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2 types of changes can occur to materials, the first is a change to the apperance and state of a material, but the material is still made up of the same molecules. This is called a Physical change.
A chemical change occurs between 2 (or more) different substances. The apperance and state of the compound may change, but the important bit is that the chemical formulae of the new product is different to the formulae of the reactants. This is a chemical change
A fire,
describe a fire in 20 words
or give 20 different words that describe a fire,
The FIRE triangle
Only if you have all 3 component of the fire triangle do you have fire. Therefore if you want to stop a fire all you must do is remove one of the smaller triangles and this will cause the fire to stop burning (or prevented from starting)
Methods of Fire Extinguishing
remove the heat
cool down the place of the fire
pouring water on a fire works because it
remove the fuel
Take what is burning out of the location of the fire
Remember to use to the gas emergency switch, this knocks off the gas in the room
remove the Oxygen
Oxygen is needed for fire remove this gas
one common way to remove the oxygen is to blow more dense CO2 in the place of the fire.
In a (clear) Jug, pour some vinegar, spirit vinegar is recommended, to this add some baking powder.
Gentally cover the mouth of the jug with some paper,
over some lit candles 'pour' the gas over the candles, observe
A very good video explaining the ideas of fire, candles .....
judging reactions
the most reactive elements (besides the Alkali metals)
Calcium → Magnesium → Zinc → Copper
Cheetahs Make Zebras Cry,
Cataylsts
Cataylsts are compounds that alter the rate of reaction,
(change the amount of time a reaction takes).
So if you have a slow reaction that is safe you may try to use a cataylst to speed up the reaction, these are known as accelerants If you have a fast reaction that causes a dangerous chemical to be given off then you would use an Inhibitor.
Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. That is the same mass of catalyst remains at the end as was at the start because none of it is used up. The catalyst may participate in multiple chemical transformations.
Catalysts that speed the reaction are called positive catalysts accelerants. Catalysts that slow down the reaction are called negative catalysts or inhibitors.
For demonstration of cataylsts,
- take a sugar cube, try to light it.
- take some ash from burned paper try to burn it
- rub some ash into a corner of the sugar cube and try to light it
- Make some judgements on what you observed
Catalytic converters are used in cars to remove harmful chemicals from their exhausts fumes, a picture of one here
What else do you think might alter the rate of reactions?
Particle Size Temperature
To see light being given off by a reaction
0.4g luminol, 4g sodium hydroxide, 100cm3 bleach, 3 conical flasks,water
mix the bleach and 900cm3 of water, stopper it
in other 1litre of water (1dm3) add the luminol and NaOH
Check temperatures
check contents apperance
lower the lights and pour the 2 solutions at the same rate into the 3rd conical flask.
observe.
Check temperatures
Endothermic reaction
A reaction that takes in heat
For extra WOW place on a plank of natural wood, pour water over the wood do experiment on the wet wood
Citric acid, Baking soda Sodium Hydrogen Carbonate, Glass beacker
make up a saturated solution of citric acid, measure the temperature
Add the baking powder stirring constantly with the thermometer
further
write the reaction
A Solid Solid reaction
Solid lead nitrate and solid potassium iodide are shaken together in a small jar. They quickly react to make yellow lead iodide
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