5.2 Energy (completed)

Question 1

Define lattice enthalpy

Answer 1

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

Question 2

What kind of energy change will lattice enthalpy always be?

Answer 2

Exothermic

Enthalpy change is negative

Question 3

What is the Born-Haber cycle?

Answer 3

A way of indirectly calculating lattice enthalpy from other known energy changes.

Question 4

What is the formation of gaseous atoms and what energy change is it?

Answer 4

Changing elements in their standard states into gaseous atoms.
Endothermic as it involves bond breaking.

Question 5

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Answer 5

Exothermic.

Question 6

Define standard enthalpy change of formation

Answer 6

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.

Question 7

Define standard enthalpy change of atomisation

Answer 7

The enthalpy change that takes place for the formation of one mole of gaseous atoms from the element in its standard state under standard conditions.

Question 8

Define first ionisation energy

Answer 8

The enthalpy change required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 9

Why is ionisation energy always endothermic?

Answer 9

Energy is required to overcome the attraction between a negative electron and a positive nucleus.

Question 10

Define first electron affinity

Answer 10

The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.

Question 11

Why is first electron affinity always exothermic?

Answer 11

Electron being added is attracted in towards the nucleus.

Question 12

Why are successive electron affinities endothermic?

Answer 12

The negative ion repels the additional electron, so energy is required to force the electron onto it.

Question 13

Define standard enthalpy change of solution

Answer 13

The enthalpy change that takes place when one mole of a solute dissolves in a solvent.

Question 14

What happens for a solid ionic compound to dissolve in water?

Answer 14

Ionic lattice breaks up

Water molecules are attracted to and surround the ions.

Question 15

Define enthalpy change of hydration

Answer 15

The enthalpy chnage that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions

Question 16

Describe the effect of ionic size on lattice enthalpy and melting point

Answer 16

Ionic radius increases
Attraction between ions decreases
Lattice enthalpy becomes smaller (less negative)
Melting point decreases

Question 17

Describe the effect of ionic charge on lattice enthalpy and melting point

Answer 17

Ionic charge increases
Attraction between ions increases
Lattice enthalpy becomes greater (more negative)
Melting point increases

Question 18

Describe the effect of ionic size on hydration enthalpy

Answer 18

Ionic radius increases
Charge density decreases
Attraction between ions and water molecules decreases
Hydration enthalpy becomes smaller (less negative)

Question 19

Describe the effect of ionic charge on hydration enthalpy

Answer 19

Ionic charge increases
Attraction between ions and water molecules increases
Hydration enthalpy becomes greater (more negative)

Question 20

Why is hydration enthalpy an inaccurate method of predicting solubility?

Answer 20

Many compounds with endothermic enthalpy changes of solution are soluble

Question 21

Define entropy

Answer 21

A measure of the dispersal of energy and order within in a system

Question 22

What are the units of entropy?

Answer 22

J/K/mol

Question 23

How does entropy relate to physical states?

Answer 23

In order of size of entropy value:

Gases > liquids > solids

Question 24

Define standard entropy

Answer 24

The entropy of one mole of a substance, under standard conditions (always positive)

Question 25

How is an entropy change calculated for a reaction?

Answer 25

Products - Reactants

Question 26

What is feasibility?

Answer 26

Whether a reaction is able to happen and is energetically feasible (or spontaneous)

Question 27

What is the equation for free energy change?

Answer 27

ΔG = ΔH -TΔS

Question 28

What is the requirement for the free energy change such that a reaction is feasible?

Answer 28

ΔG < 0 | A decrease in free energy

Question 29

Even though a reaction may have a negative value for ΔG, why might the reaction not take place at room temperature?

Answer 29

High activation energy resulting in a very slow rate

Question 30

Why does one ion have a higher lattice enthalpy than another? (3 Marks)

Answer 30

- Greater charge/charge density - As it is a smaller ion - Therefore a greater force of attraction and more energy required

Question 31

Why does one ion have a higher enthalpy of hydration than another? (3 Marks)

Answer 31

- Greater charge/charge density - As it is a smaller ion - Therefore a greater force of attraction to water

Question 32

How do you work out the enthalpy of solution?

Answer 32

Born-Haber Cycle: | Solution = Enthalpy of Hydration(s) - Lattice Enthalpy

Question 33

How do you write a redox equation in acidic conditions?

Answer 33

``` Write the overall unbalanced equation Write two half equations Balance the total electrons Combine Balance oxygen and hydrogen this with H+ and H2O ```

Question 34

How do you write redox equations in alkaline conditions?

Answer 34

Balance and acidic conditions Neutralise any H+ by adding OH- ions to both sides to produce water Final balance check

Question 35

What is the main difference between redox titrations and acid base titrations?

Answer 35

Redox titrations are self indicating and no indicator is needed

Question 36

What occurs in MnO4-/Mn2+ titrations with Fe2+?

Answer 36

Aqueous manganate is dark purple but aqueous manganese is colourless manganate loses its colour as it enters the iron solution and the endpoint is when there is a permanent pink tinge as all the Fe 2+ has been used up and will not decolourise the manganate

Question 37

What occurs in the I2/S2O3 2- titrations?

Answer 37

Iodide is a reducing agent and is colourless however aqueous iodine has a brown colour in atria solutions and deep blue black with a starch indicator By titrating it with Fitbit it can be used to assess the concentration of iodine

Question 38

What should you look for in titration equations?

Answer 38

Having to scale up for a different volume

Question 39

What does a salt bridge allowed for?

Answer 39

Ions to be transferred between half cells

Question 40

What are the conditions of a standard electrode?

Answer 40

298K 1atm 1.00 mol dm-3 ion solutions

Question 41

How do you measure the standard electrode potential of a half cell?

Answer 41

You can’t It is only possible to measure the difference of E between to have cells All half cells are measured against the standard hydrogen electrode SHE is given E of exactly 0

Question 42

What does the standard hydrogen electrode look like?

Answer 42

Platinum electrode H+ ion solution Supply of hydrogen at 1 atm Glass dome for hydrogen to bubble out

Question 43

What does the E values that are most positive do the best?

Answer 43

Gain electrons Reduce Oxidising agents

Question 44

What does the E values that are most negative do the best?

Answer 44

Lose electrons Oxidise Reducing agents

Question 45

What must you remember when drawing a half celf?

Answer 45

Salt bridge Platinum or other metal rod Volt meter Conditions

Question 46

How do you calculate the E value of the overall cell?

Answer 46

E positive terminal - E negative terminal

Question 47

How can use E values to decide whether something can reduce another?

Answer 47

Add the 2E values If the reaction is positive it will be spontaneous Remember to look to reverse E values if the equation is reversed

Question 48

What is the limitations of using E values to predict if one substance can reduce another?

Answer 48

Predictions are only valid under standard conditions High activation energy may mean reaction will take place very slowly Standard electrode potential is only applied to aqueous equilibria If the difference between E value is less than 0.4 V the reaction is unlikely to take place

Question 49

What are the two types of commercial cells?

Answer 49

Rechargeable and non-rechargeable

Question 50

What is a car battery consist of?

Answer 50

Several individual cells that are rechargeable

Question 51

What are two advantages of fuel cells?

Answer 51

Carbon dioxide contribute to climate change and greenhouse affect Fuel prices are rising and resources dwindling

Question 52

What are two disadvantages of fuel cells?

Answer 52

Safety of storage of hydrogen | Limited life-cycle of a cell – economic considerations

Question 53

What charge carriers are transferred through a) the wire b) the solution

Answer 53

a) electrons | b) ions

Question 54

What is a fuel cell?

Answer 54

An electrochemical cell that converts energy from the reaction of a fuel with oxygen into a voltage?

Question 55

What is the overall reaction for a hydrogen fuel cell?

Answer 55

2H2 + O2 → 2H2O