DF

Thermochemistry

the study of the energy and heat associated with chemical reactions

EXOthermic

gives out energy

ENDOthermic

takes in energy

Enthalpy Change

amount of energy transferred to and from the surroundings

negative enthalpy change

exothermic

positive enthalpy change

endothermic

What is enthalpy change affected by?

1. temperature

2. pressure

3. concentration

Standard Conditions

1. 298K (25 C)

2. 100kPa

3. 1 mol dm^-3

How to convert from Celsius to Kelvin?

add 273

Standard enthalpy change of reaction

The enthalpy change when molar quantities of reactants as stated in the equation react together under standard conditions.

specific heat capacity

The amount of energy needed to raise the temperature of 1 kg of substance by 1°C

q= mc/T

Standard enthalpy change of combustion

when one mole of substance in burned completely in oxygen under standard conditions in standard states

Standard enthalpy change of formation

when one mole of compound is formed from its elements under standard conditions in standard states

Standard enthalpy change of neutralisation

when one mole of hydrogen ions react with one mole of hydroxide ions under standard conditions and in solution containing 1 mol dm^-3

How is crude oil separated by fractional distillation?

Crude oil is heated to vaporise

Vapour passed into fractionating column

Top is cooler than bottom for negative temperature gradient

fractions separated by bpt so condense at different temperatures

Why does carbon form so many different structures?

• shares electrons to form stable covalent bonds

• Catenation.

• Forms 4 bonds, allowing endless shapes (straight, branched, rings)

• Easily bonds with other atoms for variety.

Catenation

the self-linking of atoms to form chains and rings

Hydrocarbons

compounds containing only hydrogen and carbon atoms

Aromatic compounds

contain benzene rings

Aliphatic compounds

do not contain benzene rings

Functional group

modifiers that are responsible for the characteristic chemical reactions of molecules

Alkanes

saturated hydrocarbons

general formula of Alkanes

C_nH_2n+2

Homologous series

a series of compounds in which all members have the same general formula

Structural isomer

compounds with the same molecular formula but different structural formula

general formula for an alkyl group

C_nH_2n+1

cycloaklanes general formula

C_nH_2n

How to name an alkane?

1. Location of side chain

2. comma

3. number of side chain (di, tri, tetra)

4. name of side chain

5. hyphen

6. name of longest chain

Properties of alkanes

1. n=1-4 are colourless gases in rtp

2. n=5-16 are colourless liquids

3. n=17+ are white waxy solids

Why are alkanes insoluble in water?

alkanes contain non-polar molecules

but water contains polar molecules which attract each other and prevent alkane molecules mixing with them

What is energy density?

The amount of energy released per unit mass of a fuel during combustion

How to calculate energy density

Energy density = Energy released during combustion ÷ Mass of fuel

Bond enthalpy

The energy required to break one mole of a bond in a gaseous molecule under standard conditions

Why is bond enthalpy always positive?

Because breaking bonds requires energy input

How do you calculate the energy change in a reaction using bond enthalpies?

∆H = ∑(Bond enthalpies of bonds broken) - ∑(Bond enthalpies of bonds formed)

What is the relationship between bond length and bond strength?

Shorter bonds are generally stronger than longer bonds

Why might bond enthalpy values differ from experimental results?

Bond enthalpies are averages over several compounds

Breaking bonds is

endothermic and requires energy

Making bonds is

exothermic and releases energy

Why is measuring enthalpy changes in reactions like combustion challenging?

Heat losses to the surroundings and incomplete combustion can affect the results

What is the significance of the table listing bond enthalpies?

It provides average values for different types of bonds

What is the role of fuel molecules in energy production?

Their chemical bonds store energy

What is the standard enthalpy change of combustion?

The enthalpy change when one mole of a substance burns completely in oxygen under standard conditions

What is the ideal gas equation?

pV = nRT

How do you calculate the volume of gas produced in a reaction?

Use the balanced chemical equation to find the moles of gas produced.

Multiply the moles by the molar gas volume at RTP (24 dm³ mol⁻¹)

How do you calculate the mass of gas from its volume?

Calculate the moles using moles = volume ÷ molar gas volume.

Use mass = moles × molar mass

What is the molar gas volume at standard temperature and pressure?

At STP

What are polymers

Polymers are large molecules made up of many smaller repeating units called monomers

What is addition polymerization

Addition polymerization involves the linking of monomers with a carbon-carbon double bond (alkenes)

What is condensation polymerization

Condensation polymerization involves the linking of monomers by eliminating small molecules such as water or hydrogen chloride

What is the difference between addition and condensation polymerization

Addition polymerization uses monomers with C=C bonds and produces no byproducts

What is poly(ethene)

a polymer made from ethene monomers and is widely used for making plastic bags and bottles

What is polychloroethene (PVC)

PVC is a polymer made from chloroethene monomers and is used for making pipes

What is poly(propene)

Poly(propene) is a polymer made from propene monomers and is used for making packaging

What is PTFE

PTFE (polytetrafluoroethene) is a polymer with high chemical resistance and non-stick properties

What are elastomers

Elastomers are polymers with elasticity

What are plastics

Plastics are synthetic polymers that can be molded into different shapes and have diverse applications

What are fibres

Fibres are polymers with high tensile strength and flexibility

What are the conditions for addition polymerisation

Addition polymerisation often requires high temperatures

What are the conditions for condensation polymerisation

Condensation polymerisation usually occurs at lower temperatures and may require a catalyst or acid/base conditions

Who developed nylon

Nylon was developed in the 1930s by Wallace Carothers and his team at DuPont

Why was the discovery of synthetic polymers significant

The discovery of synthetic polymers revolutionized industries by providing materials that are lightweight

What happens during addition polymerisation

The double bond in a monomer breaks to form a single bond. The monomers link together to form a long chain polymer

What is a repeating unit in a polymer

simplest sequence of atoms that repeats throughout the polymer chain

Properties of Polymers What determines the properties of a polymer

The properties of a polymer are determined by the type of monomers used

What are cross-linked polymers

Cross-linked polymers have covalent bonds between different polymer chains

What is ethene

Ethene (C₂H₄) is a simple alkene used as a monomer in addition polymerisation to make poly(ethene)

What is chloroethene

Chloroethene (C₂H₃Cl) is the monomer used to make poly(chloroethene) (PVC)

What is propene

Propene (C₃H₆) is a monomer used in addition polymerisation to make poly(propene)

What is tetrafluoroethene

Tetrafluoroethene (C₂F₄) is the monomer used to make PTFE

Why are synthetic polymers an environmental concern

Synthetic polymers are non-biodegradable and contribute to plastic pollution in the environment

How can polymer waste be managed

Polymer waste can be managed through recycling

What is an alkene?

unsaturated hydrocarbon

How are alkenes named?

1. Identify the longest chain and use the appropriate prefix to indicate the number of carbon atoms.

2. Follow the prefix with 'ene' to indicate the compound is an alkene.

3. For alkenes with longer chains or branched chains, indicate the position of the double bond using the lowest number possible.

4. For cyclic alkenes, use the prefix cyclo- (e.g., cyclohexene).

What is the general formula of alkenes?

CnH2n

what are electrophiles?

positive ion or molecule with partial positive charge that is attracted to a negatively charged region and will react by accepting a lone pair of electrons to form a covalent bond

What is electrophilic addition?

reaction where an electrophile reacts with an alkene's electron-rich double bond to form a single larger molecule

Describe the reaction of ethene with bromine.

1. Bromine becomes polarised as electrons are repelled by double bond

2. Bromine atom nearest double bond becomes slightly positive, the other slightly negative

3. 
   

How many pi/sigma bonds in a single bond?

1 sigma bond

sigma bonds form in

an area of increased electron density

How are sigma bonds formed?

overlap of s orbitals

What kind of bonds in a double bond?

one sigma

one pi

one pi bond consists of ___ areas of negative charge

one ______ one _________

2

above

below

What is cracking

process of breaking large hydrocarbon molecules into smaller ones

What is the purpose of cracking

To match the supply of long-chain hydrocarbons with the demand for shorter-chain hydrocarbons like petrol

What are the two main types of cracking

Thermal cracking and catalytic cracking

What are the conditions for thermal cracking

High temperature

high pressure

What is a free radical

A molecule or atom with an unpaired electron

What are the products of thermal cracking

Alkenes and sometimes smaller alkanes

What are the conditions for catalytic cracking

Lower temperatures (720 K) and pressures with a zeolite catalyst

What are the products of catalytic cracking

Branched alkanes

What is a catalyst

A substance that speeds up a chemical reaction by providing an alternative pathway with a lower activation energy

What are zeolites

Zeolites are minerals with a porous structure

Describe the stages of heterogeneous catalysis

1. Reactants get adsorbed onto the catalyst surface. Bonds are weakened.

2. Bonds in the reactants break.

3. New bonds form to create the products.

4. The second bond forms, and the product diffuses away from the catalyst surface, leaving it free to adsorb fresh reactants.

What is catalyst poisoning

when impurities bind to the surface of a catalyst and stop it functioning