Chemistry-OCR A-level DF

What is an endothermic reaction?

One which takes more energy in to break bonds, than it releases when new bonds are made.

What is an exothermic reaction?

One which releases more energy when new bonds are made than it takes in when reactant bonds are broken.

What are standard conditions?

298K, one atmosphere of pressure with substances in their standard states, and 1moldm-3 for solutions.

What are the units for specific heat capacity?

Jg^-1K^-1

What is the definition of the standard enthalpy change of combustion?

The enthalpy change that occurs when one mole of a substance is burnt completely in oxygen under standard conditions in standard states.

What is the sign of the enthalpy change of combustion and why?

Negative - it's an exothermic reaction.

What is the definition of the standard enthalpy change of formation?

The enthalpy change when one mole of a compound is formed from its elements under standard conditions under standard states.

What is the definition of standard enthalpy change of neutralisation?

The enthalpy change when one mole of hydrogen ions react with one mole of hydroxide ions to form one mole of water under standard conditions and in solutions containing 1moldm-3.

What is the ionic equation showing the formation of water?

H+ + OH- -> H2O

What is Hess' Law?

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

How do you calculate the enthalpy change of reaction?

Sum of the enthalpy changes of formation of the products - sum of enthalpy changes of formation of reactants.

What are aromatic compounds?

Compounds that contain one or more benzene rings.

What are aliphatic compounds?

Compounds that do not contain any benzene rings.

What is a functional group?

Modifiers that are responsible for the characteristic chemical reactions of molecules.

What is a hydrocarbon?

A compound that contains ONLY hydrogen and carbon atoms.

What is the chemical formula of nonane?

C9H20

What are structural isomers?

Compounds with the same molecular formula but different structural formula.

Name the structural isomer of butane?

2 methyl-propane

What is the formula of cyclohexane?

C6H12

What always forms the suffix of the name of a hydrocarbon?

The longest carbon chain

What is a saturated hydrocarbon?

A hydrocarbon that contains the maximum number of hydrogen atoms possible, with no C=C, or triple bonds.

What is meant by the term 'homologous series'?

A series of compounds in which all members have the same general molecular formula.

What do skeletal formula not contain?

Any of the letters for carbon or hydrogen atoms to represent C-H or C-C bonds.

What is meant by 'average bond enthalpy'?

The average amount of energy needed to break a particular bond.

What type of process is bond breaking?

Endothermic

What type of process is bond making?

Exothermic

What is meant by 'bond enthalpy'?

The energy needed to break one mole of a bond to give separate atoms in their gaseous state.

What is bond enthalpy measured in?

kJmol^-1

What is the relationship between bond enthalpy and bond length?

The shorter the bond, the stronger it is.

Why are triple bonds shorter than single bonds?

There are more electrons between the atoms being attracted to the positive nuclei.

Why do we measure bond enthalpies indirectly using enthalpy cycles?

There are often many types of bond in a compound; and hard to make measurements when everything is in the gaseous state.

What common errors are made during bond enthalpy calculations?

Forgetting that O2 has bonds that break; and forgetting that there are 2 double bonds in CO2, and 2 single bonds in H2O.

What is cracking?

A reaction in which a large molecule is made into smaller molecules

What is meant by the term 'unsaturated'?

Any organic compound that has a double or triple bond between carbon atoms.

What is a catalyst?

A substance which speeds up a reaction but can be recovered chemically unchanged at the end.

What is catalysis?

The process of speeding up a chemical reaction using a catalyst.

What is heterogeneous catalysis?

Where the reactants and catalyst are in different physical states.

What is the first stage of heterogeneous catalysis?

Reactant molecules are adsorbed onto the surface of the catalyst.

What is the final stage of heterogeneous catalysis?

Product molecules de-adsorb from the surface of the catalyst.

What is a catalyst poison?

A substance that stops a catalyst from functioning properly.

What is homogeneous catalysis?

Where the catalyst and reactant molecules are in the same physical state.

What 2 types of bond are present in alkenes?

Sigma, and Pi bonds

What does a reaction mechanism show?

The sequence of events in a reaction using the movement of electrons, represented by curly arrows.

What does a curly arrow show?

The movement of a pair of electrons.

What type of reaction is the reaction between bromine and ethene?

Electrophilic addition

What is an electrophile?

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

What is meant by bond polarisation?

When electrons in a bond are pushed along a molecule towards one end, making one end slightly positively charged, and the other end slightly negatively charged.

What is a carbocation?

An ion with a positively charged carbon atom.

What is an addition reaction?

A reaction where two or more molecules react to form a single larger molecule

Describe the test for alkenes?

Add bromine water - if a C=C bond is present, the bromine water will turn from orange to colourless

Name 2 possible products when butene reacts with hydrogen bromide?

1-bromobutane, or 2-bromobutane

What is formed when ethene reacts with steam at high temperature under high pressure?

Ethanol

What are the conditions for a hydrogenation reaction?

Platinum catalyst and standard conditions; or Nickel catalyst at 150oC and 5atm of pressure.

What are elastomers?

Polymers that are soft and springy, which then return to their original shape.

What is polymerisation?

When small molecules called monomers join together to produce long chain polymers.

How may products are there in addition polymerisation?

One

What is copolymerisation?

When more than one monomer is used in addition polymerisation.

What is the Avogadro constant?

(6.02 x 10^23) 6.02times10tothepower23

What is meant by the term molar volume?

The volume occupied by one mole of any gas at a particular temperature and pressure.

What is 1dm^3 in cm^3?

1000cm3

What is the molar volume of a gas at room temperature and pressure?

24dm^3

How many m^3 in a dm^3?

1 x 10^-3

What is the ideal gas equation?

PV = nRT (P=pressur in pa, V= volume in m^3, n=moles, R=constant(8.314)T=temperature in K)

What is volume measured in when using the ideal gas equation?

m^3

How many m^3 are 24dm^3?

0.0240m^3

What is the shape of a methane molecule?

Tetrahedron

What is chain isomerism?

An example of structural isomerism where the chains of a hydrocarbon are bonded in a different order.

What is stereoisomerism?

When the order of bonding is the same, but the arrangement of atoms in space is different.

What is position isomers?

When an atom, or group of atoms is substituted onto different places on a hydrocarbon chain.

What is functional group isomerism?

When molecules have the same molecular formula, but different functional groups.

What is E/Z isomerism an example of?

Stereoisomerism

What type of isomerism can But-2-ene exhibit?

E/Z isomerism

When substituents are on opposite sides of a double bond, what sort of isomer is it?

E (trans) isomer

What substituents are on the same side of a double bond, what sort of isomer is it?

Z (cis) isomer

How are prefixes listed in the general rule for naming alkanes, haloalkanes and alcohols?

Alphabetical order

What is evaporative emission?

When petrol, being so volatile gives off hydrocarbon fumes from the petrol tank and carburettor.

What is formed during incomplete combustion of fuels?

Carbon monoxide and carbon particulates.

What effect do carbon particulates have on the environment and people?

Cause of global dimming, can cause breathing difficulties in asthmatics.

How does sulphur dioxide get into the atmosphere?

Burning of sulphur impurities in fuels.

What effect does sulphur dioxide have on the environment?

It's a cause of acid rain.

What is photochemical smog?

When primary pollutants are acted upon by sunlight to produce secondary pollutants, which cause haziness and reduced visibility in the air.

How can we remove nitrogen oxides from the air?

Catalytic convertor

Name an alternative to fossil fuels?

Ethanol, biodiesel, hydrogen

What is a disadvantage of using hydrogen as a fuel?

Its production from water depends on the use of electricity (made in power stations).

What are fuel cells used for?

Generating electricity on a small scale in cars.