cap 4 - organic chemistry and reaction rates

Question 1

why is carbon able to form such a diverse range of compounds?

Answer 1

2, 4 electron configuration (4 valence) ⇒ ability to covalently form 4 more single bonds ⇒ variety of arrangements (single, double, triple) ⇒ forms many compounds

Question 2

hydrocarbons

Answer 2

organic compounds, based on hydrogen and carbon atoms

Question 3

aliphatic

Answer 3

carbon atoms arranged in open chains ⇒ can be saturated or unsaturated

Question 4

aromatic

Answer 4

carbon atoms arranged in closed rings

Question 5

functional groups

Answer 5

atom or group of atoms responsible for typical chemical reactions, determining patterns of reactivity

Question 6

homologous series

Answer 6

group of molecules with same functional group, but different number of carbons in the main chain

Question 7

alkanes

Answer 7

single bonds only
saturated compounds
C(n)H(2n+2)

Question 8

alkenes

Answer 8

at least one double bond
unsaturated compound
C(n)H(2n)

Question 9

benzenes

Answer 9

unsaturated hydrocarbon of a perfectly hexagonal, flat ring structure consisting of 3 double and single bonds (rapid equilibrium model), and a cloud of delocalised electrons above and below the ring; colourless liquid at room temp

Question 10

formula for cycloalkanes

Answer 10

C(n)H(2n)

Question 11

formula for cycloalkenes

Answer 11

C(n)H(2n-2)

Question 12

saturated hydrocarbons

Answer 12

consisting of only single bonds (bonded to the maximum number of hydrogens)

Question 13

unsaturated hydrocarbons

Answer 13

consisting of at least one double or triple bond, thus being more reactive (double bond broken to accommodate addition of more hydrogen atoms)

Question 14

isomerism

Answer 14

same molecular formula but a different spatial arrangement (structural or geometrical)

Question 15

structural isomerism

Answer 15

varying physical structure (can be chain, positional, functional group)

Question 16

chain isomerism

Answer 16

consisting of branches and additional substituents

Question 17

substituents

Answer 17

additional “branches” or “stems”, named as according to where they are and how many carbons they have

Question 18

positional isomerism

Answer 18

location of double bonds

Question 19

functional group isomerism

Answer 19

location of functional groups

Question 20

geometrical isomerism (cis-trans)

Answer 20

structural rotations around C-C double bonds

Question 21

sigma bonds

Answer 21

• single bonds, strongest out of all bonds
• rotational symmetry (NO geometrical isomerism)

Question 22

pi bonds

Answer 22

• double or triple bonds
• weaker and more reactive
  
  • rotation causes weaker bond to “snap” or break
  • has different symmetry (geometric isomerism)
• much more electron deficient ⇒ much more susceptible to reactions

Question 23

reactivity of hydrocarbons

Answer 23

unsaturated hydrocarbons are MORE reactive than saturated hydrocarbons;

for alkanes to react, highly stable sigma bonds must be broken (requiring large amounts of energy to break the stronger bonds) ⇒ large input energy ⇒ relatively higher activation energy ⇒ lower rate of reaction ⇒ lower reactivity

Question 24

substitution reactions

Answer 24

type of chemical reaction where an atom or functional group of a molecule is replaced by another atom or functional group

Question 25

substitution of alkanes (energy)

Answer 25

UV light supplies sufficient energy to meet the activation energy of the reaction => breaking bonds between halogens (diatomic molecules) => atoms in high energy state can react with alkane to substitute with hydrogen

Question 26

substitution of benzenes (catalyst)

Answer 26

halogens involved in substitution aren’t electrophilic enough to break the aromatic nature of benzene, so a catalyst is used to attract electrons for substitution e.g. nickel catalyst for hydrogenation

Question 27

addition reaction

Answer 27

type of chemical reaction where atoms are added across the double bond of an alkene to form an alkane or a substituted alkane, breaking pi bond to form another sigma bond

Question 28

why do addition reactions happen so quickly

Answer 28

sigma is stronger and more energetically favourable to form, being more stable, so weaker pi bond will more readily break to form a stabler sigma bond

Question 29

test for unsaturation

Answer 29

add few drops of bromine water (orange) or iodine water (brown) into the tested liquid, and shake two layers would form, since nonpolar hydrocarbons are insoluble in the polar solution (halogens bottom layer) if unsaturated, would undergo addition reaction and decolorise

Question 30

complete combustion reactions

Answer 30

hydrocarbon + excess oxygen → carbon dioxide + water + energy

Question 31

incomplete combustion reactions

Answer 31

hydrocarbon + insufficient oxygen → carbon monoxide + water + energy hydrocarbon + insufficient oxygen → carbon + water + energy less exothermic than complete combustion, i.e. releasing lots of energy per unit; soot is air pollution, carbon monoxide is poisonous gas

Question 32

pressure

Answer 32

force exerted per unit area by collisions between gas particles and interior surfaces of container (gases consist of particles in constant random motion), measured in pascals (Pa)

Question 33

temperature

Answer 33

measure of average molecular kinetic energy

Question 34

activation energy

Answer 34

minimum amount of energy required for particles to react minimum amount of energy required to form the activation complex (energy needed for the bonds of the reactants to break)

Question 35

transition state (activation complex)

Answer 35

state corresponding to the highest potential energy (particular configuration) along the reaction coordinate activation complex = temporary, highly unstable formation (bonds of reactants broken, bonds of products not yet formed)

Question 36

collision theory

Answer 36

- reactants must collide - with sufficient, activation energy - at appropriate orientation

Question 37

rate of reaction depends on

Answer 37

- frequency of collisions - proportion of successful collisions

Question 38

rate of reaction

Answer 38

NUMBER OF SUCCESSFUL COLLISIONS OVER A GIVEN TIME change in concentration of reactants or products per unit time (speed of reaction) measured using indicators of reactions (mass, colour, volume, pH, concentration) => volume of gas produced, loss of mass, change in transparency slows over time (concentration of reactants decreases, reduced frequency of collisions)

Question 39

key factors for rate of reaction

Answer 39

temperature surface area volume / pressure presence of catalysts concentration

Question 40

concentration of dissolved reactants

Answer 40

higher concentration ⇒ more particles in the same amount of space ⇒ increased frequency of collisions, same proportion of collisions that are successful ⇒ more successful collisions (same chance but more collisions)

Question 41

pressure of gaseous reactants (volume of container)

Answer 41

decreased volume, increased pressure ⇒ smaller space for gas particles, closer together ⇒ increased frequency of collisions, same proportion of collisions that are successful ⇒ more successful collisions (same chance but more collisions)

Question 42

surface area of solid reactants

Answer 42

(all reactions with solids occur on the surface) split into several pieces ⇒ increased surface area ⇒ increased area for reactants particles to collide with ⇒ increased frequency of collisions, same proportion of collisions that are successful ⇒ more successful collisions (same chance but more collisions)

Question 43

temperature

Answer 43

higher temperature ⇒ higher average kinetic energy of particles increased average velocity of particles ⇒ increased frequency of collisions ⇒ more successful collisions (same chance but more collisions) colliding with more energy (increased number of collisions having sufficient activation energy) ⇒ increased proportion of collisions that are successful

Question 44

catalyst

Answer 44

a substance that speeds up a chemical reaction without being consumedz

Question 45

presence of a catalyst

Answer 45

offers an alternate pathway for the reaction with a lower activation energy, without directly lowering the activation energy greater proportion of collisions have sufficient energy to overcome activation energy and form transition complex ⇒ greater proportion of successful collisions

Question 46

maxwell-boltzmann distribution curve

Answer 46

demonstrates the proportion of particles that are expected to successfully undergo a collision and thus a chemical reaction

Question 47

sources of error for gas experiment (inverted cylinder)

Answer 47

(random) state of subdivision and surface area : volume ratio of marble chips (random) parallax error in reading inverted measuring cylinder (systematic) loss of gas produced; systematic delay of placing stopper (systematic) loss of gas by dissolution in water

Question 48

sources of error for "cross" concentration experiment

Answer 48

(random) parallax error, dependent on perception, to determine when cross disappears (systematic) “degree” of swirling, where agitation increases frequency of collisions (systematic) human reaction time

Question 49

sources of error for the "cross" temperature experiment

Answer 49

(random) parallax error, dependent on perception, to determine when cross disappears (systematic) “degree” of swirling, where agitation increases frequency of collisions (systematic) calibration of the water bath, assuming exact temperature of thermometer (systematic) temperature lost to surrounds (systematic) human reaction time