Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Alevel Chemistry > Thermodynamics, Rate Equations > Flashcards

Thermodynamics, Rate Equations Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

What are the orders for concentration’s influence on rate of reaction?

A

if no effect —>
Zero order A^0

if rate doubles when concentration doubles (direct proportion) —>
First Order A^1

if rate quadruples when concentration doubles —>
Second Order A^2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

The rate constant…

A
  • Different for every reaction
  • Varies with temperature
  • units are different for every reaction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is Enthalpy of Lattice Formation?

A

Enthalpy change when 1 mole of ionic lattice/solid ionic compound is formed from its gaseous ions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Why may the calculation of enthalpy for lattice formation based on the perfect ionic model give a smaller numerical value than the calculated value? e.g in the case of AgI

A

The Covalent character of the molecule

They may not be completely ionic.

the forces/bonds holding the matrix together are stronger.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Enthalpy change of formation

A

The enthalpu change when 1 mole of a compound is formed from it’s elements in their standard states under standard conditions.
(2Cs + 2H2aq –> C2H6aq)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Lattice enthalpy of formation

A

The enthalpy change when 1 mole of a solid ionic compound is formed from it’s gaseous ions under standard conditions.
Ca2+g + 2Cl-g –> CaCl2s
- exothermic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Lattice enthalpy of dissociation

A

The enthalpy change when 1 MOLE of solid ionic compound is dissociated into it’s gaseous ions under standard conditions.
CaCl2s –> Ca2+ + 2Cl-g

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Enthalpy change of dissociation

A

The enthalpy when 1 mole of bonds of the same type of molecule in the gaseous state is broken
F2g –> 2Fg

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Enthalpy change of 1st ionisation energy

A

The enthalpy change of when 1 mole of gaseous 1+ ions are made from 1 mole of gaseous atoms
- endothermic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Enthalpy change of atomisation

A

The enthalpy change when 1 mole of gaseous atoms are made from an element in it’s standard state.
1/2F2(g) –> F(g)
- endothermic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Enthalpy change of 2nd ionisation

A

The enthalpy change when 1 mole of gaseous 2+ ions are made from 1 mole of gaseous 1+ ions.
Ca+(g) –> Ca2+
- endothermic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

1st electron affinity

A

The enthalpy change when 1 mole of gaseous atoms form 1 mole of gaseous 1- ions.
e.g. O(g) –> O-(g)
- exothermic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why do we use Born Haber cycles?

A

Born-Haber cycles are useful to calculate lattice enthalpies. This is because we can’t calculate directly from experiments.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

2nd electron affinity

A
  • The enthalpy change when 1 mole of gaseous 1- ions form 1 mole of gaseous 2- ions.
    e.g. O-(g) –> O2-(g)
    -endothermic
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Why may the theoretical Lattice enthalpies and experiment Lattice enthalpies differ?

A
  • The covalent character of the ionic compound ( the amount at which the positive ions polarise the negative ions)
  • can result in greater experimental values for lattice enthalpy than theoretical ( when there is high covalent character)
  • The larger the ion the greater the distortion
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Theoretical Lattice Enthalpies and Experimental Lattice Enthalpies

A
  • Theoretical lattice enthalpies can be calculated from data assuming a perfectly ionic model.
  • during experimental testing you will find that you will not get the exact value you get from the theoretical lattice enthalpies
  • This means that the compound doesn’t follow the perfectly ionic model and has some covalent characteristics.
  • Most of the time the positive ion distorts the charge distribution in the negative ion. ( The positive ion polarises the negative ion + the more polarisation the greater the covalent character)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Enthalpy change of solution

A

The enthalpy change when 1 mole of an ionic substance is dissolved in the minimum amount of solvent to ensure NO FURTHER enthalpy change is observed upon further dilution.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

For a Substance to dissolve… (enthalpy change of solution)

A
  1. substance bonds must break (endothermic)
  2. New bonds formed between the solvent and substance (exothermic)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why may an ionic compound not dissolve?

A

For an ionic compound to dissolve the new bonds formed during the hydration of the freely moving ions must be equivalent or greater in strength than the ionic bonds broken.
- If not then substance is unlikely to dissolve

20
Q

How do you calculate the enthalpy change of solution

A
  1. using lattice dissociation enthalpy
  2. using enthalpy of hydration
    (use the hess’ law structure)
    The sum of the two is equal to the enthalpy of solution.
21
Q

Enthalpy of Hydration

A
  • Enthalpy change when 1 mole of aqueous ions is made from 1 mole of gaseous ions. / Enthalpy change when 1 mole of gaseous ions form 1 mole of aqueous ions.
    (exothermic)
22
Q

Define Entropy

A

Entropy is the measure of disorder in a system.
The more disorder there is the higher the level of entropy

23
Q

things to remember when calculating gibbs free energy

A
  • when calculating D S make sure it’s S = products - reactants and that you include balancing numbers in calculation
  • making sure you convert your entropy value from JK-1mol-1 to KJK-1mol-1 ( or you can convert your enthalpy to KJmol-1 but former is easier)
  • making sure your temperature is in KELVIN ( it’s not temp change so it matters that it’s kelvin)
24
Q

Why may endothermic reactions still be spontaneous?

A
  • a calculated positive entropy can tell you a reaction is feasible
  • increasing entropy is energetically favourable and some reactions that are enthalpically unfavourable (endothermic) can still spontaneously (feasibly) react if changes in entropy overcome changes in enthalpy
25
Q

Why may a reaction be theoretically feasible but not have a spontaneous reaction?

A
  • the reaction may be feasible but not spontaneous
  • This could mean it has a high activation energy or it’s an incredibly slow reaction.
26
Q

When is a reaction feasible?

A

When Delta G </ 0
- Temperature effects feasibility of a reaction
- this is dependent on whether delta H or delta S is positive or negative

27
Q

Why does the rate of reaction change when temperature changes, explain in terms of the rate constant.

A
  • the rate constant is fixed at particular temperatures. If the temperature changes the rate constant also changes.
  • As we increase the temperature the particles have more energy and they collide more often. This increases the rate.
28
Q

when calculating the rate constant what is important to remember?

A
  • finding the orders of reaction
  • calculating the units using the concentrations.
29
Q

rate equations

A
  • rate equations can only be constructed by conducting an experiment.
  • ## the initial rates can be used to work out the rate equation for a reaction.
30
Q

Iodine Clock Experiment

A

H2O2(aq) + 2H+(aq) + 2I- –> 2H2O(l) + I2(aq)
- in this practical you are looking for colour changes
- add sodium thiosulfate and starch (which acts as an indicator)
- the sodium thiosulfate reacts immediatley with the I2
- when there is no more sodium thiosulfate the I2 reacts with starch, resulting in a deep blue/black colour.

31
Q

Other methods of calculating the rate of an experiment

A
32
Q

Colorimeter

A
  • measures the absorbance of light by a coloured sample. The more concentrated a sample is, the darker it’s colour and hence the more light absorbed.
  • good for any reaction with a colour change.
33
Q

Rate-Concentration Graphs VS Concentration-Time Graphs

A

Rate-Concentration graphs
- help us identify the order
- the rate on a STRAIGHT HORIZONTAL LINE GRAPH is constant so the reactants are ZERO ORDER. (the change in concentration is not affecting the rate)
- the r ate on a straight DIAGONAL line shows a proportional relationship so FIRST ORDER.
- the rate on a curved line shows shows a SECOND ORDER reactant(s)

CONCENTRATION-TIME
- concentration on a straight diagonal line shows the reactant to be ZERO ORDER
- the concentration on a curved but moderately steep line is FIRST ORDER (more working out will likely be needed)
- the concentration on a STEEPLY curved line would be SECOND ORDER.

34
Q

Rate-determining step

A

the SLOWEST step in a MULTI-STEP reaction.
- speeding up the slowest step will increase the whole reaction rate.
- substances not in the rate equation won’t be in the rate determining step. THUS all substances in the rate determining step are IN the rate equation.
- catalysts can also be within rate equations
- for rate determining step reactants their rate equation power is their balancing number.
- The reactants that form the reactants in the rate determining step must also be apart of the rate equation.

35
Q

How can we determine the likeliness of a mechanism using the rate determining step?

A
  • when determining which mechanism is more likely to occur for a reaction you can look at the rate equation.
  • If certain molecules/reactants that are within the rate equation (including their balancing numbers shown as powers) show up in one of the mechanisms then that mechanism is more likely to occur.
36
Q

Arrhenius Equation

A
  • can be used to find activation when plotting
37
Q

Define overall order of reaction

A

The sum of the powers in a rate equation

38
Q
A
39
Q

suggest why hydration of chloride ions is an exothermic process

A
  • The water is polar
  • the chloride ions attract the slightly positive hydorgen
40
Q

The bond dissociation enthalpy

A

mean enthalpy change when one mole of covalent bonds is broken into 2 gaseous atoms
- this is averaged over different compounds of ranging energies

41
Q

the change enthalpy of atomisation

A

enthalpy change when one mole of gaseous atom is formed from the/an element in its standard state

42
Q

the enthalpy change of formation

A

the enthalpy change when one mole of substance is formed from its constituent elements in their standard states under standard conditions

43
Q

lattice dissociation enthalpy

A

enthalpy change when one mole of ionic crystal is broken into its constituents gaseous ions

44
Q

enthalpy change of hydration

A

enthalpy change when one mole of gaseous ions become aqueous ions

45
Q

what is lattice enthalpy dependent on?

A
  • the size of the ion
  • the charge of the ion

Alevel Chemistry (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions