Unit 5 Applied science level 3 BTEC Chemistry

chemical energy

the energy required to break or make bonds

exothermic reaction

A reaction that releases more energy in the form of heat

what is the enthalpy change of an exothermic reaction

negative

endothermic reaction

A reaction in which more energy is absorbed

what is the enthalpy charge of an endothermic reaction

positive

what will happen to the enthalpy diagrams when a catalyst is added

less activation energy will be required during this reaction

enthalpy change

the change n eat energy at a constant pressure

Enthalpy change of formation

when one mole of a compound is formed from its element under standard conditions

enthalpy change of combustion

when one mole of a substance is burnt in oxygen under standard conditions

enthalpy change of hydration

when one mole of a gaseous ion are dissolved in water to make an infinite dilute solution

what are the three standard conditions

temperature

concentration

pressure

what are the units for the three standard conditions

temperature- 298k

concentration- 1mol dm-3

pressure- 100kpa

what is the equation for enthalpy change

change in internal energy + pressure x change in value

how o you convert Celsius to kelvin

+ 273

What is a catalyst?

a substance that speeds up the rate of reaction by decreasing the activation energy needed for the reaction, so it provides the reaction with an alternate pathway. the catalyst is never used up throughout the reaction

What is Hess's Law?

The total enthalpy change of a reaction is independent of the route taken.

What is lattice energy?

the energy required to make one mole of an ionic lattice

what is the homologous series?

A group of chemicals that react in a similar way because they have the same functional group

what type of bond is an alkane?

single

what type of bond is an alkene?

Double

what type of bond is an alkyne

Tripple

what is the general equation for an alkane?

Cn2H2n+2

what is the general equation for an alkene?

Cn2H2n

what is the general equation for an alkyne?

Cn2H2n-2

what is the name given to a compound with one carbon chain

meth

what is the name given to a compound with two carbon chain

eth

what is the name given to a compound with three carbon chain

prop

what is the name given to a compound with four carbon chain

but

what is the name given to a compound with five carbon chain

pent

what is the name given to a compound with six carbon chain

hex

What is an isomer?

compounds with the same molecular formula but different structural formulas

What is chain isomerism?

When the hydrocarbon chain is arranged differently (such as branching).

what is a positional isomer?

that have the same carbon skeleton and the same functional groups but differ from each other in the location of the functional groups on or in the carbon chain.

what is a functional group isomer?

isomers that have the same molecular formula (that is, the same number of atoms of the same elements), but the atoms are connected in different ways so that the groupings are dissimilar

what is the bond angle of the C-H in a single bond?

109.5 degrees

What is the bond angle of the C-H in a double bond?

120 degrees

why are alkanes less reactive than alkenes?

Alkenes and alkynes are generally more reactive than alkanes due to the electron density available in their pi bonds. In particular, these molecules can participate in a variety of addition reactions and can be used in polymer formation

what are the four stages of free radical substitution?

1- initiation

2-propagation a

3-propagation b

4- termibation

what happens during initiation?

The Initiation stage is where free radicals are produced.

what occur at the stage of propagation?

this is when the radicals react and form different free radicals

What happens in termination?

the combination of the free radicals to form a stable product

What is hetrolytic bond fission?

when a convalent bond is broken, the shared pair of electrons is taken by one of the atoms

What is homolytic bond fission?

The even breaking of a bond, where each atom takes away one electron to form radicals.

what is a primary stucture?

when the there is only one CH3 added to the compound

what is a secondary structure

where there are 2 CH3 groups either side of the compound

What is tertiary structure?

where there is 3 CH3 groups branched of the central carbon chain

Why is a pi bond weaker than a sigma bond?

a pi bond requires less energy to be broken, the overlap of the atomic orbitals in the pi bond is a sideways overlap which is a weaker overlap in comparison to the sigma bond that is a head on overlap.

what type of reaction takes place between calcium hydroxide and hydrochloric acid?

neutralisation

what products are produced between an acid + base reaction?

salt and water

what products are produced between an acid and a metal

salt and hydrogen

What does amphoteric mean?

can act as an acid or a base

what products only discharge?

chloride

bromide

iodine

what is a diaphragm cell?

chloride ions are oxidized at the anode to produce chlorine, and at the cathode, water is split into caustic soda and hydrogen. The diaphragm prevents the reaction of the caustic soda with the chlorine. A diluted caustic brine leaves the cell.

what is a membrane cell?

is used to prevent the reaction between the chlorine and hydroxide ions.

what cell is better diaphragm or membrane?

membrane, despite it being more expensive, it requires less maintenance and provides a greater purity of sodium hydroxide

and less iceberg per tonne of chloride produced.

what charge is the anode?

positive

what charge is the electrode?

negative

what is the equation given for the reaction of chloride ions at the anode?

2CL- -> Cl2 +2e-

define aluminium?

durable, quite strong, lightweight, also cheap.

why is titanium better than aluminium?

it in more dense, stronger.

a much smaller volume of titanium is needed to produce a frame of similar strength to the aluminium.

why would aluminium be selected over titanium?

cost- 46 times more expensive per tone of titanium

would be chosen as the benefits are not offset by the extra cost.

what is the extraction of aluminium?

aluminium ore, bauxite, is mixed and then produced to form alumina, which is aluminium oxide. molten alumina is then electrolysis using the halt-heroult process.

what is titanium extraction?

done by using the kroll process, expensive due to the large amounts of energy needed to create the high temperatures involved.

batch process