Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

chemistry ocr b > df > Flashcards

df Flashcards

(59 cards)

Start Studying
1
Q

what is an exothermic reaction?

A

§energy is lost to surroundings (delta H reduces- negative value)

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

what is an endothermic reaction?

A

energy is taken from the surroundings to cool the reaction (delta H increases- positive)

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

what are standard conditions?

A

298k (25c) and 101kpa (1atm) 1moldm-3

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

equation for measuring enthalpy changes:

A

q=mcAT
kj=jg-1k-1 x g x k

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

what is the value for specific heat capacity?

A

4.18jg-1k-1

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

what is definition for standard enthalpy chance of COMBUSTION?

A

enthalpy change that occurs when one mole of substance is burnt completely in oxygen (done under standard conditions)

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

what is the definition for the standard enthalpy change of FORMATION?

A

enthalpy change when one mole of a compound is formed from its elements (down under standard conditions)

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

what is the standard enthalpy change of NEUTRALISATION?

A

measured using the amount of energy given out when acid reacts with alkali in aqueous solution

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

what is specific heat capacity?

A

the specific heat capacity of a substance is the amount of energy needed to raise the temperature of 1kg of substance by 1k

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

enthalpy change of combustion

A

reactants to products
co2 + h2o

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

enthalpy change of formation

A

reactants to products
each element involved

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

what is an aromatic compound?

A

compound that contain one or more benzene ring

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

what is an aliphatic compound?

A

compounds that do not contain benzene rings

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

what is the purpose of the functional group?

A

modifier thats responsible for there characteristics of the chemical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

define activation enthalpy

A

minimum amount of energy required for a reaction to take place

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

practical: What are the causes for less energy being transferred than expected when working out ΔH(c)

A

heat lost to surroundings
incomplete combustion of ‘alcohol’
evaporation of ‘alcohol’ from wick
not unde standard conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

define average bond enthalpy

A

energy required to break one mole of a specific type of bond in a gaseous molecule

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

what are properties of bond enthalpies?

A

energy is always required to break bonds
they’re always endo reactions
always have positive enthalpy value

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what kind of energy and enthalpy changes are bond formations?

A

exothermic
releases energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what kind of energy and enthalpy changes are bond breaking?

A

endothermic
absorbs energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

enthalpy change of combustion:
describe an experiment

A

1- measure 150cm3 of water using measuring cylinder and pour it into a beaker recording its initial temperature (nearest o.5c)
2- weigh the spirit burner containing ‘alcohol’
3-place spirit burner under the beaker and then light it - stir the water whilst whilst burning with the thermometer
4- after 3 mins extinguish the flame (placing cap over) then immediately record the maximum temp reached by water
5- re-weigh the spirit burner containing ‘alcohol’ (assume wick has not been burnt- decreases weight)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

suggest how to improve the experiment for determining enthalpy change of a reaction

A

add lid
add an insulating layer around beaker
use draft shield around apparatus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

calculating the enthalpy changes from average bond enthalpies

A

delta h = sum of bond enthalpies in reactants - sum of bond enthalpies in products

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

define the standard enthalpy change of reaction

Study These Flashcards
A

enthalpy change that accompanies a reaction in their molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states.

25
what makes an effective collision?
particles must have sufficient energy must collide in correct orientation
26
what factors can affect the rate of reaction?
concentration use of catalyst temperature pH
27
what effect does increasing temp have on a reaction?
increase rate as it increases the kinetic energy of the particles so they will have more frequent successful collisions
28
what effect does increasing pressure (g) / concentration have on rate of reaction?
it will increase rate more particles per unit of volume so more frequent successful collisions
29
what do catalysts do?
lowers the activation enthalpy of a reaction without undergoing any permanent changes itself (can be used multiple times)
30
properties of catalysts?
not used up in reaction provide a surface for a reaction to take place on they are regenerated at the end of reaction
31
what are the 2 types of catalysts?
homogeneous = same physical state as reactants heterogeneous = different physical state to reactants
32
how do homogenous catalysts interact with reactants?
they form an intermediate with reactants which then breaks down to give the product and regenerated catalyst
33
examples of homogeneous catalysts are:
sulphuric acid in the production of ester chlorine radicals in ozone depletion
34
how do heterogeneous catalysts interact with reactants?
they're usually solids in contact with gaseous reactants or reactants in solution act as surface for reaction to take place on
35
steps to reaction catalysed by a heterogenous catalyst?
1- reactants form bonds with atoms on the surface of the catalyst = ADSORBED 2- bonds in the reactants are weakened and break 3- new bonds form between the reactants to form the products 4- the bonds to the catalyst surface weaken and are broken releasing the products = DESORPTION
36
how are alkenes distinguished from other hydrocarbons?
by the presence of a carbon-carbon double bond implies its an unsaturated hydrocarbon
37
what happens when length if alkene change increases?
boiling point increases
38
what is the general formula of an alkene?
CnH2n
39
what prevents rotation in alkenes?
the pi bond locks the 2 carbon atoms into position
40
what are key features of C=C?
one sigma bond and one pi bond they are exposed and have high density vulnerable to attack by electrophiles (electron seeking species)
41
how are C=C formed in alkenes?
one sp2 orbital from each carbon overlap to form a single c-c (sigma = rotation can occur around this bond) the pi and is then formed by the two p orbitals which overlap each other sideways above and below the plane of the molecule
42
what is the arrangement of bonds around the C=C bond?
planar 120^
43
what is stereoisomerism?
have same structural formula but different spacial arrangement of atoms
44
2 types of stereoisomerism:
E-stereoisomers and Z-stereoisomers
45
how do stereoisomers occur?
there is restricted rotation around the C=C double bond there are two different atoms attached to both ends of the double bond
46
what are the Cahn-Ingold-Prelog rules for deciding E/Z isomerism?
higher atomic number is higher priority. Groups of higher priority on the same side of the double bond, then Z isomer.
47
effects of EZ stereoisomerism on physical properties:
Z = higher boiling point molecule will be polar due to the atoms being on the same side (one side will be slightly more negative and vice versa) intermolecular forces are both id-id (weakest IMF) and pd-pd E = lower boiling point molecule will be non-polar as bonds of different charges are on opposite sides dipoles cancel out intermolecular forces are only id-id (low bp)
48
what type of addition do alkenes undergo?
electrophilic addition and addition polymerisation (draw mechanism out on whiteboard)
49
what is the industrial importance of alkenes?
formation of polymers from ethene based monomers
50
alkanes: fractional distillation
oil is preheated then passed into he column the fractions condense at different temperatures temp of column decreases upwards separation depends on boiling points and size of molecules its a physical process involving the splitting of weak Van Der Waals forces
51
ho do you conduct fractional distillation in lab conditions?
1- heat flask wit bunsen burner or electric mantle 2- causes vapours of all components to be mixed 3- vapours pass up fractionating column 4- vapours of the substance with the lowest point reaches top of the fractionating column first 5- vapours of highest boiling points condense back into the flask 6- only the most volatile vapour passes into the condenser 7- condenser cools the vapours and condenses to a liquid an is collected
52
what is cracking?
conversion of large hydrocarbon chains into smaller hydrocarbons by breaking C-C bonds high Mr alkane => smaller Mr alkane + alkene + hydrogen
53
economic reasons for cracking:
petroleum fractions with shorter C chains are in high demand high demand for shorter hydrocarbons and so larger chains must be cracked products of cracking are more valuable then stating materials
54
what are the main types of cracking?
thermal and catalytic
55
conditions required for thermal cracking:
high pressure (7000kPa) high temperature (400-900)
56
conditions required for catalytic cracking:
slight or moderate pressure high temperature (450) zeolite catalyst
57
2 types of combustion:
complete = in excess oxygen alkanes burn incomplete = limited amount of oxygen (producing CO - TOXIC and/or C - sooty flame)
58
example of a complete combustion reaction?
C8H18 + 12.5O2 => 8CO2 + 9H2O
59
example of incomplete combustion reaction?
CH4 + 3/2O2 => CO + 2H2O

chemistry ocr b (32 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions