chemistry paper 2

rate of a chemical reaction

how fast the reactants are changed into products

slow reactions

rusting of iron
chemical weathering

fast reactions

burning
explosions

rate of reaction graphs

steeper line \= faster rate
flat \= reaction finished
higher line \= more reactants and products

collision theory in rate of reaction

1. collision frequency of reacting particles
more collisions \= faster rate

2. energy transferred during a collision
particles need to collide with enough energy to be successful

factors affecting rate of reaction

1. temperature
particles have more energy, collide more frequently

2. concentration or pressure
more particles in an area \= more frequent collisions

3. surface area
smaller pieces \= more area for collisions to happen on

catalyst

a substance that speeds up the rate of reaction without being used up itself

catalyst's affect on rate of reaction

speed it up by decreasing activation energy

do this by creating an alternative reaction pathway with lower activation energy

e.g. enzyme

rate of reaction equation

amount of reactant used up or amount of product formed / time

precipitate

a solid formed in a reaction

precipitate and colour change showing rate of reaction

can observe how long it takes for a solution to lose or gain colour
can observe how long it takes a solution to become cloudy

change in mass showing rate of reaction

1. put reaction on scale
2. is a gas is produced, the mass will decrease
3. the quicker it decreases, the faster the reaction

volume of gas showing rate of reaction

gas syringe to measure vol of gas being produced
more gas given off in one time interval \= faster rate

finding reaction rates from graphs

1. calculating mean rate
overall change in y axis / total time taken

2. calculating rate at a point
draw a tangent at the point and find the gradient

reversible reaction

a + b ↔ c + d

rate of reversible reactions

as reactants react, their concentration falls. (forward reaction slows)
as products are made, their concentration rises
(backward reaction speeds up)

eventually forward reaction is at same rate as backward reaction (equilibrium)

equilibrium

both reactions are happening but there is no overall effect
unchanging balance of products and reactants
only occurs in a closed system

position of equilibrium

equilibrium doesn't mean amounts of reactants are equal
lies to left \= higher conc. of reactants
lies to right \= higher conc. of products

conditions affecting position of equilibrium

temperature
pressure (only in gases)
concentration of reactants and products

exothermic and endothermic reversible reactions

if endothermic in one direction, exothermic in other
energy transferred from surroundings \= energy transferred to surroundings

Le Chatelier's Principle

if you change the conditions of a reversible reaction at equilibrium, the system will try to counteract that change

changes to temperature

decrease temp \= equilibrium will more to exothermic direction to create more heat
vice versa for increase temp

changes to pressure

only for gases
increase pressure \= equilibrium moves to side with lower molecules of gas
vice versa for decrease pressure

changes to concentration

change concentration \= no more equilibrium
increase conc. of reactants \= makes more products
decrease conc. of products \= less reactants
etc

hydrocarbon

any compound formed from carbon and hydrogen only

alkane formula

Cn H2n+2

alkanes are saturated

each carbon bonds to four other atoms

homologous series

a series of compounds that have similar properties and the same general formula

saturated

bonded with the maximum amount of atoms

first alkane

methane CH4

second alkane

ethane C2H6

third alkane

propane C3H8

fourth alkane

butane C4H10

the shorter the hydrocarbon chain...

the less viscous
the more volatile
the more flammable
lower boiling points

complete combustion

happens in excess of oxygen
releases lots of energy
C and H from the hydrocarbon are oxidised

complete combustion equation

hydrocarbon + oxygen \= carbon dioxide + water

crude oil

fossil fuel
formed from remains of plats and animals
remains turn to oil with time, temp, and pressure
non-renewable
finite
mixture of lots of different hydrocarbons

fractional distillation

used to separate hydrocarbon fractions

uses of crude oil

fuel - kerosene, diesel etc
makes new compounds like polymers and solvents

cracking

splitting up hydrocarbons
turns long chain hydrocarbons into shorter chains

catalytic cracking

1. vaporise hydrocarbon
2. pass over hot powered aluminium oxide catalyst

steam cracking

1. vaporise hydrocarbon
2. mix with steam
3. heat to a very high temperature

thermal decomposition

breaking down molecules by heating them

cracking products

shorter chain hydrocarbon + alkene

alkene

hydrocarbons with a double bond between two carbons in their chain
two fewer hydrogens than alkanes

properties of alkenes

unsaturated
c\=c bond can open to bond to other atoms
much more reactive than alkanes

alkene formula

Cn H2n

first alkene

ethene C2H4

second alkene

propene C3H6

third alkene

butene C4H8

fourth alkene

pentene C5H10

incomplete combustion

combustion when there isn't enough oxygen in the air
smoky yellow flame
less energy released
happens in alkenes

incomplete combustion equation

alkene + oxygen \= carbon + carbon monoxide + water

functional group

group of atoms in a molecule that determine how that molecule typically reacts

alkane functional group

c-c

alkene functional group

c\=c

alcohol functional group

-OH

carboxylic acid functional group

-COOH

ester functional group

-COO-

alkene addition reaction

the c\=c double bond opens up, allowing a new atom to be added to each carbon

alkene + hydrogen

hydrogenation
hydrogen reacts with c\=c to form equivalent alkene
needs a catalyst
e.g. ethene + H2 \= ethane

alkene + steam

alcohol is formed
water added across double bond
needs a catalyst
e.g. ethene + steam \= ethanol

halogens + alkenes

addition reaction with halogen
each c\=c atom bonds with a halogen atom
e.g. bromine + ethene \= dibromethane

polymers

long chains of monomers (plastics)
normally carbon based
monomers normally alkenes

polymerisation

monomers becoming polymers
needs high pressure and a catalyst

addition polymers

made from unsaturated monomers
c\=c bond opens up to join to another opened up carbon atom
makes polymer chains
poly(name of monomer)

addition polymer diagram

alcohol general formula

Cn H2n+1 OH

first alcohol

methanol CH3OH

second alcohol

ethanol C2H5OH

third alcohol

propanol C3H7OH

fourth alcohol

butanol C4H9OH

alcohol properties

flammable
undergo complete combustion in air
first 4 alcohols soluble in water to make pH 7
react with sodium. 1 product is hydrogen
oxidised to produce carboxylic acids

alcohol uses

solvents because they dissolve things water can't
fuels e.g. spirit burners because they burn cleanly

fermentation

using an enzyme in yeast to convert sugars into ethanol

fermentation equation

fermentation conditions

fastest at 37ºc and in slightly acidic conditions
no oxygen

first carboxylic acid

methanoic acid HCOOH

second carboxylic acid

ethanoic acid CH3COOH

third carboxylic acid

propanoic acid C2H5COOH

fourth carboxylic acid

butanoic acid C3H7COOH

carboxylic acids + carbonates

\= salt + water + carbon dioxide

carboxylic acids properties

dissolve in water
dont ionise completely
weak acids (higher pH)

ester equation

alcohol and carboxylic acid
acid catalyst (e.g. sulfuric acid)

first ester

ethyl ethanoate CH3COOC2H5

condensation polymers

polymers containing different functional groups
monomers form bonds
e.g. polyester

molecule lost during condensation polymerisation

e.g. water

condensation polymer example

number of types of monomers

addition - one monomer type
condensation - two monomer types with diff func groups
or one monomer with 2 functional groups

number of products

addition - 1 product
condensation - 2 products

functional groups involved in polymerisation

addition - c\=c double bond
condensation - two reactive groups per monomer

amino acids

amino group + carboxyl group

amino acids form...

polymers called polypeptides via condensation polymerisation

long chains of polypeptides

proteins

natural occurring polymers

DNA
proteins
carbohydrate polymers (e.g. cellulose and starch)

What colour do lithium ions produce in a flame?

Crimson

What colour do sodium ions produce in a flame?

Yellow

What colour do potassium ions produce in a flame?

Lilac

What colour do calcium ions produce in a flame?

Orange-red

What colour do copper ions produce in a flame?

Green