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Chemistry Revision > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

Define enthalpy change

A

the heat energy transferred in a reaction at constant pressure.

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2
Q

What are the standard conditions?

A

100kPa and 298K

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3
Q

Do exothermic reactions have a negative or positive enthalpy change?

A

negative

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4
Q

What is lattice formation enthalpy?

A

the enthalpy change when one mole of a solid compound is formed from its gaseous ions

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5
Q

What is lattice dissociation enthalpy?

A

the enthalpy change when one mole of a solid ionic compound is completely dissociated into its gaseous ions

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6
Q

What is enthalpy change of formation?

A

the enthalpy change when one mole of a compound is formed from its elements in their standard states
Ca(s) + Cl2(g) –> CaCl2(s)

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7
Q

What is bond dissociation enthalpy?

A

the enthalpy change when all the bonds of the same type in one mole of gaseous molecules are broken
Cl2(g) –> 2Cl(g)

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8
Q

What is the enthalpy change of atomisation of an element?

A

the enthalpy change when one mole of gaseous atoms is formed from an element in its standard state
1/2Cl2(g) –> Cl(g)

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9
Q

What is the enthalpy change of atomisation of a compound?

A

the enthalpy change when one mole of a compound in its standard state is converted to gaseous ions
NaCl(s) –> Na(g) + Cl(g)

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10
Q

What is the first ionisation energy?

A

the enthalpy change when one mole of gaseous 1+ ions is formed from one mole of gaseous ions
Mg(g) –> Mg+(g) + e-

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11
Q

What is the second ionisation energy?

A

the enthalpy change when one mole of gaseous 2+ ions is formed from one mole of gaseous 1+ ions
Mg+(g) –> Mg2+(g) + e-

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12
Q

What is the first electron affinity?

A

the enthalpy change when one mole of gaseous 1- ions is made from one mole of gaseous atoms
O(g) + e- –> O-(g)

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13
Q

What is the second electron affinity?

A

the enthalpy change when one mole of gaseous 2- ions is made from one mole of gaseous 1- ions
O-(g) + e- –> O2-(g)

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14
Q

What is the enthalpy of hydration?

A

the enthalpy change when one mole of aqueous ions is formed from gaseous ions
Na+(g) –> Na+(aq)

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15
Q

What is enthalpy of solution?

A

t he enthalpy change when one mole of an ionic substance dissolves in enough solvent to form an infinitely dilute solution

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16
Q

What does the purely ionic model of lattice assume?

A

all the ions are spherical and have their charge evenly distributed around them

17
Q

What is covalent character?

A

the negative and positive ions aren’t exactly spherical, positive ions polarise neighbouring negative ions to different extents. the more polarisation, he more covalent the bonding is

18
Q

What does it show if the experimental and theoretical lattice enthalpies for a compound are very different?

A

the compound has a lot of covalent character

19
Q

What happens when a solid ionic lattice dissolves in water?

A

the bonds between the ions break to give gaseous ions (lattice enthalpy of dissociation) and bonds between the ions and the water are made (enthalpy change of hydration)

20
Q

When calculating enthalpy change of solution, what is enthalpy change 1?

A

Lattice dissociation enthalpy

21
Q

When calculating enthalpy change of solution, what is enthalpy change 2?

A

enthalpy of hydration of both the positive and negative ions

22
Q

When calculating enthalpy change of solution, what is enthalpy change 3?

A

enthalpy change of solution

23
Q

What is entropy and what symbol represents it?

A

entropy tells you how much disorder there is, it is represented by the letter S

24
Q

What three things affect entropy?

A

physical state, dissolution and number of particles

25
Q

What state of matter has the highest entropy?

A

gas

26
Q

How can you increase the entropy of a solid?

A

dissolve a solid in solution

27
Q

How does number of particles affect entropy?

A

more particles=more entropy

28
Q

What is the calculation for working out entropy change?

A

entropy change=entropy of products-entropy of reactants

29
Q

What is free-energy change?

A

a measure used to predict whether a reaction is feasible

30
Q

What is a feasible reaction?

A

once started, it will carry on to completion without energy being supplied to it

31
Q

What is the formula for free-energy change?

A

free energy change(J/mol)=enthalpy change(J/mol)- temperature(K) x entropy change(J/K/mol)

32
Q

If the reaction is exothermic, how does this affect the entropy?

A

the entropy change will be positive

33
Q

If the reaction is endothermic, how does this affect the entropy?

A

the entropy change will be negative

34
Q

When will a reaction not be feasible?

A

when free-energy change is positive, when enthalpy and entropy are positive it won’t be feasible below certain temperatures

35
Q

When free-energy change is zero, is the reaction feasible?

A

yes, it is just feasible

Chemistry Revision (23 decks)

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