Quizlet Flashcards
What is meant by the rate of chemical reactions
The speed at which reactants are made to products
How is the rate of reaction calculated
State the 5 factors affecting the rate of a chemical reaction
concentration of reactants pressure of gases surface area temperature catalysts
What is collision theory
Chemical reactions can occur only when reacting particles collide with eachother with sufficient energy
How does increasing the temperature effect the rate of reaction
the higher the temperature the faster the reaction As the temperature increases kinetic energy of the particles increases, also they move faster so they collide more frequently
How does concentration effect the rate of a reaction
If the concentration increases the reaction will be faster If there are more reactants there will be more frequent collisions
How does increasing the surface area increase the rate of reaction
If one of the reactants is a solid, then breaking it into smaller pieces will increase its surface area to volume ratio This means that for the same volume of the solid, the particles around it will have more area to work on - so there will be collisions more frequently
How does using a catalyst increase the speed of a reaction
They do this by decreasing the activation energy needed for the reaction to occur They do this by providing an alternative reaction pathway with a lower activation energy
What is a reversible reaction
When the products can react to form the reactants again
What will happen to the speed of the reaction as the reactants react
Their concentration fall so the forward reaction will slow down but as more and more products are made and thier rise, the backward reaction will speed up
What is equilibrium
The point at which the rates of the forward and backward reactions in a reversible reaction are the same, and so the amounts of reactants and products in the reaction container dont change
When is the only time that equilibrium can take place
If the reversible reaction takes place in a closed system which means that none of the reactants or products can escape and nothing else can get in
What does the position of equilibrium depend on
Temperature pressure concentration
How are reversible reactions affected by endo or exothermic reactions
In reversible reactions, if the reaction is endothermic in one direction it will be exothermic in the other The energy transferred from the surroundings by the endothermic reaction is equal to the energy transferred to the surroundings during the exothermic reaction
What le chateliers principle
The idea that if you change the conditions of a reversible reaction at equilibrium, the system will counteract the change It can be used to predict the effect of any changes you make to a reaction system
How do reversible reactions try to counteract changes to temperature
If you decrease the temperature, the equilibrium will move in the exothermic direction to produce more heat. This means you’ll get more products for the exothermic reaction and fewer products for the endothermic reaction. If you increase the temperature the equilibrium will move in the endothermic direction to try to decrease it. You’ll now get more products for the endothermic reaction and fewer products for the exothermic reaction.
How do reversible reactions try to counteract changes to pressure
Changing the pressure only affects the an equilibrium involving gases If you increase the pressure, the equilibrium tries to reduce it If you decrease the pressure, the equilibrium will try to increase it
How do reversible reactions try to counteract changes to concentration
If you change the concentration of either the reactants or the products, the system will no longer be at equilibrium. So the system responds to bring itself back to equilibrium again. If you increase the conc of the reactants, the system tries to decrease it by making more products and vice versa
What is a hydrocarbon
Any compound that is formed from carbon and hydrogen atoms only
What are alkanes and what are some of their properties
Alkanes are the simplest type of hydrocarbon you can get, they have the general formula CnHn+2 They are a homologous series they are saturated compounds
Methane
Ethane
Propane
Butane
Give some examples of how the properties of hydrocarbons change as the length of the hydrocarbons change
The shorter the chain: the more runny a hydrocarbon is, more volatile, more flammable, used as bottled gas for fuel
What happens during a complete combustion reaction and how are they used
both carbon and hydrogen from the hydrocarbon are oxidised hydrocarbons are used as fuels due to the amount of energy released when they combust completely
What is crude oil
Crude oil is a fossil fuel that is formed from the remains of plants and animals that died millions of years ago and were buried in mud
What are fossil fuels an example of
Non-renewable fuels, they take long to make and are being used up faster than they are being formed
What is crude oil a mixture of
Lots of different hydrocarbons most of which are alkanes
How are different compounds in crude oil seperated
fractional distillation
How does fractional distillation work
The oil is heated until most of it has turned to gas. the gas enters a fractionating columnThe longer hydrocarbons have higher boiling points so they condense back into liquid and drain out of the early on, when they are near the bottom. The shorter hydrocarbons have lower boiling points so they condense and drain out much later on, near to the top of the column where its coolerYou end up with the crude oil mixture seperated out into different fractions, each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms so they have similar boiling points
What is cracking
When hydrocarbons can be broken down to produce smaller, more useful molecules
What are the 2 types of cracking
catalytic cracking steam cracking
What are the products formed by cracking
Alkanes & alkenes
How does catalytic cracking work
Heat long chain hydrocarbons to vaporise them, vapour then passed over a hot powdered aluminium oxide catalyst The long chain molecules split apart on the surface of the specks of catalyst
How does steam cracking work
Vaporise them, mix them with steam and then heat them to a very high temperature
What are alkenes
Alkenes are hydrocarbons which have a double bond between 2 of the carbon atoms in their chain They are unsaturated
What is the general formula for alkenes
Ethene
Propene
Butene
Pentene
How do alkenes react most of the time
Addition reactions The carbon carbon double bond will open up will open up to leave a single bond and a new atom is added to each carbon
Addition reaction of hydrogen to an alkene
Hydrogen can react with the double bonded carbons to open up the double bond and form the equivalent, saturated alkane it reacts with hydrogen in the presence of a catalyst
How can steam react with alkenes to form alcohols
When alkenes react with steam, water is added across the double bond and an alcohol is formed Alcohol can be purified from the mixture by fractional distillation
How can halogens react with alkenes in addition reactions
They react with halogens such as bromine, chlorine and iodine, the molecules formed are saturated with the C=C carbons each becoming bonded to a halogen atom
How can the addition of bromine to a double bond be used to test for alkenes
When orange bromine water is added to a saturated compound like an alkane, no reaction will happen and it will stay bright orange whereas if its added to an alkene the bromine will add across the double bond, making a colourless dibromo-compound so the bromine water is decolourised
What are polymers
Polymers are long molecules formed when lots of small molecules called monomers join together which is called polymerisation
What 2 conditions is necessary for polymerisation
High pressure Presence of a catalyst
What are addition ploymers formed from
Unsaturated monomers, like alkenes
How do addition polymers form
The carbon carbon double bonds within the monomers break, and allow the two monomer molecules to bond to eachother
What is the general formula for alcohols
First 4 alcohols
What are the 4 properties of alcohols
They are flammable They are all soluble in water They react with sodium to form hydrogen They oxidise to form carboxylic acids
What are 4 things alcohols are used for
Alcoholic drinks Solvents Fuels
Why are alcohols used as solvents
They can dissolve lots of different substances, including hydrocarbons, oils and fats
What is the general word equation for the complete combustion of an alcohol
What is fermentation
The anaerobic respiration of sugars by yeast cells to produce ethanol and carbon dioxide
What is the word equation for the reaction of making ethanol by fermentation
First 4 carboxylic acids
How do carboxylic acids react with water
They dissolve in water but they dont completely ionise This means they form weak acidic solutions Which gives them a relatively high pH for an acid
How do carboxylic acids react with carbonates
They form salt, water and carbon dioxide
What type of substance reacts with an alcohol to form a carboxylic acid
An oxidising agent
What is the functional of an ester
COO-
What are esters formed from
Reacting an alcohol with a carboxylic acid
What do we call the ester that is formed from ethanol and ethanoic acid
Ethyl ethanoate
What is condensation polymerisation
The process by which monomers combine to form a polymer, while releasing small by-products such as water
What is the general formula for making a polyester
For polyesters, how does condensation polymerisation work
A diol and a dicarboxylic acid bond together As part of the process, the diol and dicarboxylic acid lose hydrogen and oxygen, which bond together to form water
What does biodegradable mean
The substance can be broken down by naturally occurring organisms
What 2 different functional groups are present in all amino acids
Amino group Carboxyl group
How are polypeptides made
Condensation polymerisation between amino acids
What is analytical chemistry
The science of seperating, identifying and quantifying different substances
What is a chemically pure substance
A single element or compound that hasnt been mixed with any other substance
How can impurities affect the melting and boiling points of the sample
Lower the melting point increase the boiling point increase the range over which a substance melts or boils
What physical test can you do to check that a substance is pure
Heat it until it melts or boils. If it melts or boils at a specific temperature then its pure
What is formulation
Mixtures that have been prepared using a specific formula
What are formulations made from
Precise amounts of different components, and each component has a particular function
What is flame emission spectroscopy used for
Identifying metal ions in solution, and measuring their concentration
Outline the process for carrying out flame emission spectroscopy
What are 3 advantages of using instrumental method instead of chemical tests
The instrumental method is very quick The instrumental method is very accurate The instrumental method is very sensitive
What are the 3 disadvantages of using instrumental methods
Expensive Requires specialist training Requires a known comparison to check your reading against
How long ago did the earth form
ABout 4.6 millions years ago
What is the composition of our current atmosphere
78% Nitrogen 21% Oxygen other gases <1
What are the 3 main stages in the evolution of earth’s atmosphere
Volcanoes emitted large amounts of gasEarth cooled, oceans formed, plants and algae evolvedPlants and algae produced oxygen, eventuall forming the atmosphere we have today
How were oceans formed
After 1 billion years, the earth cooled, causing water vapour in the atmosphere to condense into liquid and form oceans
What happened to most of the carbon dioxide in the early atmosphere
It dissolved in oceans The dissolved CO2 then went through a series of reactions to form carbonate precipitates These carbon precipitates formed sediments on the sea bed Some CO2 was also absorbed by green plants and algae so they could photosynthesise
How are coal, crude oil and natural gas formed
Plants or algae absorb CO2 to use in photosynthesis When they die they dont decompose properly Under high temperatures and pressures, the organic material forms coal, crude oil and natural gas
How has the atmosphere changed since the earth was formed
What is global warming
The long term heating of earths atmosphere, observed since the pre-industrial period due to human activities
What is climate change?
Long-term shifts in temperatures and weather patterns due to global warming
Give 4 human activities that have affected the amount of greenhouse gases in the atmosphere
Deforestation Burning fossil fuels Farming of animals As microorganisms break down our waste in landfill sites, releases CO2
Explain what the greenhouse effect is and how it works?
What are some consequences of climate change
Melting ice caps Rising sea levels Reduced biodiversity Changed migration patterns increased extreme weather events
What is a carbon footprint
The total amount of carbon dioxide and other greenhouse gases that are emitted over the full life cycle of a product, service or event
Give 4 factors you would need to take into account when calculating the carbon footprint of a product such as a car
How all the raw materials were sourced The manufacturing process The total amount of fuel and other resources it will use over its lifetime How its disposed of
Give 4 general ways we could reduce the carbon footprint of a product
Creating it using fewer, or more sustainable raw materials Use a more efficient manufacturing process Use renewable energy resources Recycle it rather than disposing of it in landfill
How might governments help reduce carbon footprints
Introduce new laws or regulations Tax companies based on quantity of greenhouse gases they emit Put caps or limits on how many greenhouse gases companies can emit
What pollutants can incomplete combustion produce
Carbon (soot) Carbon monoxide unburnt hydrocarbons
How is soot in the air harmful
If inhaled it can get stuck in our lungs and cause damage, leading to respiratory problems It also cause smog/global dimming
Why is carbon monoxide dangerous
It binds to haemoglobin so less oxygen is transported around the body Lack of oxygen causes fainting, a coma or even death It also has no smell or colour so its hard to detect
How can the combustion of fossil fuels form sulfur dioxide
Some fossil fuels contain sulfur impurities - so when the fossil fuel is combusted, the sulfur becomes oxidised into sulfur dioxide
How can the combustion of fossil fuels form nitrogen oxides
Combustion takes place in engines at high temperatures and pressures These conditions allow nitrogen and oxygen from the air to react together and form nitrogen oxides
How does acid rain form
Nitrogen oxides and sulfur dioxide can dissolve in the water vapour in the atmosphere, forming dilute nitric or sulfuric acid, which falls as acid rain
What are 3 negative effects of acid rain
Kills plants Damages buildings Corrodes statues
What is a ceramic
A grouo if non metal solids with high boiling points that arent made from carbon based compounds
How are clay ceramics made
Dig clay from the ground Mould the clay into the shape that you want Heat the clay at high temperatures in a furnace to harden it into a clay ceramic
How is soda lime glass made
Heat a mixture of limestone, sand and sodium carbonate until it melts When it cools it will form glass
How is borosilicate glass different to sodium lime glass
It is made from a mixture of sand and boron trioxide It has a higher melting pount than soda lime glass
What is a composite material
Composites are made of one material (reinforcer) embedded in another (matrix) This makes the composite much stronger than either of the materials alone
What is the difference between low density poly(ethene) and high density poly(ethene)
What is the difference between thermosoftening and thermosetting polymers
Thermosoftening polymers melt when they are heated and can be remoulded Thermosetting polymers do not melt when they are heated, so cannot be remoulded
How does the structure of thermosoftening polymers relate to their properties
Thermosoftening polymers are made from lots of polymer chains, held together by weak intermolecular forces These forces break easily when heated, causing the polymer to melt It can then be remoulded into a different shape and will harden again when cooled
How does the structure of thermosetting polymers relate to their properties
Thermosetting polymers are made from lots of polymer chains, held together by strong covalent bonds These require lots of energy to break, so dont soften when heated These polymers are hard, strong and rigid
What is corrosion
The process by which metals are slowly broken down by reacting with substances in their environment
What is the word equation for the rusting of iron
Why does iron corrode so much more than aluminium
When aluminium corrodes it forms a protective layer of aluminium oxide, which prevents further corrosion When iron corrodes, the hydrated iron(III) oxide flakes off, then the underlying iron also corrodes
What are the two main methods of preventing rusting
Barrier methods Sacrificial methods
What are 3 ways a barrier method might be applied to prevent rusting
Greasing Painting Electroplating
What does electroplating do
Uses electrolysis to reduce metal ions onto an iron electrode - this process can be used to coat iron with a layer of another metal that wont corrode
