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chemistry 1 (COMBUSTION AND AIR POLLUTION (combustion reactions are an…
chemistry 1
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ENDOTHERMIC + EXOTHERMIC
EXOTHERMIC REACTION =
one which gives out energy to the surroundings . this is usually shown by RISE IN TEMPERATURE of surroundings
ENDOTHERMIC REACTION =
one which takes in energy from surroundings .this is usually shown by a fall in temperature of the surroundings .
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activation energy
is the minimum amount of energy required to start a reaction (break bonds)
it is difference between reactants and highest point of curve.
if energy input is less than activation energy won't be enough to start a reaction ( nothing will happen)
greater activation energy = bigger difference between reactants and top of curve
greater energy change = bigger difference between reactants and products
POTABLE WATER
WATER SOURCES:
ground water - from aquifers (rocks under ground that trap water)
waste water - from water thats been contaminated by humans
salt water - from the sea
TREATMENT TO MAKE POTABLE
GROUND WATER = usually aeration- water is mixed with air to increase levels of dissolved oxygen
this forces the other dissolved gases out the waterand removes ions.
water is then filtered
WASTE WATER
has to be filtered
air is pumped through aerobic bacteria to grow and break down
FOR WASTE WATER THAT IS CONTAMINATED
involve adding chemicals (uv radiation /using membrane)
uses less energy than ground water treatment but requires more processes
DISTILLING SEA WATER:
in dry countries needed to get clean water.
on small scale use solar still - water covered in clear dome and left in sunlight to evaporate and then the water on lid condenses can be collected leaving behind salt.
on larger scale traditional distillation apparatus are used which involves burning fossil fuels.
reverse osmosis can be used using membrane that allows water molecules to pass through but stops salt and other large molecules.
have less processes but use lots of energy- making expensive and impratical
CHLORINATION:
chlorine gas is bubbled though to kill bacteria and other microbes..
some times it can eat with certain compounds to make dangerous chemicals levels of these chemicals have to be closely monitored. benefits out weigh the risks.
STATES OF MATTER
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chemical change = bonds between atoms(reactants) break and atoms change place rearranging into a new chemical
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BOND ENERGIES
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during chemical reaction exisiting bonds are broken and new bonds are formed
bonds breaking is an ENDOTHERMIC process--------->positive energy change
a bond formation is an EXOTHERMIC process --------->negative energy change
every chemical bond has a particular bond energy associated with it
you can use these known bond energies to calculate overall energy change for a reaction
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CHEMICAL FORMULAS
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ionic compound
formula for ionic compound tells you ratio
e.g sodium chloride , NaCl , has one chlorine for every one sodium atom.
CHEMICAL EQUATIONS
Chemical changes are shown using chemical equations
e.g : methane burns in oxygen given carbon dioxide and water
METHANE + OXYGEN--> CARBON DIOXIDE + WATER
Left side = reactants (they react)
right side = products (they have been produced )
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symbol equations must be balanced
always same number of atoms of each element on both sides they can't just disappear (this is called conservation mass)
balance equation by putting a number in front of formulas when needed (ue method divide down the equation and see how many on each side) 
CHANGING STATES
SOLID
solid - liquid = melting
liquid - solid = freezing LIQUID
liquid - gas = boiling
gas - liquid = condensing GAS
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