Energy

Question 1

What are key features of lattice enthalpy?

Answer 1

Exothermic, bonds formed, indicates strength of ionic lattice and ionic bond strength, not in covalent structure, cannot be measured directly

Question 2

What do arrows in born ha we cycle indicate?

Answer 2

Upwards are endothermic

Down are exothermic

Question 3

How do you calculate lattice enthalpy in Born Haber cycle?

Answer 3

Sum of clockwise enthalpy-sum of anti-clockwise enthalpy

Question 4

What happens when a solid dissolves?

Answer 4

Breakdown if ionic lattice into gaseous ions and hydration of ions

Question 5

How is ionic lattice broken down?

Answer 5

Separating ions, overcoming attractive forces requires energy, opposite to lattice enthalpy, endothermic, same magnitude

Question 6

What is hydration?

Answer 6

Hydration of gaseous ions, will bind with water molecules, positive attracted to slightly negative oxygen, negative attracted to hydrogen

Question 7

What does value of lattice enthalpy indicate?

Answer 7

Large is large electrostatic force of attraction between ions
Small is small force

Question 8

What factors govern lattice enthalpy?

Answer 8

Ionic size and ionic charge

Question 9

How does ionic size affect lattice enthalpy?

Answer 9

Small ions can pack more closely so attach strongly, larger are further apart so weaker force of attraction

Question 10

How does ionic charge affect lattice enthalpy?

Answer 10

Two highly charged ions attract more stingy then lower charges

Question 11

What compounds have highest lattice enthalpy?

Answer 11

Small radius and highly charged ions

Question 12

What affects enthalpy change of hydration?

Answer 12

Ionic size and ionic charge

Question 13

How does ionic size affect enthalpy of hydration?

Answer 13

As radius becomes smaller, enthalpy of hydration becomes more negative, depends on ability to attract water molecules and bond, small ions exert more attraction and more energy released

Question 14

How does ionic charge affect enthalpy of hydration?

Answer 14

As charge increases it has greater attraction to water molecules, more negative across period as size decreases and charge increases

Question 15

What is entropy?

Answer 15

Measure if disorder in a system, dispersal of energy, entropy increases when energy changes from being localised to being spread out, more disordered

Question 16

How is entropy change calculated?

Answer 16

Entropy of products -reactants

Question 17

What is a spontaneous reaction?

Answer 17

Process that proceeds on its own, leading to lower energy and increased stability

Question 18

What 3 things determine wether a process it spontaneous?

Answer 18

Temperature
Entropy change in a system
Enthalpy change with surroundings
For reaction to be feasible there must be decrease in overall energy derived from both the enthalpy change and the entropy of the solution

Question 19

How are energy and entropy related?

Answer 19

Entropy derived from overall energy depends on temperature, as temperature increases, energy derived from entropy becomes more significant

Question 20

How do you construct redox equation?

Answer 20

Identify oxidation numbers, balance any atom that changes oxidation number, identify total changes
Balance oxidation numbers of whole equation, total increase=total decrease

Question 21

What is an electrochemical cell?

Answer 21

Based on controlled transfer of electrons to produce electrical energy

Question 22

What is a half cell?

Answer 22

Comprises an element in two oxidation states

Question 23

How is a simple electrochemical cell set up?

Answer 23

Connecting two half cells together with differ t electrode potentials, one half cell releases electrons, the other gains electrons

Question 24

What is the role of the wire?

Answer 24

Connects two metals allowing electron transfer

Question 25

What is the role of the salt bridge?

Answer 25

Connects two solutions allowing transfer of ions, paper soaked in unreactive aqueous compound l, KNO3

Question 26

How are non metal/non metal half cells set up?

Answer 26

Non metal and aqueous ions in each half cell, no electrode, so platinum used as inert

Question 27

What is the cell reaction?

Answer 27

Sum of reduction and oxidation half reactions taking place in each half cell

Question 28

How is standard cell potential calculated?

Answer 28

Most negative is negative terminal, work out by positive terminal- negative terminal

Question 29

What is electrochemical series

Answer 29

Series of redox equilibria arranged with most negative sep value at the top, species at top have greatest tendency to release electrons, react to release with everything below

Question 30

What are limitations of predictions using standard electrode potentials?

Answer 30

Changes in electrode potential resulting from concentration changes means that predictions made of basis of standard value are not valid, reaction may not occur at a fast enough rate under conditions, only apply to aqueous equilibria

Question 31

What are electrochemical cells used for?

Answer 31

Source of electrical energy, work by having two redux equilibria with different electrode potentials

Question 32

What are non rechargeable cells?

Answer 32

Provide electrical energy until the chemicals have reacted to such an extent that the voltage falls, half and discarded

Question 33

Rechargeable cells

Answer 33

Chemicals react, provide energy, reaction can be reversed during recharging, chemicals regenerated and cell can be used again, such as nickel and cadium, or lithium ion and lotion polymer

Question 34

Fuel cells

Answer 34

Cell used external supply of fuel and oxidant, which are consumed and needs to be provided continuously, cell will continue to supply energy as long as there is fuel and oxidant

Question 35

What is a hydrogen-oxygen fuel cell?

Answer 35

Uses energy from reaction of fuel with oxygen to create a voltage. Reactants flow in and products flow out while the electrolyte remains in the cell. Fuel cells can operate virtually continuously so long as the fuel and oxygen continue to be supplies, more negative hydrogen system provides electrons, water is formed

Question 36

What hydrogen rich fuels are used in cars?

Answer 36

H gas used and methanol, natural gas or petrol

Question 37

What are the advantages of fuel cells?

Answer 37

Less pollution and less co2 | Greater efficiency

Question 38

How cAn hydrogen be stored?

Answer 38

As liquid under pressure in low temp Adsorbed into solid material Absorbed with solid material

Question 39

What are the limitations of fuel cells?

Answer 39

Large scale storage and transportation is difficult Feasibility of storing pressurised liquid Absobers and adsorbers have limited lifetime Fuel cells have short lifetime so need to be regularly replaces Use toxic chemicals in production

Question 40

What is hydrogen economy?

Answer 40

Needs to be accepted politically and by public | Logistical problems in handling and maintainable if system