chemical reactions:

Activation energy:
= minimum amount of energy required for a reaction to occur
(must reach/overcome activation energy)


  • catalysts create alternate pathways witch lower activation energy
  • heat energy can increase the temperature witch increases the likelihood of overcoming activation energy

(particles must collide with enough energy, regularly, at correct orientation to have a successful collision)

Precipitation reactions:

what is a precipitate:
A precipitate is an insoluble solid that forms when certain ions are combined


s = solid / precipitate (insoluble)
aq = aqueous/ no precipitate (soluble)


precipitate = PPT

2 solutions mix & a solid is possibly formed


A solid precipitate may form when 2 soluble (aq) solutions are mixed and the ions are exchanged, to form new ions that may now be insoluble (s), this is the precipitate


AB (aq) + CD (aq) = AC (aq) + BD (s) (switching partners)

you may observe the mixture becoming cloudy when the solutions are mixed, rather than transparent (like it was at the start)
this will happen if a PPT is formed

full formula = word + balanced symbol equations


ionic formula = only the ions included in making the PPT


spectator formula = ions that are involved but don't make the PPT

precipitation
reactions to learn:

all precipitates are white, except...


lead ioide = yellow
copper hydroxide = blue
iron(II) hydroxide = light green
iron(II) carbonate = light gree
copper carbonate = blueish green / turquise

all solutions colouless, excpet...


copper sulfate = blue
copper nitrate = blue
copper chloride = greeny-blue
iron(II) sulfate = pale green

Reactions of metals:


when metals react, the atoms witch make up that metals, loose electrons & metal ions are formed.
the electrons that are lost - go to the substance that the metal is reacting with.


  • all metals do different things
  • reactios of metals are always exothermic

  • If the element doesn't really 'want' to loose electrons, then its quite unreactive (& visa versa)


  • metals reactivity depends on its ability to loose & gain electrons. the easier it looses /gains electrons the more reactive it will be


    (generally the least electrons it must loose, the easier- but not always)


  • very reactive metals will react with both water and acid, however


    less reactive metals will only react with acid

Activity series:
The activity series of metals lists metals in order of reactivity

Our Activity series:


high
Ca
Mg
Al
Zn
Fe
Pb
(H)
Cu
Ag
low


high = more reactive metal = atoms loose
valence electrons more easily = easily form ions


low = less reactive metal = atoms loose valence electrons less easily = doesn't from ions easily


(acids are more reactive than water, so all these metals will react more strongly in acid)

(H) = Hydrogen


- metals above 'H' will react with acids, water & oxygen

  • metals below 'H' in the series are likely to only react with acid, if anything

equations with metal and acid:


metal + acid = metal compound + H2
metal + water = metal hydroxide + H2


(H2 = hydroxide)


examples:


calcium + water = calcium hydroxide + hydrogen
Ca = Ca2+ + 2e-
2e- + 2H2O = 2OH + H2(g)


Ca + 2H2O = Ca(OH)2 + H2(g)


magnesium + hydrochloric acid = magnesium chloride + hydrogen
Mg = Mg2+ + 2e-
2e- + 2HCL = 2Cl- + H2(g)


Mg + 2HCL = MgCl2 + H2(g)



to test for Hydrogen gas:


the pop test
a lit splint is hovered over the top of the test tube, if it makes a pop sound, then the gas is hydrogen gas (the pop is the hydrogen exploding)

Displacement reactions:


A reaction metal where;
you start with one metal
& finish with another
metal/substance

Decomposition reactions:

Combination reactions (synthesis reactions):


2 or more substances chemically bonded together = produce a single compound

  • the more reactive element displaces the less reactive element from its compound


    (you can use the activity series to work out


    witch element is more reactive)


  • if the more reactive metal was already a cation before the reaction occurred, then it will just remain a cation & no displacement reaction has occurred

After the reaction has occurred:


  • the most reactive metal = forms / remains a cation


    (and is observed as a compound with the spectator ion)


  • the metal solid that is formed/remained = the least reactive metal




- most reactive metal forms / remains an ion / cation (aq)
- least reactive metal forms / remains an atom (s)

example:

A piece of copper -Cu metal is added to a
solution of zinc nitrate -Zn(NO3)2


Copper metal contains = Cu atoms
zinc nitrate solution contains = Zn2+ ions (Zn(NO3)2)


  • zinc is a more reactive metal than copper (higher in activity series)
  • therefore, zinc atoms will tend to loose electrons instead of copper atoms

Zn(s) = Zn2+ + 2e-
2e- + Cu2+ = Cu(s)
Cu(NO3)2 (aq) + Zn (s) = Cu (s) + Zn2+ (aq)


without spectators: Cu2+ (aq) + Zn (s) = Cu(s) + Zn2+ (aq)


observations: (how to write about them)


example with Cu(NO3)2 (aq) + Zn (s)


Copper Nitrate is a blue solution, when the grey solid zinc is added to the solution and a displacement reaction occurs. the zinc metal corrodes to form the solution Zinc nitrate and the solution turns from blue to colorless. the Cu2+ ion displaces from the Cu(NO3)2 solution to form Cu metal around the outside of the remaining zinc, the Cu is a brownish red solid.


The Zn is more reactive than the Cu witch is why it looses electrons more easily and therefor is more likely to form the ion. you know this is a displacement reaction because you start with one metal and finish with another.


electrons transfer:
Zn atoms loose electrons to make Zn2+ ions and Cu2+ ions gain those electrons to form Cu atoms.

simple chemical substances are joined together to make 1 more complicated chemical substance


  • the reactions can occur between 2 elements, or compounds

(many combination reactions require the reactants to be heated, in order to make the reaction occur)


- combination reactions are exothermic

2 types of reactions:

Ionic Reactions:

  • reactions between metal & non-metal elements

(Ionic bonding / forms ionic compounds)


  • metal atoms loose electrons to form positive ions (anions)

  • non-metal atoms gain electrons to form negative ion (cations)


  • ions formed now have full (stable) outer shells


  • electrons are transferred ( from metals to non-metal)


  • oppositely charged ions attract each other so the bonds holding the ionic compound together are strong


    (hard to separate = not very reactive)


  • the ionic product formed is usually a solid



e.g. 2Mg(s) + O2(g) = 2MgO(s)

Molecular / Covalent Reactions:


  • reactions between non-metal & non-metal elements

(molecular bonding / forms molecular compounds)


  • bothe tyes of atoms (non-metals) need more electrons


    to gain full (stable) valence shells


  • electons are shares (between atoms)


  • bonds between the molecules are weak


    (so easily separated = more reactive)


  • molecular compounds may be liquid or gas



e.g. S(s) + O2(g) = SO2 (g)

some non- metals
can't exist on their own:


  • O2
  • H2
  • Cl2
  • I2
  • N2
    (S & C can exist on their own)

A decomposition reaction is a type of chemical reaction in witch a single compound breaks down into 2 or more simpler elements &/or compounds.


1 complex compound = 2 or more simpler elements &/or compounds


  • reactions often involve an energy source such as heat, light or electricity
    (but most reactions will occur slowly on there own in normal conditions)
  • decomposition reactions are exothermic

the tests:

the different tests:


The pop test
place a lit splint above the test tube. if the gas that is produced is hydrogen then you will hear a pop sound. this is becase the hydrogen explodes from the flame.
tests for - hydrogen gas (H+)


The limewater test
place the reactants in a test tube, pass the gas produced through a delivery tube into another test tube containing limewater (calcium hydroxide). the gas bubbles into the limewater and if the gas is CO2 then the limewaer will turn cloudy
testing for - Carbon Dioxide gas (CO2)


the glowing splint test
place a glowing splint (not lit) inside a test tube. if the gas produced in the reaction is oxegen then the glowing splint will re-light
testing for - oxygen gas (O2)


(testing if water is produced:)
If water vapour is produced in a reaction the gas (H2O) will condense when it reaches the cooler air at the top of the test tube, so small water droplets (condensation) can be viewed on the inside of the test tube

2 types of decomposition:

Thermal Decomposition:

Catalytic decomposition:

decomposition reactions
speed up by heating


  • require the reactant substances to be heated,
    in order for the decomposition to occur

3 types of compounds that undergo
decomposition by heating
carbonates
hydrogen carbonates hydroxides**


  • Carbonates & hydroxides of group 1 metals,
    don't decompose by heat (thermal decomposition)
    (all hydrogen carbonates decompose on heating)

Decomposition reactions speed up
by the addition of a Catalyst


Some substances can undergo decomposition without heating, they slowly undergo decomposition all on their own. However the reaction maybe sped up by the addition of another substance, called a Catalyst


Catalyst = A substance that increases the rate of reaction of a chemical reaction, without being used up in the reaction

3 types

Decomposition of Metal Carbonates by heat


  • metal carbonates, (that decompose) leave a residue of metal oxide & evolve a CO2 gas
    (the gas can be tested with the lime water test)

metal carbonate (heat) = metal oxide + carbon dioxide

Decomposition of Metal Hydroxides using heat:


  • leaves a residue of metal oxide & evolves H2O
    (the water will condense on the test tube)

Metal hydroxide (heat) = metal oxide + water


(some metal hydroxides decompose so easily that they can't be kept solid (easily) because they just decompose back into liquids)

Decomposition Metal Hydrogen Carbonates using heat


  • forms a metal carbonate & evolves a CO2 gas & H2O
    (can be tested with the limewater test, and
    if H2O is produced it will condence on test tube)

metal hydrogen carbonate (heat) = metal carbonate + carbon dioxide + water

How a Catalyst works:


1) Provide alternate reaction pathways, witch lower activation energy (now its easier)


2) Therefor, energy requirement for a successful collision resulting gin a reaction,decreases


3) The successful collisions rate of particles, increases


4) the Reaction Rate is faster


5) Products are formed more rapidly (e.g. bubble will form at the faster rate)

example of excellence answer:


When a catalyst is added to a solution it creates alternate reaction pathways so the activation energy required for the reaction decreases. this means the collisions of reactant particles don;t need as much energy to be successful. there is a greater number of successful collisions that form products, so the reaction rate increases. while the catalyst is involved with the reaction, by reducing the energy barrier, the substance is not used up in the reaction, and will remain after it is finished

Hydrogen Peroxide, decomposition reaction with a catalyst
Hydrogen Peroxide = H2O2(aq)


Hydrogen Peroxide is a substance that undergoes decomposition slowly at room temperature

  • water (H2O) & Oxygen gas (O2) are formed in this reaction (bubbles of oxygen gas are observed as the decomposition occurs + a glowing splint will re-light )

there are 2 catalysts that can assist with the reaction:


manganese Dioxide:

  • black powder stays black
  • fizzes rapidly
  • test tube heats up (exothermic)

Potassium Iodide:

  • white powder turns yellow/orange
    fizzes rapidly
  • test tube heats up (exothermic)