Physical Chemistry Key phrases

Question 1

negative enthalpy - is this exothermic or endothermic? Why?

Answer 1

Exothermic because heat is being released into the surroundings, making the chemicals in the reaction more stable, releasing heat into the surroundings.

Question 2

positive enthalpy - is this exothermic or endothermic? Why?

Answer 2

Endothermic because heat is taken into the chemicals from the surroundings, lowering the temperature of the surroundings

Question 3

What has happened to the model of the atom over time?

Answer 3

Concept of an atom has changed from being a single undivided particle to having neutrons, protons and electrons in a sphere to the present day model where there are electron shells and a nucleus containing protons and neutrons.

Question 4

Relative mass and charge of neutrons, protons and electrons

Answer 4

Protons: mass = 1, charge =+1
Neutrons: mass = 1, charge =0
Electrons: mass = 1/1840, charge = - 1

Question 5

What are the symbols for mass number and atomic number?

Answer 5

Mass number is A
Atomic number is Z

Question 6

How do you find the number of neutrons, protons and electrons?

Answer 6

Number of protons = atomic number,
Number of electrons = the atomic number - charge
Number of neutrons = mass number - atomic number

Question 7

How do electron shells fill in electron configuration? What are the types of subshell and how many electrons can each hold?

Answer 7

Electrons fill in energy order filling the subshell before moving on to the next. although as s is further away in space but lower in energy than d from the 3d subshell onwards s fills and empties before d.

There are 4 types of electron subshell, s,p,d and f. s holds up to 2, p holds up to 6, d holds up to 10, f holds up to 14.

Question 8

What’s an ionisation energy?

Answer 8

The minimum energy required to remove 1 mole of electrons from 1 mole of gaseous ions..

Question 9

Full electron configuration vs short hand electron configuration

Answer 9

Full electron configuration shows all the electrons in their subshells. Short hand condenses the subshells into [noble gas] with electron configuration.

Question 10

First ionisation energy - trend in period 3, reasons, and the exceptions.

Answer 10

Increases across a period as the nuclear charge increases and the atomic radius stays the same.

Exception - Al as Al has the first electron in 3p which is higher in energy then 2 s so easier to remove.
Exception - S - has the first spin pair repulsion in 3p

Question 11

First ionisation energy - trend down group 2

Answer 11

decreases as atomic radius increases weakening attraction from outer electrons to the nucleus

Question 12

Generic Equation for first ionisation/electron bombardment (with state symbols)

Answer 12

M(g) –> M(g) + e-

Question 13

Key phrases to describe electron bombardment/impact

Answer 13

(for atoms/small molecules/molecules you want to make fragments of)
High energy electrons
From electron gun.
Fired at sample.
Knocks off one electron.
Has to happen in the gas phase.

Question 14

Electrospray ionisation generic equation

Answer 14

M(g)+H+ –> MH+(g)

Question 15

Electrospray ionisation key phrases

Answer 15

(for large molecules/molecules you don’t want to fragment)
Sample dissolved in volatile solvent
Injected as an aerosol through needle
Needle has a high positive charge
Sample gains a H+ ion

Question 16

Key phrases - mass spec - acceleration

Answer 16

Positive ions are accelerated by a negative electric field to a constant kinetic energy

Question 17

What happens in ion drift? Key phrases?

Answer 17

The positive ions with smaller m/z values will have the same kinetic energy as those with larger m/z and will move faster.

The heavier particles move slower

The ions are separated by different flight times

Question 18

What happens in mass spec - detection - key phrases?

Answer 18

For each isotope the mass spectrometer can measure a m/z (mass/charge ratio)and an abundance.

Each ion of the same mass hits the detector plate at the same time.
Each ion gains an electron.

This flow of electrons is a current that is measured. The current is proportional to abundance.

Question 19

How do you determine Mr from the mass spec read out? What’s the difference between electrospray and electron impact?

Answer 19

Look for the molecular ion peak, which is the peak furthest to the right of the graph that isn’t tiny.

For Electron impact/bombradment the m/z =Mr

If you’re using electrospray as well as the above you need to remember to take 1 away from the m/z to find the Mr

Question 20

How to prepare a stock solution

Answer 20

Weigh out the desired mass of the compound into a weighing boat.
Record the mass of the compound + weighting boat. Add the compound into a beaker and reweigh the weighing boat and record this new mass. Dissolve the solid in 100cm3 water. Transfer the solution into a volumetric flask. Wash the container, stirring rod and funnel and add the washings to the volumetric flask. Fill the volumetric flask with distilled water, until the bottom of the meniscus is at the graduation mark . Invert.

Question 21

Key Phrases about Giant covalent lattices and the 4 common giant covalent lattices.

Answer 21

Diamond, Graphite, silicon and silicon dioxide are the 4 common giant covalent lattices.

Key phrases - Giant covalent lattice contain many strong covalent bonds which causes their properties. Covalent bonds have a shared pair of electrons.

graphite has delocalised electrons and van der Waals forces between layers

Question 22

Coordinate/Dative bond

Answer 22

Special type of covalent bond where both electrons come from one atom called a coordinate bond or dative bond

Question 23

Key phrases around giant ionic lattices and how to spot them.

Answer 23

How to spot them: They’re either containing ammonium (NH4+) or a metal and at least one non-metal.

Giant ionic lattices/(ionic bonds) have strong electrostatic attraction between oppositely charged ions. Larger ions and lower charges have weaker attraction.

Question 24

Key phrases around giant metallic lattices and how to spot them

Answer 24

How to spot them - These compounds are just metals on their own.

The atoms lose their outer electrons causing the molecule to have delocalised electrons (forming metal cations)

Key phrase - Giant metallic lattices have strong electrostatic attraction between delocalised electrons and positively charged ions. Larger ions and lower charges have weaker attraction.

Question 25

Giant ionic lattices - Properties

Answer 25

Properties
Ionic compounds conduct electricity when melted or in solution, have high melting points and are the second strongest structure and second strongest bond.

Question 26

Giant Metallic lattice - Properties

Answer 26

Properties
Metallic compounds conduct electricity, have high melting points, are ductile, malleable and are the third strongest structure and third strongest bond.

Question 27

Define electronegativity

Answer 27

Electronegativity is the ability of an atom to attract a bonding pair of electrons in a covalent bond.

Question 28

What effects electronegativity? How to spot electronegative elements at a level?

Answer 28

Electronegativity is affected by having a smaller atomic radius and larger number of protons.

The most electronegative element is F. N, O and then Cl and the next most electronegative. This can be used to help compare electronegativity.

Question 29

Simple molecular compounds -description

Answer 29

Simple molecular compounds are the most common crystal structure for covalent molecules. They have bonds holding atoms together to make molecules. The molecules are held together as solids and liquids by forces between the molecules.

Question 30

Define polar bonds and what causes them/cancels them out

Answer 30

Polar bonds are bonds that have a permanent uneven distribution of electron density caused by a large difference in electronegativity. Symmetrical molecules the electronegative elements pull in equal and opposite directions so cancel.

Question 31

Hydrogen bonding - What is it? Key phrases around it? Where is it between? How is it represented in diagrams?

Answer 31

Misnamed – this is not a bond but is the strongest intermolecular force
Key Phrases:
The electrostatic attraction in a hydrogen bond is between the lone pair on the N/O/F and the ∂+ hydrogen on a different molecule attached to a N/O/F. This attraction is between molecules

This is represented as a dotted line.

Question 32

Permanent Dipole-Dipole forces key phrases and what cases them.

Answer 32

This kind of intermolecular force is caused by the large difference in electronegativity between two elements in a covalent bond. It is the second strongest intermolecular force.

This creates a polar bond where one of the elements is usually one of N/O/F/Cl. This, more electronegative, element is ∂-. The other element is less electronegative, such as C, H or other elements further to the left of the periodic table. This less electronegative element is ∂+.

The attraction is between molecules, this time between the ∂+ atom in one molecule and the ∂- in the other molecule. This is shown with a dotted line.

Question 33

van der Waals’ forces key phrases/description

Answer 33

Key description
It is caused by a random movement of electrons causing a temporary dipole in that molecule (with a small d+ and d-). This partial charge then causes electron density to be attracted/repelled in other nearby molecules which induces a dipole in them.

Van Der Waals’ forces are the weakest intermolecular force, but the larger the surface area of the electron cloud (or the larger the molecule) the stronger this intermolecular force is as the size of the partial charge will increase. This can mean for large molecules van der waal’s forces are stronger between molecules than other intermolecular forces

Question 35

Scaffold for doing melting point comparisons

Answer 35

When asked questions about melting points it’s essential to identify the crystal structure of the materials being compared. You need to discuss the forces/bonds that hold them together. The list below is in order of melting point from highest to lowest.
Diamond, graphite, silicon and silicon dioxide are giant covalent lattices (macromolecular). Bonds break to melt this.
metal and a non-metal is a giant ionic lattice, Forces of attraction are overcome.
Metals (usually alone) are giant metallic lattices. Forces of attraction are overcome.
2 or more non-metals bonded together tend to be simple molecular. Forces of attraction are overcome between molecules (chose most relevant of the three intermolecular forces)

Question 36

Method of calculating the number of bonding pairs and lone pairs

Answer 36

number of electrons = group number + bonds - charge
electron pairs = number of
electrons/2
number of lone pairs = electron pairs - bond pairs

Use coordination number for complexes not shapes

Question 37

List of the key shapes of molecules, their bond angle and examples and bond angles - 2 bonding pairs

Answer 37

Question 38

List of the key shapes of molecules, their bond angle and examples and bond angles - 3 bonding pairs

Answer 38

Question 39

List of the key shapes of molecules, their bond angle and examples and bond angles - 4 bonding pairs

Answer 39

Question 40

List of the key shapes of molecules, their bond angle and examples and bond angles - 2 bonding pairs 2 lone pairs

Answer 40

Question 41

List of the key shapes of molecules, their bond angle and examples and bond angles - 3 bonding pairs 1 lone pair

Answer 41

Question 42

List of the key shapes of molecules, their bond angle and examples and bond angles - 5 bonding pairs

Answer 42

Question 43

List of the key shapes of molecules, their bond angle and examples and bond angles - 6 bonding pairs

Answer 43

Question 44

List of the key shapes of molecules, their bond angle and examples and bond angles - 4 bonding pairs with d8 electrons or 2 lone pairs

Answer 44

Question 45

Define enthalpy change

Answer 45

Enthalpy change (∆H) is the heat energy change measured under conditions of constant pressure.

Question 46

What are standard conditions?

Answer 46

100 kPa,
298 K,

Question 47

What’s Hess’ law

Answer 47

Enthalpy change is independent of the route taken

Question 48

What are collisions and successful collisions?

Answer 48

Collisions - When particles hit into each other

Successful collisions - When particles hit into each other and react as particles
have energy greater than or equal to the activation
energy

Question 49

Define activation energy

Answer 49

The minimum energy required for a reaction to occur

Question 50

Define Catalyst

Answer 50

A chemical that lowers the activation energy by providing an alternate reaction pathway, without being used up.

Question 51

Effect of changing temperature on rate?

Answer 51

As temperature increases/decreases the number of particles with energy equal to or greater than the activation energy increases/decreases. This greatly increases/decreases the frequency of successful collisions.

Question 52

Effect of changing pressure in gases, concentration in liquids or surface areas in solids?

Answer 52

Closer/More/more spread out particles
The number of collisions increases so the number of successful collisions increases in proportion. (reverse also true)

Question 53

Effect of having added a catalyst to rate of reaction?

Answer 53

The proportion of particles with energy equal to or greater than the activation energy increases so the number of successful collisions increases.

Question 54

Key features of a Maxwell Boltzmann distribution?

Answer 54

Question 55

Define mean bond enthalpy

Answer 55

The average enthalpy change when 1 mole of a specific bond is broken in the gas phase.

Question 56

Why are values from calorimetry inaccurate? (3 reasons)

Answer 56

Heat loss/incomplete combustion/heat absorbed by equipment

Question 57

Explain why values from mean bond enthalpy calculations differ from those determined using Hess’s law

Answer 57

Values from Hess’s law are for specific chemicals, where as values from mean bond enthalpies are averaged over a wide variety of compounds.

Question 58

What is dynamic equilibrium?

Answer 58

forward and reverse reactions proceed at equal rates
the concentrations of reactants and products remain constant

Question 59

What is Le Chatelier’s Principle?

Answer 59

The equlibrium will shift to oppose the change

Question 60

Scaffold for applying Le Chatelier’s Principle.

Answer 60

The equilibrium will shift to the ______ side to oppose _______ by _______.

May also need to comment on yield – the more to the right of the equilibrium the bigger the yield.

Question 61

What variable is the only variable that Kc/Kp/Ka/Kw and k depend on

Answer 61

Temperature

Question 62

What’re the key rules for calculating oxidation state?

Answer 62

Oxidation states are a measure of how many electrons have been lost
Elements have an oxidation state of 0,
Chemicals in compounds will usually have the oxidation state of their group number, except for the chemical you’re asked to work out in the exam
Helpful to remember H is +1 and O is -2 except for in peroxide which is +1
The more electronegative element is always negative.

Question 63

How to balance a redox equation

Answer 63

Construct half equation
Balance the Subject of the half equation (using big numbers)
Balance the Oxygens by adding in water (H2O)
Balance the hydrogens by adding in H+
Balance the overall charge on each side of the equation by adding in electrons (e-)
Subject
Oxygens
Hydrogens
Charge

Question 64

What is oxidation and reduction?

Answer 64

Oxidation – is loss of electrons,
Reduction – is gain of electrons,

Question 65

What’s an oxidising and reducing agent?

Answer 65

Reducing agent – is a chemical that causes reduction and is itself oxidised,
Oxidising agent - is a chemical that causes oxidation and is itself reduced,

Question 66

How are half equations combined?

Answer 66

multiply half equations until there is the same number of electrons in each half equation (one set of electrons is in the reactants and one in the products so these should cancel).

Question 67

How do cells work?

Answer 67

Reaction between two metals
and their ions in solution, the more
reactive metal is reduced
The more reactive electrode’s
metal atoms become ions, donating
electrons through wires to the less
reactive electrode where ions in the
solution gain electrons and become
part of the metal electrode

Question 68

What’s a salt bridge used for? What’s a common salt bridge?

Answer 68

Salt bridge completes the circuit
KNO3 is the standard chemical for a
salt bridge

Question 69

What’s the standard hydrogen electrode? What are the conditions? What kind of electrodes should be used?

Answer 69

Platinum electrodes should be used when another electrode
won’t work as they’re a gas/liquid/mix of ions

All ions should have a concentration of 1 moldm-3,
Pressure should be 100 kPa,
Temperature should be 298 K

Question 70

What are the rules for making a cell diagram?

Answer 70

The solid vertical line represents the boundary between phases e.g. solid (electrode) and solution (electrolyte) *The double line represents the salt bridge between the two half cells
*the voltage produced is indicated *the more positive half cell is written on the right if possible (but this is not essential)
If a system does not include a metal that can act as an electrode, then a platinum electrode must be used and included in the cell diagram. It provides a conducting surface for electron transfer. A platinum electrode is used because it is unreactive and can conduct electricity. (surface are of the electrodes has no impact on the reaction)

Question 71

How to calculate the emf of a cell from a cell diagram?

Answer 71

emf = E°right - E°left

Question 72

How to calculate the emf of a cell with no diagram?

Answer 72

emf = Ered - Eox
(This assumes that the cell is feasible)

Question 73

What does a negative emf tell you?

Answer 73

that the cell’s reaction isn’t feasible

Question 74

Define emf

Answer 74

Cell emf is the maximum potential difference between two electrodes of a cell

Question 75

What’s the electrode potential of a standard hydrogen electrode in V?

Answer 75

0 V

Question 76

What’s the emf of the measured electrode in the standard hydrogen electrode equal to? Why?

Answer 76

emf = E°right

The standard hydrogen is on the left because that means the electrochemical potential of that cell is the value read on the voltmeter. This is because hydrogen’s E0 = 0

Question 77

What’s the electrochemical series?

Answer 77

The electrochemical series is the list of electrochemical potentials in numerical order
The series is shown as equilibrium (even though it usually just has straight common forward arrows)

Question 78

Scaffold for using the electrochemical series?

Answer 78

The golden rule – Most positive is reduced
Use this rule to identify the equation to examine,
reducing agents are on the right, oxidising agents are on the left,
Then select the chemical that is being the oxidising agent or the reducing agent in that chemical .

Question 79

Scaffold for writing equations using electrochemical series

Answer 79

The golden rule – the most positive is reduced for discharging cells, reverse for recharging cells,
Reducing agents are on the right and oxidising agents are on the left.
Electrons must cancel

Question 80

Non-rechargeable cells - key info

Answer 80

Electrochemical cells can be used as a commercial source of energy.
No cell of any type is necessarily at standard conditions.
There are issues around disposal so there are waste issues.
Contain chemicals that get used up over time and eventually their emf drops to 0 as the energy gets converted into other forms (light/heat etc).

Question 81

Key facts about rechargeable cells

Answer 81

The cells chemicals can be restored by charging them and causing the reaction to reverse.
There’s less waste, it’s cheaper in the long run and has lower environmental impact. There are still some waste issues at end of life of cell.
Discharging follows the golden rule for electrochemistry (most positive is reduced)
Recharging is the opposite to the golden rule the most positive is oxidised, the most negative is reduces during recharging

Question 82

Half equations for the lithium ion cell, charging and discharging equations,

Answer 82

Positive electrode:
Li+ + CoO2 + e– → Li+[CoO2]–

Negative electrode: Li → Li+ + e–

In use: CoO2 + Li  LiCoO2
Charging: LiCoO2  CoO2 + Li

Question 83

Equation for hydrogen fuel cells

Answer 83

Question 84

What is a fuel cell?

Answer 84

Fuel cells are somewhat different to other cells.
They have a continuous supply of the chemicals into the cell and so neither run out of chemicals nor need re-charging.
There are acid versions of the cell but their overall equation is the same so the emf of the cell is the same.

Question 85

Using fuel cells as a fuel source, drawbacks and benefits.

Answer 85

Drawbacks:
Hydrogen is hard to transport and store easily as it is a gas.
Hydrogen is flammable and explosive (but this is true of most fuels).
Hydrogen is usally made using fossil fuels.
High cost of hydrogen fuel.

Benefits:
Only waste product is water,
Do not need recharging,
very efficient.

Question 86

Enthalpy of formation definition and symbol

Answer 86

deltaHf

Enthalpy change when one mole of a substance is formed from its constituent elements with all substances in their standard states

Question 87

Definition and symbol Enthalpy of combustion

Answer 87

Enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in standard states

Question 88

Enthalpy of neutralisation definition and symbol

Answer 88

Enthalpy change when 1 mole of water is formed in a reaction between an acid and alkali under standard conditions

Question 89

Definition - First Ionisation enthalpy

Answer 89

First ionisation energy = enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions.

Question 90

Definition Second ionisation enthalpy

Answer 90

Second ionisation energy = enthalpy change when each ion in one mole of gaseous 1+ ions loses one electron to form one mole of gaseous 2+ ions.

Question 91

Define first electron affinity

Answer 91

First electron affinity = enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1– ions.

Question 92

Define second electron affinity

Answer 92

Second electron affinity = enthalpy change when each ion in one mole of gaseous 1– ions gains one electron to form one mole of gaseous 2– ions.

Question 93

Define Enthalpy of atomisation

Answer 93

Enthalpy change when one mole of gaseous atoms is produced from an element in its standard state.

Question 94

Define Hydration Enthalpy

Answer 94

Enthalpy change when one mole of gaseous ions become hydrated (dissolved in water).

Question 95

Define Enthalpy of solution

Answer 95

Enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other.

Question 96

Define bond dissociation enthalpy

Answer 96

Enthalpy change when one mole of covalent bonds is broken in the gaseous state.

Question 97

Define Lattice enthalpy of formation

Answer 97

Enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in the gas phase

Question 98

Define Lattice enthalpy of dissociation

Answer 98

Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase

Question 99

Define Enthalpy of vaporisation

Answer 99

Enthalpy change when one mole of a liquid is turned into a gas

Question 100

Define Enthalpy of fusion

Answer 100

Enthalpy change when one mole of a solid is turned into a liquid

Question 101

Golden rules for making born haber cycles

Answer 101

Make only one change at a time,
Start by making compounds gasesous atoms if you can,
Remove electrons from positive ion one mole at a time until the desired charge is reached,
Add electrons one mole at a time until the desired charge is reached.

Question 102

What’s the equation to calculate enthalpy of solution from a Hess cycle?

Answer 102

enthalpy of solution = lattice enthalpy of dissociation + enthalpy of hydration

Question 103

Calculating values from calorimetry?

Answer 103

List the values in the question
Convert the units
Find q from q=mc∆T
Find ∆H using ∆H=q/1000/n
Put in the sign

Question 104

Scaffold for calculating values from born haber cycles

Answer 104

Identify each enthalpy change in the Born-Haber cycle and label them with symbols
Put in the data for each enthalpy change you’ve identified and make sure you’ve put in multipliers where needed. (all enthalpy definitions use one mole, bond dissociation enthalpy = 2xatomisation enthalpy)
Change the sign on any arrows in the cycle not moving in the same direction
Construct an equation by adding up all the enthalpies and making it equal zero
Rearrange equation to find unknown
Put numbers into your equation to solve

Question 105

What is the perfect ionic model?

Answer 105

The perfect ionic model suggests that all ions are perfectly spherical and the charge is found in the centre (point charges)
Larger anions bonded to small cations tend to have more covalent character as smaller cations distorts (polarises) the electron density of the larger anion
The bigger the difference between the lattice enthalpy and the theoretical value the more covalent character. More covalent character the stronger the ionic bond.

Question 106

What does the size of the lattice enthalpy of formation/dissociation tell you about the compound?

Answer 106

The larger in magnitude the value then the stronger the ionic bond is.

Question 107

What is entropy?
What keyword must you use when discussing entropy?

Answer 107

Entropy is a measurement of how disordered a system (chemical) is.

Disorder is an essential keyword

Question 108

Sketch the shape of an entropy graph and explain the shape of it.

Answer 108

Question 109

In what ways can entropy effect reactions?

Answer 109

Some reactions can be favoured by entropy (due to an increase in disorder)

If there is an increase in the total number of particles in the products compared to the reactants there is an increased in disorder so there’s an increase in entropy.

This can lead to an increase in the likelihood of a reaction taking place.

Question 110

What is Gibb’s free energy? (definition and equation)

Answer 110

Gibbs’ Free energy is the total energy available in a substance/substances that can be used in a chemical reaction

Question 111

How can we tell if a reaction is feasible?

Answer 111

Gibbs free energy change (∆G)can allow us to identify if a reaction is feasible or not. If ∆G is 0 or less then a reaction is feasible.

We can estimate the direction of Gibbs free energy change by looking at the equation and the direction of the values in it.

Question 112

What can the directions of entropy and enthalpy tell us about the feasibility of a reaction?

Answer 112

Question 113

How can Gibbs free energy link to straight line graphs?

Answer 113

Question 114

What is rate measured in?

Answer 114

The rate of a reaction is measured as the change in concentration per second (moldm-3s-1).

Question 115

Generic expression for rate of a reaction, including what possible orders are and what k depends on.

Answer 115

The rate of a chemical reaction is related to the concentration of reactants by a rate equation of the form:
Rate = k[A]m [B]n
Where m and n are the orders of reaction with respect to reactants A and B and k is the rate constant.
The orders m and n are restricted to the values 0, 1, and 2.
The rate constant k varies with temperature

Question 116

What is an overall order of reaction?

Answer 116

Overall order – is the total of the indices (total orders) in a rate equation

Question 117

What is a rate determining step?

Answer 117

The rate determining step is the slowest step in a reaction

Question 118

How can you identify a catalyst from a rate equation?

Answer 118

It’s in the rate equation but not in the overall rate equation.

Question 119

How do you identify the rate determining step?

Answer 119

If a chemical is not represented in the rate equation it’s not in the rate determining step.

The chemical can be represented by an intermediate.

Question 120

How can concentration time graphs be used to determine the order of a reaction?

Answer 120

Question 121

What’s an initial rate method?

Answer 121

Initial rate – rate measured over the first few seconds to keep concentration known, starting concentration(s) changed and rate measured again.

Question 122

What’s a continuous rate method?

Answer 122

Continuous rate – measured the change in concentration over time for the whole experiment

Question 123

How do rate concentrations graphs link to order of reactions?

Answer 123

Question 124

What do mole fractions add up to?

Answer 124

1

Question 125

What do partial pressures add up to?

Answer 125

The total pressure

Question 126

What effect does a catalyst have on the position of equilibria/yield/Kp/Kc? Why?

Answer 126

No effect, because catalysts increase the rate of forwards and reverse reactions equally

Question 127

What is a buffer?

Answer 127

A mixture of a weak acid and a weak base that resists small changes in pH

Question 128

How does a buffer resist small changes in pH?

Answer 128

The weak acid reacts with the added in OH- and the weak base can react with the added in H+

Question 129

Why is [H2O] incorporated into Kw?

Answer 129

Because the value is so large it is practically constant as it hardly changes.

Question 130

What is an equivalence point?

Answer 130

When the moles of the two compounds in a titration are equivalent in proportion so totally react.

Question 131

How should you select an indicator? What’s the limit on indicators?

Answer 131

This is where the indicator should be changing colour at to ensure an accurate colour change.

Indicators are mostly weak acids so if too much is added then that can make the titration inaccurate.

Indicators that change over the small range of weak acids/weak base titrations are very hard to select as the indicator must change colour over a very small pH range.

Question 132

Key phrase about symmetry and dipoles

Answer 132

Key phraseidea that dipole moments (or dipoles) cancel out due to symmetry

Question 133

Draw the structure of diamond

Answer 133

Question 134

Draw the structure of graphite

Answer 134

Question 135

Draw the structure of silicon

Answer 135

Question 136

Draw the structure of silicon dioxide

Answer 136

Question 137

Draw the structure of sodium chloride

Answer 137

Question 138

Draw the structure of sodium

Answer 138

Question 139

Draw the structure of ice

Answer 139

Question 140

Draw the structure of iodine

Answer 140

Question 141

Excess

Answer 141

When the moles of a compound is greater in proportion to their molar ratio than needed to react with other reactant.

Question 142

Limiting Reagent

Answer 142

When the moles of a compound is less in proportion to their molar ratio than needed to react with other reactant..