Topic 5 & 15 - Energetics Flashcards

1
Q

What is an open system?

A

A system that can exchange energy and matter with the surroundings

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2
Q

What is a closed system?

A

A system that can exchange energy but not matter with the surroundings

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3
Q

What is an exothermic reaction?

A

A reaction in which heat is given out by the system

∆H is negative and is treated as a product

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4
Q

What is an endothermic reaction?

A

A reaction in which heat is absorbed by the system

∆H is positive and treated as a reactant

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5
Q

What is standard enthalpy change, ∆H?

A

The heat energy transferred under standard conditions

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6
Q

What does the increase in temperature depend on?

A
  1. The mass of the object
  2. The amount of heat added
  3. The nature of the substance
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7
Q

What is the specific heat capacity?

A

The heat needed to increase the temperature of unit mass by 1 K

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8
Q

What kind of processes are combustion and neutralisation?

A

Exothermic

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9
Q

What is the relationship between stability and enthalpy level?

A

The higher the enthalpy level, the smaller the stability

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10
Q

What is enthalpy of combustion?

A

The heat produced when one mole of a substance is burned in excess oxygen

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11
Q

What is Hess’s law

A

The enthalpy change for any chemical reaction is independent of the route, provided the starting conditions and final conditions are the same:

∆H1 + ∆H2 = ∆H3

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12
Q

What is average bond enthalpy?

A

The energy needed to break one mole of bonds in gaseous molecules under STP

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13
Q

What does an endothermic process involve in terms of bonds?

A

Involves the separation of particles which are held together by a force of attraction (breaking bonds)

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14
Q

What does an exothermic process involve in terms of bonds?

A

The bringing together of particles which have an attractive force between them (forming bonds)

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15
Q

What is standard enthalpy change of formation, ∆Hf?

A

The enthalpy change that occurs when one mole of the substance is formed from its elements in their standard states under STP

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16
Q

What is the standard state of a substance?

A

The pure form of the substance under STP

17
Q

What is the standard enthalpy change of formation for an element?

A

Zero

18
Q

What is the enthalpy change of formation of a reaction?

A

∆Hreaction = Σ∆Hf(products) - Σ∆Hf(reactants)

19
Q

What is the standard enthalpy change of combustion, ∆Hc?

A

The enthalpy change that occurs when one mole of the substance burns completely under STP

20
Q

What is the enthalpy change of a combustion reaction?

A

∆Hreaction = Σ∆Hc(reactants) - Σ∆Hc(products)

21
Q

What is the first electron affinity, ∆He?

A

The enthalpy change when one mole of gaseous atoms attracts one mole of electrons

Cl(g) + e(g) → Cl(g)

22
Q

What is the lattice enthalpy, ∆Hlat?

A

The enthalpy change that occurs when one mole of a solid ionic compound is separated into gaseous ions under STP

NaCl(s) → Na+(g) + Cl(g)

23
Q

What is the enthalpy change of atomisation, ∆Hatom?

A

The heat change that occurs when one mole of gaseous atoms are formed from the element in its standard state

Na(s) → Na(g)

24
Q

How does lattice enthalpy change with charge and size of particles?

A

It increases with higher ionic charge and smaller ionic radii due to attractive forces

25
Q

What is the entropy change of a system?

A

∆Sreaction = Σ∆S(products) - Σ∆S(reactants)

26
Q

What is the relationship between the change in entropy of the surroundings and the change in enthalpy of a system?

A
27
Q

What is the sign of ∆Gsys for a spontaneous process?

A

Negative

28
Q

What is the Gibbs’ free energy for a reaction?

A

∆G = ∆H - T∆S

29
Q

What is the ∆Gsys a measure of?

A

The spontaneity of a reaction:

  • negative → spontaneous
  • positive → non-spontaneous
30
Q

How can ∆Gsys be used to predict the feasibility of a reaction?

A

At low temperature:

∆Gsys ≈ ∆Hsys (T∆S ≈ 0)

At high temperature

∆Gsys ≈ –T∆Ssys (T is high enough to make ∆H negligible)

31
Q

What is the ∆G of a reaction?

A

∆Greaction = ∑∆Gf(products) - ∑∆Gf(reactants)

32
Q

What is the ∆G of an element in its standard state?

A

Zero