Chemistry Unit 2

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  • Created by: Stephen
  • Created on: 31-05-13 13:43
Name some examples of catalysts in industry (2)
*Iron in haber process. *Nickel in hydrogenation of margarine.
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How do catalysts help reduce energy consumption and help the environment? (3)
*Many industrial processes rely on catalysts as they reduce costs *As they lower the activation energy of a reaction less energy is needed to start the reaction, hence fewer energy costs. *With less energy needed fewer fossil fuels are burnt.
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Explain how a catalyst speeds up a reaction
Offers an alternate route for the reaction to follow, thus lowering the activation energy.
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What is a catalyst?
A substance that increases the rate of a chemical reaction, without being used in the process.
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Define the term "rate of reaction".
The rate of reaction is the change in concentration of a reactant or a product in a given time.
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What effect does pressure have on reaction rate? (2)
*Gaseous reactants act the san a smaller volume, therefore more collisions will occur.
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What effect does concentration have on rate of reaction? (3)
*More molecules in the same volume, therefore the likelihood of a collision is greater. *Collisions will be more frequent, more collisions will occur in a certain time. *The molecules will be closer together thus greater chance of collisions
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Define activation energy
The minimum energy required for a reaction to take place. by breaking bonds.
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What is enthalpy?
Enthalpy, H, is the heat content stored in a chemical system.
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How are polymers disposed? (2)
*Polymers cannot be burnt as they could release harmful pollutants. *Therefore, many plastic polymers are recycled, melted down and re-used. The polymers CANNOT be mixed.
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Define the term "biodegradable"
A material that is broken down naturally in the environment by living organisms.
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Why are polymers difficult to dispose of?
Polymers are non-biodegradable as they are so durable, this poses problems as they are filling up landfill sites and are harmful to the environment.
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Give uses of polystyrene
Foam packaging, Insulation, Food retail, Model-making
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What is a repeat unit?
A repeat unit is a specific arrangement of atoms the appears in the structure over and over again.
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What is an addition polymer? (2)
*An addition polymer is a very long molecular chain, formed by repeated addition reacts of many unsaturated alkenes (monomers) *Addition polymers have long saturated chains.
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What is radical polymerisation?
Radical polymerisation requires temperatures of 200 degrees Celsius and high pressure. This reaction can lead to branching of the polymer chain and the production of polymer mixtures such as polystyrene.
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What is the Ziegler-Natta process?
This process involves the usage of specialist catalysts such as TiCl3 and Al(C2H5)2Cl at 60 degrees. The alkene is passed over the catalyst to react, the process is slow and unreacted alkenes are recycled and passed over again.
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What is a polymer?
A long, saturated, molecular chain formed by repeat monomer units.
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What is a monomer?
A monomer is a small, unsaturated molecule that combines with other monomers to form a polymer.
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Name 3 chemicals made from ethene (3)
*Ethanoic acid, used in the production of vinegars *Etha-1,2-diol, anti-freeze and polyester. *1,2 Dichloroethane - paint remover, degreaser.
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What is ethene widely used for?
Polymerised and used to make many plastics
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What is a biofuel?
A biofuel is a fuel that is derived from recently living material, such as plants.
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What crops are grown specifically for energy? (2)
*Sugar cane *Rape
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How is ethanol made from plants?
Ethanol is made by fermenting sugar and other carbohydrates.
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Why is ethanol a significant alternate fuel?
When mixed with petroleum, ethanol is a significant alternate fuel as it burns well in a petrol engine, that does not need to be heavily modified, and it significantly reduces harmful emissions. It is also renewable.
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Explain how steam is used in the production of alcohols.
Steam and a gaseous alkene are reacted at a high temperature and pressure in the presence of a phosphoric acid catalyst. The process is sometimes called the hydration of an alkene.
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/What is electrophillic addition
A type of addtion reaction in which an electrophile is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond.
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Give an example of an addition reaction.
Alkene reaction with a polar molecule such as Br2 or H2
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In a C=C bond why does the pi bond react and not the sigma bond?
The pi bond is weaker than the sigma bond and so it is easier to break.
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How does branching effect the boiling point of alkanes?
The boiling point will be lower as there will be fewer points of contact, thus less van der waals' forces between each molecule. Therefore, less energy is needed to break the intermolecular bonds hence a lower boiling point.
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Explain how fractional distillation works. (2)
*Crude oil is vaporised and then passed through a fractionating column which is hotter at the bottom than the top. *When the oil gas reacts a level where a certain part of the gas has a lower boiling point than the level it will convert into a liquid
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What happens to the boiling point of an alkane as its chain length increases?
Boiling point will increase as there will be more points of contact between each molecules thus will have greater van der waals' forces between each molecule. Hence more energy needed to break intermolecular bonds, therefore higher boiling point.
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What is a substitution reaction?
A reaction where an atom, or a group of atoms, is replaced by another atom, or group of atoms.
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What is fractional distillation?
The separation of the components in a liquid mixture into fractions which differ in boiling points (and hence chemical composition).
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What is "cracking"?
The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes.
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Explain homolytic fission
The breaking of a bond where each atom gets one electron from the electron pair hence forming two radicals.
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Explain heterolytic fission
The breaking of a bond where one atom gets both bonded electrons, forming two ions.
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What is a funtional group?
A group of atoms in a molecule which determines its chemical reactivity.
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What is a structural formula?
The minimum amount of detail for the arrangement of atoms in a molecule
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Why is Crude oil important?
We have come to rely on crude oil as it is vital for fuels and indirectly is used in many other industries. However, the known deposits of crude oil are rapidly depleting.
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What problems arise from the use of Crude oil? (2)
*As stocks deplete, the price of crude oil is rising quickly. *Fuels, derived from crude oil, produce harmful pollutants which contribute to climate change when combusted.
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What factors alter the rate of a chemical reaction? (5)
*Temperature *Pressure (when *Concentration *Surface area *Use of catalysts
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What is Hess' law?
States that, if a reaction can take place by more than one route and the final conditions are the same, the total enthalpy change is the same for each route.
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Define bond enthalpy
The enthalpy change that takes place when breaking, by homolytic fission, one mole of a given bond in the molecules of a gaseous species.
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Formula for change in enthalpies when given bond enthalpies.
ΔH = (Sum of bond enthalpies of bonds broken) - (Sum of bond enthalpies of bonds formed)
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Suggest reasons why experimental values may differ from theoretical values.
Human error, errors in equipment (heat escaping into the environment from calorimeter)
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Define the standard enthalpy change of formation.
The enthalpy change that takes place when one mole of a substance is formed from its elements, under standard conditions and with reactants and products in their standard states.
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Define the standard enthalpy change of combustion
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, and with all reactants and products in their standard states.
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What are standard conditions and standard states? (2)
*100kPa (1 atmosphere), 1mol dm-3 (when reacting an aqueous solution), 298K (25 degrees C) *The physical state of a substance under standard conditions.
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What do the reactions that take place in photosynthesis and respiration have in common?
They are the opposite of one another. Whilst respiration is exothermic, photosynthesis needs energy from the sun to take place hence it is endothermic.
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Card 2

Front

How do catalysts help reduce energy consumption and help the environment? (3)

Back

*Many industrial processes rely on catalysts as they reduce costs *As they lower the activation energy of a reaction less energy is needed to start the reaction, hence fewer energy costs. *With less energy needed fewer fossil fuels are burnt.

Card 3

Front

Explain how a catalyst speeds up a reaction

Back

Preview of the front of card 3

Card 4

Front

What is a catalyst?

Back

Preview of the front of card 4

Card 5

Front

Define the term "rate of reaction".

Back

Preview of the front of card 5
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