Energy

Front 1

Lattice enthalpy?

Back 1

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

Front 2

Hess' law?

Back 2

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.

Front 3

Standard enthalpy change of formation?

Back 3

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

Front 4

Enthalpy change of atomisation?

Back 4

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

Front 5

The first ionisation energy?

Back 5

The enthalpy change accompanying the removal of one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Front 6

Second ionisation energy?

Back 6

The enthalpy change accompanying the removal of one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

Front 7

The first electron affinity?

Back 7

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.

Front 8

The second electron affinity?

Back 8

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.

Front 9

Features of lattice enthalpy?

Back 9

It is an exothermic change. They have a negative sign because energy is given out when ionic bonds are being formed from gaseous ions.
Indicated the strength of an ionic lattice and is the measure of ionic bond strength.
Covalent substance does not have lattice enthalpy.
They cannot be measure directly.

Front 10

Standard enthalpy change of solution?

Back 10

Enthalpy change that takes place when one mole of a compound is completely dissolved in water and under standard conditions.

Front 11

What happens when a solid dissolves?

Back 11

Breakdown of the ionic lattice into gaseous ions.
Hydration of ions.

Front 12

Standard enthalpy change of hydration?

Back 12

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

Front 13

Breakdown of ionic lattice?

Back 13

Overcoming the attractive forces between the oppositely charged ions requires energy. Process is the exact opposite of producing of lattice enthalpy.

Front 14

Hydration?

Back 14

Gaseous ions bond with water molecules. Positively charged ions will be attracted to the slightly negative oxygen atoms in the water, and the negatively charged ions will be attracted to the slightly positive hydrogen atoms in the water.

Front 15

Two factors the govern the size of the lattice enthalpy?

Back 15

Ionic size and ionic charge.

Front 16

Ionic size?

Back 16

Small ions can pack together closely in a lattice and attract each other strongly. larger ions are further apart in their lattice and the forces of attractions between them are weaker.

As ionic radius increases:
Attractions decreases.
lattice enthalpy becomes less negative.

Front 17

Ionic charge?

Back 17

The compounds with the most negative lattice enthalpies are those which have small, highly charged ions.
When two highly charged ions of opposite charge are present in the lattice they attract each other strongly. A very exothermic reaction will take place.

Front 18

Ionic size- hydration?

Back 18

As the ionic radius becomes smaller, the value of the enthalpy of hydration becomes more negative. Hydration depends on the ability of the ion to attract and bond with water molecules. Small ions exert more attraction on water molecules and more energy is released.

Front 19

Ionic charge- hydration?

Back 19

As the charge on an ion increases it has a greater attraction for water molecules, and hence the hydration enthalpy is more negative.

Front 20

Entropy?

Back 20

The quantitative measure of the degree of disorder in a system.

Front 21

What can entropy tell us?

Back 21

A gas spreading through a room.
heat from a fire spreading through a room.
Ice melting in a warm room.
salt dissolving in water

Front 22

Idea of entropy?

Back 22

Things in nature tends to move from order to disorder In isolated systems.

Front 23

Calculating entropy change of reaction? and measurement.

Back 23

entropy is the sum of products minus the sum of reactants and is measured in JKMOL-1

Front 24

Entropy measure of randomness?

Back 24

If a change makes a system more random, S is positive.
If a change makes a system more ordered, S is negative.

Front 25

Standard entropy of reaction?

Back 25

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

Front 26

At 0K, perfect crystals have what entropy?

Back 26

Zero.

Front 27

Free energy change?

Back 27

Delta G is the balance between enthalpy, entropy and temperature for a process
Delta G = Delta H - T delta S.

Front 28

Energy from Entropy?

Back 28

Depends on the temp. As the temp increases, the energy derived from entropy becomes more significant.

Front 29

What three factors are depended on for a spontaneous reaction?

Back 29

The temperature
The entropy change
The enthalpy change.

Front 30

Feasibility of a reaction?

Back 30

Depends on the balance between enthalpy and entropy. Spontaneous processes happen when delta G is negative.

Front 31

Delta H Negative, Delta S positive?

Back 31

Delta G always negative, reactions feasible.

Front 32

Delta H Positive, Delta S negative?

Back 32

Delta G always positive and never feasible.

Front 33

Delta H negative and Delta S negative?

Back 33

Delta G is Negative at low temps, and therefore feasible at low temps.

Front 34

Delta H positive and Delta S positive?

Back 34

Delta G is negative at high temperature, and the reaction if feasible at high temps.

Front 35

Spontaneous processes?

Back 35

A process is spontaneous If a chemical system becomes more stable and its overall energy decreases. The overall energy decrease results from contributions from both enthalpy and entropy.

Front 36

Oxidation?

Back 36

Loss of electrons, or an increase in oxidation no.

Front 37

Reduction?

Back 37

Gain of electrons, or a decrease in oxidation no.

Front 38

Electricity from chemical reactions?

Back 38

In redox reactions, electrons are transferred. An electrochemical cell controls the electron transfer to produce electrical energy. The controlled transfer of electrons is the basis of all cells and batteries.

Front 39

Half cell?

Back 39

Comprises an element in two oxidation states. The simplest half cell has metal placed in an aqueous solution of its own ions.

Front 40

electrochemical cell made from two half cells?

Back 40

One half cell releases electron, and the other half gains electrons.

Front 41

Difference in electrode potential is measure with what?

Back 41

A voltmeter.

Front 42

Wire for a electrochemical cell?

Back 42

The wire connects the two metals, allowing electrons to be transferred between the two half cells. The voltmeter has a high resistance and used to minimise the current that flows. If a small bulb were to replace the voltmeter, the bulb would light up.

Front 43

Salt bridge from electrochemical cell?

Back 43

It connects the two solutions, allowing ions to be transferred between the half cells. A simple salt bridge can made out of a strip of filter paper soaked in an aqueous solution of an ionic compounds that does not react with either of the half- cell solution.

Front 44

Metal ion/ metal ion half cells?

Back 44

Half cell contains ions of the same element in different oxidation states. E.g fe3+ and fe2+

Front 45

Non-metal/ non-metal ion half cells?

Back 45

E.g hydrogen half cell compromises of hydrogen gas H2 and H+ ions (aq).

Front 46

Problem with non-metal/non-metal ion half cells?

Back 46

There is no electrode to connect wire to.

Front 47

Solution to problem with non-metal/non-metal ion half cell?

Back 47

A platinum electrode is places in the solution so that it is in contact with both H2 and H+ ions. The platinum is inert and does not react at all- its sole purpose to allow the transfer of electrons into and out of the half cell via a connecting wire.

Front 48

Standard hydrogen half cell?

Back 48

Hydrochloric acid, of conc 1 mol dm, as source of H+
Hydrogen gas H2, at 100kPa.
An inert platinum electrode.

Front 49

Standard electrode potential?

Back 49

The e.m.f of a half cell compared with a standard hydrogen half cell, measured at 298K with solution concentrations of 1 mol dm and as gas pressure of 100kPa.

Front 50

Cell reaction?

Back 50

Overall chemical reaction taking place in the cell.
The cell reaction is the sum of the reduction and oxidation half reactions taking place in each half cell.

Front 51

Standard cell potential?

Back 51

e.m.f between the two half cells making up the cell under standard conditions.
The standard cell potential of any cell is the difference between the standard electrode potentials of each half cell.

Front 52

How is a standard electrode potential measured?

Back 52

By connecting a standard half cell to a standard hydrogen half cell.

Front 53

E.M.F?

Back 53

Electromotive force is the voltage produced by a cell when no current flows.

Front 54

Non-rechargeable cells?

Back 54

Provide electrical energy until the chemicals have reacted to such an extent that the voltage falls. The cell is then 'flat' and discarded.

Front 55

Fuel cells?

Back 55

The cell reactions uses external supplies of a fuel and an oxidant, which are consumed and needs to be provided continuously. The cell will continue to provide electrical energy so long as there is a supply of fuel and oxidant.

Front 56

Rechargeable cells?

Back 56

The chemicals in the cell react, providing electrical energy. the cell reaction can be reversed during recharging- the chemicals in the cell are regenerated and the cell can be used again.

Front 57

Hydrogen-oxygen fuel cell?

Back 57

The 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 flow into the cell. Fuel cells do not need to be recharged.

Front 58

Advs of fuel cells, less pollution?

Back 58

Combustion of hydrocarbon fuels produces CO2, which contributes to the greenhouse effect. Incomplete combustion produces toxic carbon monoxide, which must be removed by catalytic converters.
Hydrogen rich fuels produce only small amount of CO2.

Front 59

Advs of fuel cells, greater effiency?

Back 59

A petrol engine is less than 20% efficient in converting chemical energy by the combustion of petrol. Much of the chemical energy is wasted as heat.
Hydrogen fuel cell vehicles are 40-60% efficient in converting the fuels energy.

Front 60

Limitations of hydrogen fuel cells?

Back 60

Fuel cells use toxic chemicals in their production.
Current 'adsorbers' and 'absorbers' of hydrogen have a limited lifetime.
Current fuel cells have a limited lifetime, requiring regular replacement and disposal following high production costs.
Feasibility of storing a pressurised liquid.

Front 61

Hydrogen economy?

Back 61

The use of hydrogen as a fuel has to be accepted politically and publically.
There are logistical problems in the handling and maintenance of hydrogen systems.
Hydrogen is an energy carrier and not an energy source. Hydrogen must first be manufactured, and the danger is that more energy is used in making hydrogen that is saved.

Front 62

Storage of hydrogen?

Back 62

Hydrogen can be stored as liquid under pressure. This in itself creates logistical problems. Even under pressure, a very low temp is required and liquid hydrogen will be need to stored in giant thermos flasks.
Hydrogen can be adsorbed onto the surface of a solid materials in.
Hydrogen can be absorbed with some solid materials.

Front 63

Generation of hydrogen gas?

Back 63

Hydrogen rich fuels include methanol, natural gas and petrol. These are mixed with water and converted into hydrogen gas by an on-board reformer. The reformed operates at 250-300 degrees to generate hydrogen gas.

Front 64

Advs of methanol?

Back 64

A liquid fuel is easier the store than hydrogen gas.
Methanol can be generated from biomass.

Front 65

Limitations of prediction using standard electrode potential- conc?

Back 65

Non standard conditions alter the value of the electrode potential. Equilibrium opposes the change my moving to right, the electron are removed from the equilibrium, the electrode potential becomes less negative, or more positive. A change in electrode potential resulting from conc changes means that predictions made on the basis of the standard value may not be valid.

Front 66

Limitations of prediction using standard electrode potential- will a reaction take place?

Back 66

Predictions can be made about the equilibrium position but not about the reaction rate, which may be extremely slow due to high activation energy.
The actual conditions used for a reaction may be different from the standard conditions used to measure E values. This will affect the value of the electrode potential.
Standard electrode potentials apply to aqueous equilibria- many reactions take place under very different conditions.

Front 67

General working rule, electrode potential?

Back 67

larger the difference, the more likely a reaction will take place.
If difference is less than 0.4V, then a reactions if unlikely to take place.