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PoppyG
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What are reactions that release energy called?
- exothermic -gives out energy in form of heat
- combustion / burning examples of exothermic
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What are reactions that take in energy called?
- endothermic
- less common
- usually causes temperature to drop
- e.g. thermal decomposition where heat needs to be applied
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acid added to alkali - what sort of reaction?
exothermic
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Give an example of endothermic reaction?
dissolving ammonium nitrate in water - causes a drop in the temperature of the water
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what effect do any changes in bonds have on what type of reaction is taking place?
- in a chemical reaction old bonds are broken, new ones are formed.
- energy must be supplied to break bonds (endothermic process)
- energy is released when new bonds are formed (exothermic process)
- If more energy released the reaction is exothermic.
- If more energy is required the process is endothermic
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How are ice packs for injuries made?
- cold pack has an outer bag of ammonium nitrate and an inner bag of water.
- Pressure causes inner bag to break allowing them to mix, ammonium nitrate dissolves in the water
- this is an endothermic reaction
- it draws heat from the injury
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What is specific heat capacity?
amount of energy required to raise the temperature of a 1 gram of a material by 1 degree C.
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What is the specific heat capacity of water?
4.2 J / g / °
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What is the calorimetric experiment?
- heat water by burning a liquid fuel
- measure how much fuel burnt and temperature change of the water
- shield water from draughts
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What are the calculations used in the calorimetric experiment
- find mass of fuel used by taking away the final mass of the burner and fuel from the initial mass of fuel and burner
- energy used (in Joules) = (mass of water ) x (specific heat capacity of water
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formula for calorimetric energy?
- energy transferred = mass of water (grams) x specific heat capacity of water (4.2 J/g °C) x temp change (°C)
- energy = m x c x temp change ( symbol is triangle then "T" in book)
- for energy per gram of fuel divide by mass of fuel burnt
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How can you make sure energy of fuels test results are fair?
- Repeat experiment several times
- keep everything except fuel the same
- ignore any anomalous (Exceptional) results
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What is the rate of a chemical reaction?
- how fast reactants are changed into products
- reaction is over when one reactant is completely used up
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Examples of slow chemical reactions?
- rusting of iron
- chemical weathering like acid rain damage to limestone buildings
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Example of moderate chemical reaction?
a metal, e.g. magnesium, reacting with dilute acid to produce a steady stream of bubbles
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Example of a fast chemical reaction?
- burning
- explosion is really fast - over in fraction of a second
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How can you do an experiment to follow a reaction?
- rate of reaction that a gas is produced;
- measure how quickly gas is produced
- measure mass falling a gas released, or
- measure volume of gas given off
- plot results against time
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What is the collision theory?
- rate of reaction depends on;
- collision frequency of reacting particles (how often they collide)
- more collisions the faster the reaction
- energy is transferred during collision
- particles must collide with enough energy for the collision to be successful.
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what does the amount of product you get from a reaction depend on? (the yield)
- depends on the amount of reactant you start with
- more reactant = more particles = more reactions = more product
- amount of product is directly proportional to the limiting reactant (half particles of limiting reactant you get half the yield)
- limiting reactant is the reactant that is all used up.
- any of other reactant left is in excess
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Collision theory - name four factors that increase rate of reaction?
- 1 increasing the temperature
- 2 increasing concentration or pressure
- 3 smaller solid particles / more surface area
- 4 a catalysts
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What is the effect of temperature on reactions?
- temp increased = particles move more quickly
- quicker particles = more collisions
- temp increased = more energy in collisions
- reactions only if collisions with sufficient energy.
- Therefore increase of temp - increases rate of reaction.
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What effect does concentration or pressure on rate of reaction
- if solution more concentrated more particles of reactant in same volume
- collisions more likely
- in gas, increase pressure means molecules are more crowded so frequency of collision increases
- both increase rate of reaction
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effect of smaller solid particles / more surface area on rate of reaction?
- if reactant solid, breaking it up into smaller bits increases surface area
- particles around it have more area to work with
- frequency of collisions increases
- examples;
- soluble pain killer dissolve quicker if broken up
- fine combustible powders in air burn very very fast - with spark can explode, factories making custard powder and flour and powdered sulfur have to be very careful
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effect of catalyst on rate of reaction?
- catalyst = substance which speeds up reaction without being chemically changed or used up
- only need tiny bit to catalyse large reactions
- catalysts fussy as which reactions they work for
- works by giving reacting particles a surface to stick where they bump into each other
- reduces energy required
- increases successful number of collisions not the overall number of collisions
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In periodic table, elements have two numbers
what is the bigger one, at the top?
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In periodic table, elements have two numbers
what is smaller number at the bottom?
atomic mass (also known as proton number)
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What is relative formula mass?
- all relative atomic masses added together
- Mr
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How do brackets effect the relative formula mass of compounds?
- If there is a 2 after brackets, e.g Ca(OH)2 , then there is two times everything within the brackets.
- e.g. Ca =40, O=16, H=1.
- therefore =40 + (16 +1) x 2
- therefore = 40 + 34 = 74
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What happens to atoms in a chemical reaction?
- No atoms are destroyed
- No atoms are created
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What happens to mass in chemical reactions?
- as no atoms created or destroyed there are same number and type of atoms on each side of a reaction equation
- mass is conserved
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What is atom economy of a reaction?
- how much of the mass of the reactants is wasted when manufacturing a chemical.
- atom economy = atom Mr of desired product / total Mr of all products x 100
- 100 atom economy means all atoms in reactants turned into useful desired products.
- higher % greener
- useful by-products increase to increase
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How is percentage yield worked out?
actual yield / predicted yield x 100
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Give 4 reasons why yields are less than 100% for chemical reactions?
- 1 evaporation
- 2 not all reactant react to make product, e.g. Haber process - reversible reaction so reverse reaction taking place
- 3 filtration - will always lose some solid or liquid
- 4 transferring liquids - some always left behind
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What are the benefits of batch production and when is it used?
- pharmaceutical drugs - complicated to make with fairly low demand.
- batch production cost effective as low start up cost - cheaper multi purpose machine
- flexible
- (however labour intensive - set up, cleaning etc, plus hard to keep same quality)
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When is continuous production used and what are the pro's and con's?
- large scale industrial manufacture of popular chemicals E.g Haber process for ammonia
- production never stops therefore not emptying reactor etc
- runs automatically
- quality is very consistent
- start up costs huge and needs to be run at full capacity.
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Why are pharmaceutical drugs expensive?
- research and development
- trialling to get legal approval
- manufacture - multi step, labour intensive
- takes about 12 years & £900m to develop new drug and get on market
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How do you extract a substance from a plant?
- 1) crush
- 2) boil and dissolved in suitable solvent
- 3) extract with chromatography
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What happens to a pure substances during chromatography?
- pure substances are not separated during chromatography.
- It will move in one blog
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What is the effect on boiling and melting points if a substance is not pure?
- Each pure substance will have specific melting and boiling points.
- If the substance is not pure these will change.
- e.g. water 0°C, 100°C - if add salt may melt at -2°C.
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What are allotropes?
- different structural forms..
- .. of same element..
- .. of same physical state...
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Name two allotropes of carbon
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Four facts about diamond?
- 1) diamonds are lustrous (sparkly) and colourless (ideal for jewellery)
- 2) each carbon atom form 4 covalent bonds. in a very rigid covalent structure. (ideal cutting tools).
- 3) all those strong covalent bonds take a lot of energy to break -
very high melting point.4) doesn't conduct electricity because it has no free electrons or ions.
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Five facts about graphite?
- 1) graphite is black and opaque but still kind of shiny.
- 2) each carbon atom only forms three covalent bonds creating sheets of carbon atoms which are free to slide over each other.
- 3)layers are held weakly so they are slippery and can be rubbed off onto paper (pencil) (also ideal lubricating material).
- 4) graphite has high melting point - the covalent bonds need loads of energy to break.
- 5) since only three of each carbon's four outer electrons are used in bonds - there are lots of delocalised (spare) electrons that can move. This means graphite conducts electricity.
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Diamond and graphite are G.... M........ S.........?
Giant Molecule Structures
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Why can carbon form structures like diamond and graphite?
- Carbon can form lots of covalent bonds with itself.
- This means can form giant molecular structures.
- Due to all covalent bonds, giant molecular structures are strong, high melting points, don't dissolve in water.
- Don't usually conduct electricity - as no free electrons or ions (note graphite is an exception).
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What are fullerenes?
- molecules of carbon
- shaped like closed tubes, or hollow balls or ellipsoid
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How can fullerenes be used?
- can be used to 'cage' other molecules
- another atom or molecule can be inside
- this can be used to deliver a drug into the body e.g. slow release
- fullerenes can be joined to form nanotubes - tiny hollow carbon tubes
- nanotubes have huge surface area
- nanotubes could help make great industrial catalysts
- individual catalysts could be attached to the nanotubes
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