Aqa 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 speeds up 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; foe 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

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

The conditions

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

The system responds to counteract the change

HT What does Le Chatelier's principle predict?

If a change is made to an equilibrium, the equilibrium will act to oppose the change.

HT 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

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

More products will be formed until equilibrium is reached again

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

More reactant will react until equilibrium is reached again

HT 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

HT 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

HT 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

HT 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 is the scientific definition of a pure substance?

A single element or compound not mixed with another substance

What are the properties of pure substances?

Pure substances melt and boil at specific temperatures; this can be used to identify the pure substance

What is an everyday description of a pure substance?

A substance that has had nothing added to it, so it is unadulterated and in its natural state (such as milk)

What is a formulation?

A mixture designed as a useful product

How are formulations made?

By mixing the components in carefully measured quantities to ensure the product has the required properties

Give seven examples of formulations?

Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods

What is chromatography used for?

To separate mixtures

What can the results of chromatography be used for?

To identify substances

What are the two phases involved in chromatography?

Stationary phase, mobile phase

What does separation of substances depend upon in chromatography?

The distribution of substances between phases

What is the Rf value in chromatography?

The ratio of the distance moved by a compound to the distance moved by the solvent

What is the equation used to calculate the Rf value of a substance?

Rf = distance moved by substance/distance moved by solvent

How can the Rf value from chromatography be used to identify a substance?

Different compounds have different Rf values in different solvents and this can be used to identify the substance

How many spots would a pure substance produce during paper chromatography?

One

How many spots would a mixture of substances produce during paper chromatography?

More than one

What is the mobile phase in paper chromatography?

The solvent that moves through the paper carrying different substances with it

What is the stationary phase in paper chromatography?

Is contained in the paper and does not move through it

How does paper chromatography separate a mixture?

The different dissolved substances in the mixture are attracted to the two phases in different proportions causing them to move at different rates through the paper

What is the test for oxygen gas?

Insert a glowing splint into a test tube of oxygen and the splint will relight

What is the test for carbon dioxide gas?

Bubble carbon dioxide through an aqueous solution of calcium hydroxide (limewater) and the solution will turn milky (cloudy)

What is the test for chlorine gas?

Place damp red litmus paper into chlorine gas and it is bleached and turns white

What is the test for hydrogen gas?

Hold a burning splint at the open end of a test tube of the gas and hydrogen burns rapidly with a pop sound

For how long has the proportions of the different gases in the atmosphere remained much the same?

200 million years

What is the composition of today's atmosphere?

78% Nitrogen, 21% Oxygen, 0.9% Argon, 0.04 Carbon dioxide

Why do we not know the composition of the Earth's early atmosphere?

Evidence is limited because of the time scale of 4.6 billion years

What does one theory suggest formed the main atmosphere in the first billion years of the earth's existence?

Intense volcanic activity releasing carbon dioxide, water vapour and little or no oxygen into the atmosphere

What does one theory suggest the Earth's early atmosphere was like?

Mars' and Venus' atmospheres today

In addition to carbon dioxide and water vapour what other gases could have been produced by volcanic activity?

Nitrogen and small proportions of methane and ammonia

What caused the amount of nitrogen to gradually increase in the atmosphere?

Volcanic activity

What formed the oceans on the Earth?

Water vapour condensing as the Earth cooled

What processes led to the reduction of carbon dioxide in the atmosphere before life on Earth?

Used by plants and algae for photosynthesis, dissolved in the oceans and formed fossil fuels.

What caused the increase of oxygen in the Earth's atmosphere?

Plants and algae producing oxygen through photosynthesis

What is the word equation for photosynthesis?

Light - Carbon Dioxide + Water → Glucose + Oxygen

What is the symbol equation for photosynthesis?

6CO2 + 6H20-->C6H12O6 + 6O2

When did algae first start to produce oxygen on Earth?

2.7 billion year ago