Chem 2

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Note on Chem 2, created by emily.wright03 on 05/29/2013.

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  Enthalpy; the heat energy content of a system  measures in kilojoules  The enthalpy change is calculated by subtracting the total enthalpy of reactants from the total enthalpy of the products Exothermic reactions; release heat energy therefore the enthalpy change is always negative Endothermic reactions; absorb heat energy therefore the enthalpy change is always positive Standard  conditions = 298K 100 kPa which are used to calculate standard enthalpy changes  Standard enthalpy of formation - the enthalpy change when one mole of a compound is formed from its elements in their standard states  Standard enthalpy of combustion- the enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions  q= mc (delta)T Heat = mass of substance x specific heat capacity x temperature change  to calculate an enthalpy change using q= mc (delta)  use mass of liquid, x specific heat capacity x temperature change  then calculate the moles of solid dissolved  one mole of solid would absorb (1) / (2) which is either +ve (endothermic) or -ve (exothermic)   a cooling curve shows the initial temperature line and the finial temperature line which is then extrapolated to determine the the temperature change at point of mixing Hess' Law- if a reaction can occur by more than one route the overall enthalpy change is independent of the route taken  energy cannot be created or destroyed only changed from one form to another  to calculate the standard enthalpy for a reaction you can use the standardard enthalpy of formation (both arrows up) (sum of formation of products) - (sum of formation of reactants) using enthalpy of combustion the arrows go down  Bond enthalpy - the standard enthalpy change associated with breaking one mole of bonds in a gaseous substance into gaseous atoms  Mean bond enthalpy- the energy needed to break or dissociate a bond averaged over different molecules  The enthalpy values change slightly depending upon what environment is in  the overall enthalpy change for a reaction is the difference between the energy needed for the bond breaking and the bonds forming 

the rate of a chemical reaction is measured as the amount of product made or reactant used up in a certain time  rate of reaction = increase in concentration                                         time  for a reaction to occur the correct particles must collide, at the right angle with the correct energy the temperature, concentration, surface area and presence of a catalyst all affect the rater of reaction  activation energy- the minimum amount of energy with which particles must collide in order for a reaction to occur  increasing the temperature causes the rate of reaction to increase  a Maxwell-Boltzmann distribution of molecular energies diagram shows that only a very small fraction of the molecules have a very high or very low energies, the curve is not symmetrical, the curve does not touch the x axis on the right hand side. as the temperature increases the energy distribution moves to the right - for a small increase in temperature there is a slight shift, for a larger temperature increase the graph alters more dramatically  a change in temperature does not cause any change to the activation energy it just increases the number of particles present to posses the activation energy  Catalyst- alters the rate of reaction but remains unchanged at the end of the reaction by providing an alternative route with a lower activation energy Catalysts have no affect on the Mazwell-Booltzmann curve they just move the activation energy  Heterogeneous catalysts are in the a different phase from the reactants  Homogeneous catalyst are in the same phase as the reactants  increasing the concentration of reactants will (most of the time) increase the rate of reaction as there is an increased probability of the particles colliding  

ENTHALPY the heat energy content of a system 

EXOTHERMICreactions that release heat energy which therefore have a negative enthalpy change

ENDOTHERMICreactions that absorb heat energy which results in a positive enthalpy change 

STANDARD ENTHALPY OF FORMATIONthe enthalpy change when one mole of a compound is formed from its elements in their standard states 

STANDARD ENTHALPY OF COMBUSTION the enthalpy change when one mole of a substance is completely burned in oxygen under standard conditions  

HESS'S LAWif a reaction can occur by more than one route the overall enthalpy change is independent of the route taken

BOND ENTHALPYthe standard enthalpy change associated with breaking one mole of bonds in a gaseous substance into individual gaseous atoms

MEAN BOND ENTHALPY the enthalpy needed to break or dissociate a bond averaged over different molecules

RATE OF REACTIONthe amount of product made or reactant used up in a certain time 

ACTIVATION ENERGYthe minimum energy which particles must collide for a reaction to occur

HETEROGENEOUS CATALYSTa catalyst in a different phase from the reactants 

HOMOGENEOUS CATALYSTa catalyst in the same phase as the reactants

LE CHATILIERS PRINCIPLEwhen the conditions of an equilibrium are changed then the position of the equilibrium will shift to minimize the change

DYNAMIC EQUILIBRIUM at equilibrium the reactants are still making the products and the  products are still reacting to make reactants 

OXIDATION is the LOSS of electrons 

REDUCTION the GAIN of electrons

roasting can be used to convert metal sulfides to metal oxides roasting reactions are strongly exothermic  sulfuric acid is manufactured using the contact process - in which sulfur dioxide is oxidised in the presence of a vandium oxide catalyst.  sulfur trioxide is produced and is then absorbed into concentrated sulfuric acid which forms an oily liquid which then is diluted again to form a larger volume of sulfuric acid the most reactive metals are extracted using electrolysis - Al, K, Na, Ca and Mg - but electricity is expensive so metals produced this way are likely to be expensive  some metals can be extracted by using a more reactive metal for example Titanium is from Titanium chloride being reacted with Magnesium or Sodium  other metals can be extracted by the use of Hydrogen which can be manufactured by; cracking of crude oil, reaction of methane with steam or the reaction of carbon with steam  carbon can also be used to extract less reactive metals - it is cheap and can be used in the extraction of iron, manganese and copper IRON EXTRACTION - using a blast furnace1. Coke burns in air, this raises the temperature2. Calcium carbonate decomposes in the heat3. Coke reduces carbon dioxide to form Carbon Monoxide4. Carbon Monoxide resuces the iron oxide at around 1500 c5. Impurities in the iron react with calcium oxide from the decomposed limestone forming liquid Slag Manganese can be reduced by carbon monoxide to form MnO which can then be reduced again using carbon  Copper Oxide can be heated strongly with carbon  BUT can be extracted from Chalcopyrite in a single stage by using Oxygen ALUMINIUM forms strong alloys, is a good conductor of electricity, has a low density, resists corrosion  electrolysis only works when a substance is molten or dissolved - aluminium oxide has a melting point of 2050 C - to reach these temperatures would be incredibly uneconomical Aluminum oxide is dissolved in molten cryolite which causes a much lower melting point (950 C) and allows electrolysis  Aluminium ions are attracted to the Cathode ( Al 3+   ---> 3e-  + Al  ) Oxide ions are attracted to the Anode ( 2O 2-   ---> O2  + 4e- )

TITANIUM - the Hunter process 

chapter 5,6,7

chapter 11,12,13

definitions

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