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C2 (2) (Rates of Reaction (How much chemical reacts, or is formed, in a…
C2 (2)
Rates of Reaction
How much chemical reacts, or is formed, in a given time
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You can alter the rate of chemical reaction by doing one or more of these: increasing temperature, increasing the concentration of a reactant, using smaller pieces of a reactant, or adding a catalyst
Polymer Chains
Polymers Vary
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HDPE and LDPE are made from the same monomer but at different temperatures, pressures and a different catalyst
Thermosoftening polymers is a tangle of smooth chains(slide past each other = melt) while thermosetting polymers as more side chains and more links to other chains(cannot slide = cannot melt)
Intermolecular forces
Polymer molecules are long covalent chains made from carbon atoms, with various side groups attached
Intermolecular forces between molecules are weak because the molecules are so large the effect is greater, giving them higher melting points than expected
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Metallic Properties
Alloys
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Pure Metal = atoms all the same size(regular layers which slide easily). Alloys = different size alloys that disrupt regular lattice (can't slide making alloys harder and less malleable)
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Shape memory such as nitional are useful as when warmed they return to their original shape(used for dental braces and plates to hold broken bones together)
In metals, the outer electrons of each atom are delocalised or free to move
As the sea of electrons can move, the metal is able to conduct electricity
The structure allows metals to bend, as the positive ions can move around each other
Conduction
When a potential difference is applied to a metal, the delocalised electrons flow from the negative connection towards the positive connection creating an electrical current
Heating a metal makes the particles in it vibrate more, The vibrations pass along the metal lattice, 'warming' the metal so metals are good conductors of heat
Modern Materials
Applications
Modern materials include 'Smart' materials(photochromic, thermochromic and shape memory alloys). Very small materials are nanoparticles
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Carbon has a several nanoparticles, such as nanotubes, and Buckminsterfullerene(C60)
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Fullerenes
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Possible to trap a molecule inside the sphere, so allowing highly toxic drugs to be carried to specific sites in the body to kill infections or cancerous cells
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Making Chemicals
Routes and Conditions
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Condition for reactions
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Pressure(higher compresses gas molecules, giving more molecules in the same volume and leading to faster reaction)
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Chemical Calculations
Chemists calculate the correct masses of reactants to use to make products, so that only the smallest amounts needed are used to make the products and waste products are kept to the minimum
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Chemical Composition
Empirical Formulae
The relative quantities of each element present in a compound can be worked out using the percentage composition needed
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How Much Product
Percentage Yield
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Reactants are rarely 100% pure. The mass of actual reactant is less than the mass weighed out, so forms less product: the same reactants can form different products: if the reaction is reversible, some of the products turn back into reactants
To compare the effectiveness of making a chemical in different ways, we calculate the percentage yield
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Percentage Yield, Economics and the Environment
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Maximising percentage yield makes economic sense. Less raw materials are needed and less are wasted in making unwanted by-products that have to be disposed of
Collision Theory
Explaining
For a chemical to occur, the reactants must collide with each other.
The more collisions, the faster the rate of reaction (not all collisions cause reactions)
The collisions need to be hard enough to cause the reactants to react(can be done by higher temperature, increasing the concentration, increasing the pressure, suing smaller particles of a solid, adding a catalyst)
How Much Change?
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Cutting a cube of solid reactant into eight, doubles its surface area and doubles the rate
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Adding Energy
The steeper the graph's curve, the faster the rate
Activation Energy
To cause a reation, particles must collide with sufficient energy to break bonds
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Quantities
We can work out the relative reaction masses of each reactant or product by multiplying the Ar or Mr by the number of reacting molecules of each gas
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