Chemistry - Equilibria, Energetics and Elements - F325 - Energy (2)

Question 1

Define lattice enthalpy.

Answer 1

Lattice enthalpy is the enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.

Question 2

Is lattice enthalpy an exothermic or endothermic change?

Answer 2

Lattice enthalpy is an exothermic change.

Question 3

What does Hess’ law state?

Answer 3

Hess’ law states that if a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.

Question 4

Define the standard enthalpy change of formation.

Answer 4

The standard enthalpy change of formation is the enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

Question 5

Define the enthalpy change of atomisation.

Answer 5

The enthalpy change of atomisation is the enthalpy change that takes place when one mole of gaseous atoms forms from the element in its standard state.

Question 6

Is atomisation an exothermic or endothermic reaction?

Answer 6

Atomisation is always an endothermic reaction; bonds are being broken.

Question 7

Define the first ionisation energy.

Answer 7

The first ionisation energy is the enthalpy change accompanying the removal of one electron from each atom in one mole of gaseous atoms to give one mole of gaseous 1+ ions.

Question 8

Define the second ionisation energy.

Answer 8

The second ionisation energy is the enthalpy change that accompanies the removal of one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

Question 9

Define the first electron affinity.

Answer 9

The first electron affinity is the enthalpy change accompanying the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.

Question 10

Define the second electron affinity.

Answer 10

The second electron affinity is the enthalpy change accompanying the addition of one electron to each ion in one mole of gaseous 1- ions to form one mole of gaseous 2- ions.

Question 11

Where do elements always sit in Born-Haber cycles?

Answer 11

Elements always sit on the zero line in Born Haber cycles.

Question 12

Define the standard enthalpy change of solution.

Answer 12

The standard enthalpy change of solution is the enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions.

Question 13

Define the standard enthalpy change of hydration.

Answer 13

The standard enthalpy change of hydration is the enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions.

Question 14

What are the two factors that govern the size of lattice enthalpy?

Answer 14

Ionic size and ionic charge are the two factors that govern the size of lattice enthalpy.

Question 15

As the ionic radius increases, what happens to the lattice enthalpy?

Answer 15

As the ionic radius increases, the attraction between the ions decreases and the lattice enthalpy becomes less negative.

Question 16

The compounds with the most negative lattice enthalpies have what type of ions?

Answer 16

The compounds with the most negative lattice enthalpies have small, highly charged ions.

Question 17

How does the ionic radius being smaller affect the enthalpy change of hydration?

Answer 17

As the ionic radius becomes smaller, the value of the enthalpy change of hydration becomes more negative.

Question 18

Define entropy.

Answer 18

Entropy, S, is the quantative measure of the degree of disorder in a system.

Question 19

What letter is used to represent entropy?

Answer 19

S is used to represent entropy.

Question 20

Why do all substances possess some degree of disorder?

Answer 20

All substances possess some degree of disorder because particles are always in constant motion.

Question 21

Define the standard entropy change of a reaction.

Answer 21

The standard entropy change of a reaction ΔS, is the entropy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being n their standard states.

Question 22

Which processes can occur spontaneously at room temperature?

Answer 22

Many exothermic processes take place spontaneously at room temperature.

Question 23

Whether a process is spontaneous or not depends on what three main factors?

Answer 23

Temperature T in kelvin
Entropy change in the system ΔS
Enthalpy change ΔH with the surroundings

Question 24

Define the free energy change.

Answer 24

The free energy change ΔG is the balance between enthalpy, entropy and temperature for a process: ΔG = ΔH - TΔS

Question 25

What has to be true of free energy for a process to take place spontaneously?

Answer 25

A process can take place spontaneously when ΔG

Question 26

Oxidation is a(n) …….. in oxidation number.

Answer 26

Oxidation is an increase in oxidation number.

Question 27

Reduction is a(n) ………… in oxidation number.

Answer 27

Reduction is a decrease in oxidation number.

Question 28

A half cell comprises what?

Answer 28

A half cell comprises an element in two oxidation states.

Question 29

The electrode potential of the half cell indicates what?

Answer 29

The electrode potential of the half cell indicates its tendency to lose or gain electrons in this equilibrium.

Question 30

What is the difference in electrode potential between two half cells measured with?

Answer 30

The difference in electrode potential between two half cells is measured with a voltmeter.

Question 31

The wire that connects the two half cells allows transfer of what?

Answer 31

The wire that connects the two half cells allows transfer of electrons.

Question 32

The salt bridge that connects the two half cells allows transfer of what?

Answer 32

The salt bridge that connects the two half cells allows transfer of ions.

Question 33

Which electrode releases electrons more easily?

Answer 33

The negative electrode releases electrons more easily.

Question 34

What kind of electrode is used in a non-metal half cell?

Answer 34

A platinum electrode is used in a non-metal cell.

Question 35

What is used as the reference for the measurement of voltages in electrochemical cells?

Answer 35

A standard hydrogen half cell is used as the reference for the measurement of voltages in electrochemical cells.

Question 36

Define the electromotive force.

Answer 36

The electromotive force (emf) is the voltage produced by a cell when no current flows.

Question 37

Define the standard electrode potential of a half cell.

Answer 37

The standard electrode potential of a half cell Estandard, is the emf of a half cell compared with the standard hydrogen half cell, measured at 298K with solution concentrations of 1moldm-3 and a gas pressure of 100kPa

Question 38

Species react with other species with a more …….. electrode potential than their own.

Answer 38

Species react with other species with a more positive electrode potential than their own.

Question 39

If the Estandard value is less than ………. then a reaction is unlikely to take place.

Answer 39

If the Estandard value is less than 0.4V then a reaction is unlikely to take place.