalpy change?

A
  • Under standard conditions
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5
Q

What are the standard conditions?

A
  • Pressure: 100 kPa
  • Temperature: 298 K
  • Standard states (physical states under these conditions)
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6
Q

What is standard enthalpy change, and its symbol?

A
  • The enthalpy change of a reaction when measured under standard conditions
  • ΔH^⦵
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7
Q

What is standard enthalpy change of reaction, and its symbol?

A
  • The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states
  • ΔrH⦵
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8
Q

How can the standard enthalpy change of reaction differ?

A
  • If you have the same chemical equation, but with each chemical shown to have twice the molar quantity, the standard enthalpy change of reaction also doubles, etc.
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9
Q

What is the standard enthalpy change of formation, and its symbol? Required.

A
  • The enthalpy change that takes place when one mole of a compound is formed from its elements under standard conditions, with all reactants and products in their standard states
  • ΔfH⦵
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10
Q

What is the standard enthalpy change of combustion, and its symbol? Required.

A
  • The enthalpy change that takes place when one mole of a substance is reacted completely with oxygen under standard conditions, with all reactants and products in their standard states
  • ΔcH⦵
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11
Q

What is the standard enthalpy change of neutralisation, and its symbol? Required.

A
  • The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H2O (l) under standard conditions, with all reactants and products in their standard states
  • ΔneutH⦵
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12
Q

What is the formula for specific heat capacity, and what do each of the symbols stand for? Include units.

A
  • q = mcΔT
  • q: heat energy (J)
  • m: the mass that changes temperature (g)
  • c: the specific heat capacity of the substance that changes temperature
  • ΔT: change in temperature measured
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13
Q

What is average bond enthalpy? Required.

A
  • When 1 mole of bonds of gaseous covalent bonds is broken
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14
Q

Write a symbol equation showing the bond enthalpy of Cl2.

A
  • Cl2 (g) -> 2Cl (g)
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15
Q

What are 2 limitations of average bond enthalpies?

A
  • The actual bond enthalpy varies according to the chemical environment of the bond (which other bonds the atoms are involved in)
  • Average bond enthalpy is calculated using the actual bond enthalpies from different chemical environments
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16
Q

Which processes are endothermic and exothermic?

A
  • Bond breaking is endothermic
  • Bond making is exothermic
17
Q

Describe an exothermic enthalpy profile diagram.

A
  • Enthalpy against progress of reaction
  • Products lower than reactants
  • Negative enthalpy change
18
Q

Describe an endothermic enthalpy profile diagram.

A
  • Enthalpy against progress of reaction
  • Products higher than reactants
  • Positive enthalpy change
19
Q

What is Hess’ law?

A
  • The overall enthalpy change of a reaction is independent of the route it takes
20
Q

How is the enthalpy change of combustion used to indirectly calculate the enthalpy change of a reaction?

A
  • The products from the combustion of the reactants/ products are written at the bottom
  • Arrows go down
  • The enthalpy change of combustion of the reactants and the products are used to calculate the enthalpy change
21
Q

How is the enthalpy change of formation used to indirectly calculate the enthalpy change of a reaction?

A
  • The elements needed to form the reactants/ products are written at the bottom
  • Arrows go up
  • The enthalpy change of formation for the reactants and the products are used to calculate the enthalpy change

OCR A A-Level Inorganic Chemistry (14 decks)

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