Chemistry Module 3

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How can you decide if a reaction is endothermic or exothermic?
Measure the temperature before and after the experiment - If there is an increase, then it is exothermic, if there is a decrease then it is endothermic
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What makes a reaction exo/endothermic?
Bonds being broken require energy and bonds made release energy. If the energy released in bond making is greater than the energy supplied in bond braking, then it is exothermic
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What is calorimetric experiment?
It is an experiment which involves heating water by burning a liquid fuel. If you measure how much fuel you've burned and the temperature change of water, you can work out how much energy is supplied in each gram of fuel
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How do you complete a calorimetric experiment?
Put fuel in a spirit burner and weigh the burner full of fuel. Measure some water into the coper calorimeter. Take the initial temperature and light the spirit burner. When the temperature has increased by 20-30*C blow out the flame. Reweigh the fuel
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What is the equation for energy transferred?
Energy Transferred = Mass of Water x Specific Heat Capacity of Water x Temperature Change
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What is the equation for energy given out per gram?
Energy Given Out Per Gram (J/g) = Energy Released (J) / Mass of Fuel Burned (g)
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Why do you have to use a draught excluder in a calorimetric experiment?
To make sure as much heat as possible goes into heating up the water.
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How do you keep a test fair?
To compare results, the test must be the same each time - Everything except the fuel used must stay the same / In order for results to be reliable, the test must be repeated and any anomalies excluded
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What does rate of reaction depend on?
The collision frequency of reacting particles - the more collisions there are, the faster the reaction / The energy transferred during a collision - particles have to collide with enough energy to react
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Why might a reaction stop?
If the limiting reactant is used. The reaction cannot go as there is nothing to react with - any other reactant leftover is called excess
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How does increasing the temperature increase the rate of reaction?
This means the particles have more energy and are traveling faster. This means there are more possible collisions and the increase in energy means it is more likely there will be successful collisions
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How does increasing the concentration/pressure increase the rate of reaction?
This means there are more reactant particles in an area and so more collisions occur / Increase in pressure means a smaller space and so it is more likely for particles to collide when there is less space
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How does increasing the surface area of the reactant increase the rate of reaction?
More surface area available means more particles available to the reactant and so the frequency of collisions increase
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How does a catalyst increase the rate of reaction?
This means particles have a surface to stick to where they can collide - reduces the amount of energy needed to react. Overall number of collisions isn't increased but the number of successful collisions is
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What is Atom Economy?
The percentage of reactants that are changed into useful products and so lets you see how much reactant is wasted
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What is the equation for Atom Economy?
Atom Economy = ( Total Mr of Desired Products / Total Mr of All Products ) x 100
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Why is it better to have a high atom economy?
Resources are used up slower / less waste to dispose of / more profitable - less raw materials to buy, less waste to move etc.
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What is the equation for percentage yield?
Percentage Yield = ( Actual Yield (g) / Predicted Yield (g) ) x 100
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What prevents having a 100% yield?
Evaporation - liquids evaporate all the time / Not all reactants react to make product - some reactions are reversible / Filtration - When filtering happens, products are always left behind / Transferring Liquids - Liquid is lost when transferring
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What are the advantages of batch production?
It's flexible - several different products can use the same equipment / Start-up costs are relatively low -
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What are the disadvantages of batch production?
It's labour intensive - equipment has to be set up and cleaned manually / Difficult to keep the same quality from batch to batch
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What are the advantages of continuous production?
Production never stops / It runs automatically / The quality of product is consistent
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What are the disadvantages of continuous production?
Start-up costs are huge / It isn't cost effective to run at less than full capacity
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Why do pharmaceutical drugs cost a lot?
Research and Development - involves paying a lot of highly trained scientists / Trialing - time consuming to go though tests to prove it is legally safe / Manufacture - cost of labour, materials and energy
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How can you test the purity of a substance?
Chromatography - the substance shouldn't seperate out / Boiling and Melting Points - pure substances should have specific boiling and melting points, impurities will cause melting points to be too low and boiling points too high
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What is an allotrope?
Allotropes are different structural forms of the same element in the same physical state
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Why are diamonds used in jewellery and cutting tools?
(J) They are lustrous and colourless / (C) Every carbon atom has 4 strong covalent bonds in a very large structure making it very hard - these bonds mean it has a high melting point - No free electrons means it doesn't conduct electricity
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What are the properties of graphite?
It is black, opaque and slightly shiny / Each carbon atom only has 3 bonds creating sheets of carbon atoms which are free to slide over each other. The bonds that hold the layers together are weak, can be rubbed off - ideal for pencils and lubricants
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How do graphite and diamond differ/compliment each other?
They both have high melting points as covalent bonds require a lot of energy to break / Graphite can conduct electricity as it has only made 3 bonds and has lots of delocalised electrons which can move
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What is special about diamond and graphite's structure?
Carbon can form bonds with itself and so make giant molecular structures. Because of all theses bonds, these structures are strong, don't dissolve in water and have HBP. Giant structures generally don't conduct electricity
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What are Fullerenes?
These are molecules of carbon shaped like a tube or enclosed ball. They are a type of nanoparticle and can be used to cage other molecules
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What uses are there for fullerenes?
They can act as cages and so could be a new way of delivering a drug / They join together to form nanotubes - with such a large surface area, they could be industrial catalysts - the individual catalyst molecules could be attached to the tube.
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Other cards in this set

Card 2

Front

What makes a reaction exo/endothermic?

Back

Bonds being broken require energy and bonds made release energy. If the energy released in bond making is greater than the energy supplied in bond braking, then it is exothermic

Card 3

Front

What is calorimetric experiment?

Back

Preview of the front of card 3

Card 4

Front

How do you complete a calorimetric experiment?

Back

Preview of the front of card 4

Card 5

Front

What is the equation for energy transferred?

Back

Preview of the front of card 5
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