AQA Combined science chemistry paper 2 higher

What is the equation for rate of reaction?

Mass / time
Vol/time
Mol/time

What factors can affect rate of reaction and how?

- Surface area- more particles exposed to reactants= greater chance of collision= rate increases .
- Temperature- Reactant particles have more energy= Move quicker= More collisions= Rate increases because particles have energy equal to/ greater than activation energy.
- Pressure/ concentration = More reactant particles per volume = crowded so greater chance of collision = rate increases.
- Catalyst= Reduces activation energy so rate increases.

What is a reaction vessel?

A container

Give an example of a catalyst

- Enzymes
- Iron
- Platinum
- Vanadium oxide

What is the collision theory?

The theory that chemical reactions only occur when reacting particles collide with eachother with sufficient energy.

What is the minimum ammount of energy that particles need to react called?

Activation energy.

What is the catalyst in a biological system?

Enzyme

On an energy graph, where would the reactants, activation energy, overall energy change and products be?

If reaction = exothermic are products below or above reactants

Products below reactants because they release energy rather than take in

If reaction= endothermic are products below or above the reactants?

Above reactants

What is a reversible reaction?

A reaction where the products can react together to form the original reactants

In a reversible reaction, what happens if one side is exothermic?

Other side is endothermic

What is dynamic equilibrium?

Equilibrium in a closed system that prevents escape of reactants and products where the reactions occur at exactly the same rate in each direction.

How can direction be changed of reversible reactions?

Due to changing conditions.

What is Le Chatelier's principle?

When a system at equilibrium has a change made to the conditions, it will respond to counteract that change.

What occurs during pressure increase if a system is at equilibrium?

Equilibrium moves to direction of fewer molecules of gas

What happens when concentration is changed to reactants or products at equilibrium?

- The system is no longer at equilibrium and the concentrations of all substances will change until equilibrium is reached again.

What is crude oil?

- A finite resource found in rocks
- Mixture of hydrocarbons.

Where does crude oil come from?

The remains of ancient biomass (mainly plankton) that was buried in mud.

What are hydrocarbons?

Alkanes. Contain only hydrogen and carbon.

What is the general formula for alkanes?

Cn H2n+2

What are the first 4 alkanes?

Methane, Ethane, Propane, Butane

How are hydrocarbons in crude oil seperated?

Into fractions using fractional distillation.

What can the fractions of fractional distillation produce?

- Fuels
- Feedstock for petrochemical industry

What fuels are produced from crude oil?

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

What useful materials are produced by the petrochemical industry?

Solvents, lubricants, polymers and detergents.

How does fractional distillation work?

- Hot crude oil enters near the bottom of a fractioning column, hot at bottom, cooler at top.
- Vapours from the oil rise through the column
- Vapours condense at boiling points.
- Liquids are led out of the column at different heights.

What is condensation?

Gas to liquid.

What is volatility?

How easily a compound evaporates

What is a fraction of crude oil?

A simpler more useful mixture containing hydrocarbons of similar length and similar boiling points.

What are short chain hydrocarbons?

Hydrocarbons with few carbon atoms

What are long chain hydrocarbons?

Hydrocarbons with lots of carbon atoms

What is fractional distillation?

The process of separating crude oil into groups of hydrocarbons with similar numbers of carbon atoms

What are the 3 stages of fractional distillation?

Evaporation, condensation, collection

Where is crude oil vapour put in a fractionating column?

At the bottom of the column and rises upwards

Short chain hydrocarbons have a _ boiling point

Low

What is the name for carbon containing compounds?

Organic compounds

What is the name for families of similar compounds containing carbon atoms?

Homologous series

What are the 2 changes in state that occur during fractional distillation?

Evaporation, condensation

Are short or long hydrocarbons more useful? Why?

Short. Cracking converts long hydrocarbins into short hydrocarbons. Less viscous and a lower boiling point,ignite easily and high volatility.

What is the word equation for complete combustion of a hydrocarbon?

hydrocarbon + oxygen --> carbon dioxide + water (+ energy)

During a combustion reaction, are the atoms in the hydrocarbon oxidised or reduced?

Oxidised

What is oxidation

Gain of oxygen

What are alkanes?

Saturated hydrocarbons that only contain single bonds

What are the fuels produced and uses from crude oil by fractional distillation?

Petrol, to run cars. Kerosene, to run planes. Diesel oil to run trucks. Heavy fuel oil, can be heating oil, fuel oil or lubricating oil.

What happens to the hydrocarbons as you go down the list? (methane, ethane, propane,butane.)

The size increases.

What is viscosity?

A liquid's resistance to flow, or thickness of fluid. High viscosity means it flows slowly, for example honey.

Describe the trend in viscosity in hydrocarbons., with reference to size.

As the size of the hydrocarbon molecules increases, the molecules get more viscous. So, long chain hydrocarbons flow more slowly, have a higher viscosity. Methane low viscosity, butane high.

What is flammability?

How easily a hydrocarbon combusts /burns.

Describe the trend in flammablity in hydrocarbons, with reference to size.

The flammability decreases. Short chain hydrocarbons are extremely flammable. Long chain hydrocarbons are hard to burn. As the size of the hydrocarbon molecules increases, the molecules get less flammable. Methane flammable, butane less flammable.

What can methane be used for due to its flammability?

A bunsen burner

What is boiling point?

The temperature where a liquid changes to a gas

What do all the first 4 alkanes have to do with eachother, referencing to boiling point?

All have a boiling point lower than room temperature, all are gases at room temperature.

Describe the trend in boiling point in hydrocarbons, referencing to size.

The boiling point increases as size increases. Long chain hydrocarbons have a high boiling point, hence why they condense at the bottom of the fraction. Methane lowest boiling point, butane highest.

In conclusion, what happens when the hydrocarbon size increases?

The viscosity increases, the boiling point increases and the flammability decreases.

Why do short chain hydrocarbons make good fuels? Reference to its properties.

They are highly flammable, have a low viscosity and a low boiling point.

What are alkanes and alkenes examples of ?

Homologous series of hydrocarbons

What does cracking mean?

Splitting up long chain hydrocarbons

Why do short chain hydrocarbons make good fuels?

They are flammable

What are most of the long chain alkane molecules produced from fractional distillation turned into?

Smaller, more useful alkane molecules by cracking.

What are the products of cracking used for ?

Fuels such as petrol for cars and paraffin for jet fuel.

What does cracking produce?

Alkanes and alkenes.

What is more reactive - alkanes or alkenes ?

Alkenes

What are alkenes used for?

To produce polymers and as starting materials to produce other chemicals

What is the test for alkenes?

Bromine water test

What colour is bromine water?

Bright orange

What happens when bromine water is added to an alkene?

The bromine reacts with the alkene to make a colourless compound, so the bromine water looses its colour.

What happens when bromine water is added to an alkane?

No reaction will happen and it will stay bright orange.

What are the two methods of cracking?

Catalytic cracking and steam cracking

What are the conditions for catalytic cracking?

- 550°C maximum temperature
- Use of a catalyst

What catalyst can be used for catalytic cracking?

- Aluminium oxide

What are the conditions for steam cracking?

- Over 880°C
-Steam
- No catalyst

What type of reaction is cracking?

Thermal decomposition

What is thermal decomposition?

The break down of molecules by heating them

Describe the process of catalytic cracking

The long chain hydrocarbon is heated to vaporize it, the vapor is then passed over the catalyst, the long chain molecules split apart on the surface of the catalyst.

Describe the process of steam cracking

The long chain hydrocarbon is heated to vaporize it, mixed with steam and heated to a very high temperature in order to split apart the long chain molecules

What are pure substances?

A single element or compound, not mixed with any other substance

How do you distinguish a pure substance?

- Pure substances will melt and boil at a fixed point, whereas mixtures will at a range of different temperatures

Is the diagram on the other side a mixture or pure substance?

Is the diagram on the other side a mixture or pure substance?

What is a formulation?

A mixture designed as a useful product

How is a formulation made?

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

Give some examples of formulations

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

What is chromatography?

A method used to separate the substances in a mixture

What is the method for chromatography?

See photo

What are the two phases of chromatography?

- Mobile phase: where the molecules can move (liquid or gas)
- Stationary phase: where molecules can't move (solid or really thick liquid)

What is formed between the two phases of chromatography?

An equilibrium because the substances constantly move between mobile and stationary phase

What chemicals will move further in chromatography?

The chemicals that spend more time in the mobile phase rather than the stationary phase

How many spots will a pure substance form on chromatography paper?

One spot, because only one substance in sample

What component is the stationary phase in paper chromatography?

The paper

What component is the mobile phase in paper chromatography?

The solvent, eg. water, ethanol

What determines the amount of time the molecules sped in each phase?

- How soluble they are in the solvent
- How attracted they are to the paper

What does soluble mean?

Ability to be dissolved in a solvent (water, ethanol)

What molecules will travel furthest in chromatography?

Molecules with a higher solubility and less attraction to the paper. Will spend more time in the mobile phase

What can the solvent front determine?

Distance traveled by solvent

Memorise this chromatogram

What is the Rf value formula?

distance travelled by substance / distance travelled by solvent

What is the distance travelled by the substance?

Distance from the baseline to the centre of the spot

How do you see if a certain substance is present in a mixture?

Run a pure sample of that substance alongside the mixture. If one of the spots of the mixtures match or if the Rf value is the same, the substance may be present

What happens if you change the solvent

The Rf value changes