DEVELOPING FUELS

What volume does 1 mole of gas always occupy at room temperature and pressure?

24.0dm³ (or 24000cm³)

What happens to temperature in exothermic reactions?

Increases

On an enthalpy level diagram, if something is high then whats its stability?

The higher something is the less stable

What is enthalpy? (in the most simple terms)

Stored heat energy

What are the units for enthalpy change?

KJmol^-1

What is the ideal gas equation?

pV = nRT

Standard enthalpy change of combustion=

Enthalpy change when 1 mole of a substance is completely combusted under standard condition

Standard enthalpy change of formation=

Enthalpy change when 1 mole of a substance is formed from its elements under standard condition

Standard enthalpy change of neutralisation=

Enthalpy change when 1 mole of H2O is formed when an acid and alkali react under standard condition

Standard enthalpy change of reaction=

The enthalpy change when the reaction occurs in molar quantities shown in the chemical equation, under standard condition.

Why is the enthalpy change in standard conditions?

It allows for comparison

What are the standard conditions?

298K / 100kPa / 1moldm^-3

Breaking bonds are…

Endothermic

Forming bonds are…

Exothermic

What is enthalpy change?

The heat energy transferred in a reaction at constant pressure (kJmol^-1)

Unit of pressure in the ideal gas equation

Pa

Unit of volume in the ideal gas equation

m³

Unit of temperature in the ideal gas equation

K / kelvin

What is ‘R‘ in the ideal gas equation?

Gas constant

3 ways of finding enthalpy change of reaction

Doing experiments / use Hess cycles / use bond enthalpy values

Does forming bonds make them become more or less stable?

More stable

What are the 2 main procedural problems of enthalpy change of combustion experiments?

Heat loss to surrounding / Incomplete combustion

What is the Hess’s law?

The enthalpy change is independent of the path taken

Why would a reaction be endothermic?

The E needed to break bonds is more than the E released from forming bonds

Describe an experiment they could use to determine the enthalpy change of combustion of liquid hexane in the laboratory (1 mark)

Burn the (known mass of) fuel under a container of (known volume of) water and measure the temperature increase of H2O

6 Ways to make basic experiment more accurate:

Use a lid / Use draught shield / Move calorimeter closer to flame / Use a bomb calorimeter / Stir to improve heat distribution / Use copper calorimeter instead of beaker

What is the empirical formula?

Simplest ratio of atoms in a molecule

What is the molecular formula?

Actual number of each type of atom in a molecule

A property of the molecular formula

No information about structure (ie don‘t show functional group)

What is the general formula?

Describes all member of a homologous series

Aliphatic

Does not contain a benzene ring

Aromatic

Contains a benzene ring

Arene

Contains a benzene ring

What is the functional group?

The part which reacts

All the bond angles (/shape) in saturated hydrocarbons are…

109.5 / tetrahedral

What are the 3 reactions alkanes can do?

Combustion / radical substitution with halogen / Cracking

What is the reason for cracking alkanes?

Long hydrocarbons are not useful, so we have to convert them into shorter, more useful products

What are the 2 types of cracking (in industry)?

Catalytic cracking / Steam cracking

Conditions for catalytic cracking in industry

500 degrees Celsius / zeolite catalyst

What is this practical?

Cracking in the lab

What is a catalyst?

Provides an alternative pathway with a lower Ea. Chemically unchanged at the end of the reaction.

What are homogeneous catalysts?

Catalysts and reactants are in the same state

What are heterogeneous catalysts?

Catalysts and reactants are in different states

Step 1 of heterogeneous catalysts reaction

The reactant molecules are adsorbed onto the catalyst surface weakening bonds within the reactants

Step 2 of heterogeneous catalysts reaction

Bonds within the reactant molecules break

Step 3 of heterogeneous catalysts reaction

New bonds form, making the product molecules

Step 4 of heterogeneous catalysts reaction

The product molecules leave the catalyst surface (desorption)

Write the chemical equation that happens in the catalytic converters in cars.

CO + NO —> CO₂ + 1/2N₂

How is CO formed in cars are why is it bad?

Incomplete combustion / its toxic

How is NO formed in cars are why is it bad?

N₂ and O₂ form the air react due to high temperature / respiratory irritant, causes photochemical smog and causes acid rain

(3) What elements are used as catalyst in cars

Pt / Rh / Pd

How can a catalyst be poisoned?

When other reactants adsorb strongly onto the surface and don’t react, blocking the surface and stopping the normal reactants from adsorbing.

What does ‘Adsorbed’ mean (in catalytic converters)

Form weak bonds with the surface (catalytic surface)

What are structural isomers?

Structural isomers have the same molecular formula but different structural formula

What are stereoisomers?

Stereoisomers have the same structural formula but different arrangement of atoms in space

What are the 2 criteria‘s for stereoisomerism (E/Z)

There must be a C=C as this restricts rotation / There must be 2 different groups on each C of the C=C

What are the 2 electrophilic addition reactions of alkenes with halogens?

Alkenes + X₂ —> Dihaloalkane / Alkenes + HX —> Haloalkane

What are the 2 electrophilic addition reactions of alkenes without halogens?

Alkene + H₂ —> Alkane / Alkene + H-OH —> Alcohol

What are the conditions for [Alkenes + X₂ —> Dihaloalkane]

RTP

What are the conditions for [Alkenes + HX —> Haloalkane]

RTP

What are the conditions for [Alkene + H₂ —> Alkane]

Nickle catalyst + high T&P / Platinum catalyst + RTP

What are the conditions for [Alkene + H-OH —> Alcohol]

H₂PO₄ catalyst + high T&P / conc. H₂SO₄ + steam

What are curly arrows for?

Curly arrows show the movement of e^-

Where can curly arrows start? (2)

From a lone pair / from the middle of a bond

What is this?

Mechanism for propene reacting with Cl₂

What is an electrophile?

A positive or partially positive species which forms a dative bond by accepting a pair of electrons

Test for proof for mechanism? (of ethene with bromine)

Add a solution of NaCl, only forms dibromoethane OR 1-bromo2-chloroethane (NEVER dichloroethane).

What does ‘sharing of pairs of electrons‘ suggest about the orbitals?

The orbitals are overlapping

What are the 2 types of overlap (of orbitals)?

End on overlap along the internuclear axis (sigma) / Sideways overlap of 2 parallel p orbitals above and below the internuclear axis (Pi)

A double bond is…

One sigma bond + One Pi bond

A triple bond is…

One sigma bond + Two Pi bonds

Source for CO₂

Complete combustion of fossil fuels

Source for CO

Incomplete combustion of fossil fuels

Source for NO / NO₂

N₂ and O₂ from the air react due to high temperatures in engine

Source for SO₂

From S impurities in fuels

Source for N₂O₄

Ploughing fertilized fields

Why is SO₂ a problem?

Causes acid rain (H₂SO₄)

Why is N₂O₄ a problem?

Respiratory irritant

Example for biofuel (/how its made)

Ethanol, which can be made from plants, by fermentation of their sugars. It is usually mixed with petrol

Advantages for biofuels (4)

Helps car engine perform well / carbon neutral / renewable / produces less CO

Disadvantages of biofuels

Needs a lot of land to grow the crops, which could otherwise be used to grow food / a lot of energy is needed for intensive cultivation of the crop

Shape and bond angles of alkanes

Tetrahedral, 109.5