AQA GCSE Chemistry Paper 2

How do you measure the rate of a reaction?

By measuring the quantity of a reactant used or the quantity of product formed over time

What is the equation for calculating the mean rate of a reaction by measuring the amount of reactant used?

Mean rate of reaction = quantity of reactant used/time taken

What is the equation for calculating the mean rate of a reaction by measuring the amount of product formed?

Mean rate of reaction = quantity of product formed/time taken

What units can you measure the rate of a reaction in?

g/s or cm3/s or mol/s

How do you calculate the rate of a reaction at a specific time from graph of the quantity of reactant used or the quantity of product formed?

By measuring the gradient of a tangent drawn at that specific time on the graph

What are the five factors that can affect the rate of a reaction?

Concentration of reactants in solution, pressure of reacting gases, surface area of solid reactants, temperature and the presence of a catalyst

What theory can we use to explain how various factors affect the rate of a reaction?

Collision theory

What is collision theory?

Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy

What is the activation energy of a reaction?

The minimum amount of energy that particles must have to react

According to collision theory why does increasing concentration of reactant in solution increase the rate of the reaction?

It increases the frequency of collisions and so increases the rate of reaction

According to collision theory why does increasing the pressure of reacting gases increase the rate of the reaction?

It increases the frequency of collisions and so increases the rate of reaction

According to collision theory why does increasing the surface area of solid reactants in solution increase the rate of the reaction?

It increases the frequency of collisions and so increases the rate of reaction

According to collision theory why does increasing temperature increase the rate of the reaction?

It increases the frequency of collisions and makes the collision more energetic and so increases the rate of reaction

How do you increase the surface area of a solid reactant?

Grind it into a powder that has smaller particle size

What effect does increasing the temperature of a reaction by 10°C have on the rate of a reaction?

It doubles it

What is a catalyst?

A chemical that changes the rate of a chemical reaction but is not used up in the reaction

How do catalysts increase the rate of a reaction?

By providing a different pathway for the reaction that has a lower activation energy

How do you know in a reaction that a chemical is used in a reaction is a catalyst?

It is not included in the chemical equation for the reaction

What is a reversible reaction?

Where the products of a chemical reaction can react to produce the original reactants

What is the symbol used in reversible reaction equations that shows that the reaction is reversible?

How can you change the direction of a reversible reaction?

By changing the conditions; for example heating or cooling the reaction

Describe the energy changes in a reversible reaction

One direction will be exothermic and the other direction endothermic

When is equilibrium in a reversible reaction achieved in apparatus which prevents the escape of reactants and products?

When the rate of the forward and reverse reactions occur at exactly the same rate

What affects the relative amount of all the reactants and products at equilibrium in a reversible reaction?

The conditions

What happens to an equilibrium if any of the conditions change?

The system responds to counteract the change

What does Le Chatelier's principle predict?

The effects of changing conditions on a system at equilibrium

What affect will changing the concentration of one of the reactants in a reversible reaction have on the equilibrium?

The system will no longer be in equilibrium and the concentration of all the substances will change until equilibrium is reached again

What happens when the concentration of a reactant is increased in a reversible reaction?

More products will be formed until equilibrium is reached again

What happens when the concentration of a product is decreased in a reversible reaction?

More reactant will react until equilibrium is reached again

What happens when the temperature of a system in equilibrium is increased?

The relative amount of products at equilibrium increases for an endothermic reaction OR The relative amount of products at equilibrium decreases for an exothermic reaction

What happens when the temperature of a system in equilibrium is decreased?

The relative amount of products at equilibrium decreases for an endothermic reaction OR The relative amount of products at equilibrium increases for an exothermic reaction

What happens in gaseous reactions when the pressure of a system in equilibrium is increased?

The equilibrium position shifts towards the side with the smaller number of molecules as shown by the symbol equation for the reaction

What happens in gaseous reactions when the pressure of a system in equilibrium is decreased?

The equilibrium position shifts towards the side with the larger number of molecules as shown by the symbol equation for the reaction

Where is crude oil found?

In rocks

What is crude oil formed from?

The remains of an ancient biomass consisting mainly of plankton that was buried in mud

What chemically is crude oil?

A mixture of a large number of compounds; mainly hydrocarbons

What is a hydrocarbon?

A molecule made up of carbon and hydrogen only

What type of hydrocarbons are most of those found in crude oil?

Alkanes

What is the general formula of alkanes?

CnH2n + 2

What are the first four members of the homologous series of alkanes called?

Methane, ethane, propane and butane

What is a homologous series?

A family of organic compounds that have the same functional group, similar chemical properties and the same general formula

How can you separate crude oil into fractions?

By fractional distillation

What does each fraction of crude oil contain?

Molecules with a similar number of carbon atoms

What can we use each fraction of crude oil for?

As fuels or feedstocks for the petrochemical industry

Name five fuels produced from crude oil

Petrol, diesel, kerosene, heavy fuel oil and liquified petroleum gases

Name four useful materials produced by the petrochemical industry from crude oil fractions

Solvents, lubricants, polymers and detergents

Why are there such a vast range of natural and synthetic carbon compounds?

Because of carbon atoms' ability to form families of compounds

Describe the four steps involved in fractional distillation

Crude oil is heated to evaporate it and turn it into a vapour, the vapour rises through the column and cools, the vapours condense when they are cool enough, and liquids are removed from the column at different heights

What three properties of hydrocarbon change as the size of the molecule increase?

Boiling point, viscosity and flammability

How does the boiling point of a hydrocarbon change as its size increases?

It increases

How does the viscosity of a hydrocarbon change as its size increases?

It increases

How does the flammability of a hydrocarbon change as its size increases?

It decreases

Why are hydrocarbons good fuels?

Because during their combustion they release energy

What happens to the carbon and hydrogen in a hydrocarbon during combustion?

They are oxidised

What are the products of complete combustion of a hydrocarbon?

Carbon dioxide and water

What is the name of the process where hydrocarbons are broken down to produce smaller more useful molecules?

Cracking

Name the two types of cracking

Catalytic cracking and steam cracking

What are the conditions for catalytic cracking?

550°C using a zeolite catalyst containing aluminium oxide and silicon oxide

What are the conditions for steam cracking?

550°C and steam

What is always produced when an alkane undergoes cracking?

Smaller alkane molecule(s) and an alkene

Which is more reactive, an alkene or an alkane?

An alkene

How can you test for an alkene?

React it with bromine water

What do you observe when bromine water is mixed with an alkane?

There is no colour change; the bromine water remains orange/brown

What do you observe when bromine water is mixed with an alkene?

There is a colour change; the bromine water turns colourless

Why are alkanes cracked?

Because there is a high demand for fuels and some of the products of cracking are useful as fuels

What are alkenes used for?

To produce polymers and as starting materials to produce other chemicals

What are alkenes?

Hydrocarbons with a double carbon-carbon bond

What is the general formula of an alkene?

CnH2n

What do saturated hydrocarbons only contain?

Single bonds

Why are alkenes unsaturated hydrocarbons?

Because they contain two fewer hydrogen atoms that the alkane with the same number of carbon atoms

What are the names of the first four members of the homologous series of alkenes?

Ethene, propene, butene, pentene

What is the functional group in alkenes?

C=C

What determines the reactions of organic compounds?

The reactions of the functional group

How do alkenes react with oxygen?

They undergo incomplete combustion, burning in air typically with a smoky flame

How do alkenes react with hydrogen, water and the halogens?

By the addition of atoms across the carbon-carbon double bond so that the double bond becomes a single carbon-carbon bond

What conditions are required for alkenes to react with hydrogen?

Hydrogenation requires a catalyst

What conditions are required for alkenes to react with water?

Hydration requires the use of steam at 300°C and a catalyst

What conditions are required for alkenes to react with halogens?

None; the reaction is spontaneous

What is the functional group in alcohols?

-OH

What are the names of the first four members of the homologous series of alcohols?

Methanol, ethanol, propanol and butanol

What happens when ethanol reacts with sodium?

Bubbles of hydrogen gas are seen and sodium ethoxide is produced

C2H5OH + Na → H2 + C2H5ONa

What happens when alcohols burn in air?

They undergo complete combustion to form carbon dioxide and water

What happens when alcohols are added to water?

They dissolve; though solubility decreases as the molecules increases in size, so butanol is less soluble

What happens when alcohols react with an oxidising agent?

They are oxidised to carboxylic acids

How are aqueous solutions of ethanol produced?

By fermentation of sugar solutions using yeast

What is the word equation for the fermentation of sugar solution using yeast?

Glucose à Ethanol + Carbon Dioxide

What are the conditions for fermentation of sugar solution to produce ethanol?

Anaerobic conditions (absence of oxygen), 25-35°C

What is the functional group in carboxylic acids?

-COOH

What are the names of the first four members of the homologous series of carboxylic acids?

Methanoic acid, ethanoic acid, propanoic acid, butanoic acid

What happens when carboxylic acids react with metal carbonates?

React to form a salt, carbon dioxide and water

What happens when carboxylic acids are added to water?

They dissolve to form acidic solutions

What happens when carboxylic acids react with alcohols?

They form esters

Why are carboxylic acids weak rather than strong acids?

Carboxylic acids only partially ionise so do not contain as many hydrogen ions as strong acids (which fully ionise) so the pH is higher

What is the name of ester formed from ethanoic acid and ethanol?

Ethyl ethanoate

What are esters used for?

Solvents or because they have fruity smells

What is the word equation for the formation of esters?

Carboxylic acid + alcohol → ester + water

What is the name of the reaction that turns alkene into polymers?

Addition polymerisation

What happens in an addition polymerisation reaction?

Many small molecules (monomers) join together to form large molecules (polymers)

What is a repeating unit?

A part of a polymer that would make a complete polymer molecule if many of them were joined end to end