Patterns & Reactivity Key Notes

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Patterns & Reactivity Key Notes
Properties of Metals
Property
Metals
Non-metals
State at room temperature
Usually solid
½ gas ½ solid
Conduction of heat and
electricity
Good conductors
Bad conductors
Flexibility (can shape it)
Can be shaped
Cannot be shaped
Malleability (can bend it)
Malleable (can be bent)
Brittle (break when bent)
Sound when hit
Ringing noise
Dull noise
Are they magnetic?
Some are
Not magnetic
Oxides are acids / bases
Bases
Acids
Reactivity series
Some metals are more reactive than others (remember gold in water is
fine, sodium in water is not)! We can order the reactivity of the metals,
from most reactive to least
This is the reactivity series!
Most reactive
Least reactive
Potassium
Sodium
Calcium
Magnesium
Aluminium
Zinc
Iron
Lead
(Hydrogen)
Copper
Silver
Gold
Platinum
Some metals are more reactive than others. A displacement reaction is
where one metal kicks another out
A more reactive element reacts with a compound and pushes out a less
reactive “rival” element
Metal Reactions
metal + water  metal hydroxide + hydrogen
metal + oxygen  metal oxide
metal + acid  salt + hydrogen
metal oxide + acid → salt + water
metal carbonate + acid → salt + water + carbon dioxide
Test for carbon dioxide is limewater (goes cloudy)
Acid + Alkali
A chemical reaction occurs if you mix an acid and an alkali. The reaction is
called neutralisation. A neutral solution is made (if you add the right
amount of acid and alkali)
acid + alkali → salt + water
Acids are sour / bitter. Weak dilute acids can be irritants (will cause your
skin to become red and blister). Stronger, concentrated acids can become
corrosive (attack metals and destroy skin).
Alkalis are sometimes referred to as bases (alkalis are soluble bases).
Alkalis are the opposite pH of acids. You will have used alkalis at school
(sodium hydroxide), and these are just as dangerous as acids. Alkalis feel
soapy when they touch your skin. Weak alkalis are in toothpaste; baking
powder; stomach tablets; and used for a variety of cleaning agents (as
they react with oil and fat)
Salts are extremely useful chemicals. There are many different salts
which can be produced, and their uses are vary varied. They are produced
when a neutralisation reaction occurs: 




The salt can be worked out from looking at the reactants we
started with
Hydrochloric acid makes a metal chloride
Sulphuric acid makes a metal sulphate
Nitric acid makes a metal nitrate
Phosphoric acid makes a metal phosphate
Exothermic Reactions
Most chemical reactions involve energy change. Often this energy is in
the form of heat
Exothermic reaction - energy is given out (temperature increases)
Endothermic reaction - energy is taken in (temperature decreases)
Exothermic - e.g. combustion of fuel (heat given out by the chemicals to
the surroundings)
Endothermic - e.g. ice cube melting in your hand (heat taken away from
the surroundings to the chemicals (which is why your hand feels cold
when you hold an ice cube and it melts))
Combustion is the chemical reaction, which takes place when a substance
burns. The substance reacts with oxygen, releasing energy (heat and
light). Combustion is extremely important (>90% of the world’s energy
comes from combustion reactions (e.g. fossil fuels such as coal, natural
gas and petrol)
Combustion needs:  Heat
 Fuel
 Oxygen
A good supply of oxygen is needed for a fuel to burn completely and
release as much energy as possible. If there is a plentiful supply of
oxygen we get complete combustion
However, if there is not enough oxygen then the fuel will not burn
completely, wasting both the fuel and reducing the energy released. If
there is not enough oxygen we get incomplete combustion
Chemical Reactions
Many changes can occur when a chemical reaction takes place. These can
include: 




New compounds form – with new properties
There may be a colour change
Heat may be released
A gas may be given off
The pH may have changed (compound formed is acidic / alkaline)
In all chemical reactions, the mass of the reactants is the same as the
mass of the products. No atoms are gained or lost - they are just
rearranged in different ways
mass reactants  mass products
100g of reactants  100g of products
Balancing Equations
Each element has its own symbol(s) - all found in the periodic table
Every symbol begins with a capital, and may have one or more other noncapital letters which follow
A chemical reaction can be described by the process: reactants → products
There must always be the same number of atoms on both sides. Numbers
can only be put in front of the formula when it is needed.
E.g.
2H2 + O2 → 2H2O
3H2 + N2 → 2NH3
C3H8 + 5O2 → 3CO2 + 4H2O
2Al + 3CuO → Al2O3 + 3Cu
K2O + H2O → 2KOH
CaCl2 + 2AgNO3 → 2AgCl + Ca(NO3)2
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