Chemical Reactions and the
Periodic table
Classifying the elements
Stoichiometry
(2)
Construct and use word equations.
• http://www.acceleratedstudynotes.com/2012/02/04/igcsecoordinated-science-stoichiometry/
• http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_
pre_2011/periodic_table/chemicalequationsrev1.shtml
• See example below
Word equations
• A chemical equation tells you which chemicals
reacted together (the reactants) and the new
chemicals that were made in the reaction (the
products).
• The simplest equation is a word equation. For
example:
• sodium + chlorine → sodium chloride
• http://misterguch.brinkster.net/PRA018.pdf
Construct and use symbolic equations with
state symbols, including ionic equations
• http://www.onlinemathlearning.com/ionicequation.html
Write the ionic equation for the word equation
Sodium chloride(aq) + silver nitrate(aq) → silver
chloride(s) + sodium nitrate(aq)
• Step 1: Write the equation and balance it if necessary
• NaCl(aq) + AgNO3(aq) → AgCl(s) + NaNO3(aq)
• Step 2: Split the ions. (Only compounds that are aqueous
are split into ions.)
• Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq) → AgCl(s) + Na+(aq)
+ NO3• Step 3: Cancel out spectator ions. (Spectator ions are ions
that remain the same in their original states before and
after a chemical reaction.)
• Step 4: Write a balanced ionic equation
• Ag+(aq) + Cl-(aq) → AgCl(s)
Equations to balance and answers
• ___ NaNO3 + ___ PbO —->___ Pb(NO3)2 + ___ Na2O
• 2NaNO3 + 1PbO —-> 1Pb(NO3)2 + 1Na2O
• Both sides of the equation has the same numbers of
atoms of each element: 2Na; 2NO3; Pb; O
•
•
•
•
•
•
___ AgI + ___ Fe2(CO3)3 —-> ___ FeI3 + ___ Ag2CO3
6 AgI + Fe2(CO3)3 —-> 2FeI3 + 3Ag2CO3
___ C2H4O2 + ___ O2 —–> ___ CO2 + ___ H2O
C2H4O2 + 3O2 —–> 2CO2 + 2H2O
___ ZnSO4 + ___ Li2CO3 —-> ___ ZnCO3 + ___ Li2SO4
ZnSO4 + Li2CO3 —-> ZnCO3 + Li2SO4
Energy changes in chemical
reactions
Types of Chemical reactions
Deduce the balanced equation for a chemical
reaction, given relevant information
• You will need to practise this using your text
book and some of these websites.
• Remember you’ll not get really hard examples
and you’ll only need to do it if you’re doing
higher tier.
Redox reactions
http://www.chemguide.co.uk/inorga
nic/redox/definitions.html
Define oxidation and reduction in terms of oxygen loss/gain, and
identify such reactions from given information
• Oxidation is gain of oxygen.
• Reduction is loss of oxygen
• Oxidation is loss of hydrogen.
• Reduction is gain of hydrogen.
.
Define redox in terms of electron transfer, and
identify such reactions from given information
• Oxidation is loss of electrons.
• Reduction is gain of electrons.
Energetics of a reaction
Relate the terms exothermic and endothermic to the
temperature changes observed during chemical
reactions
• http://www.chemguide.co.uk/physical/energe
tics/basic.html
• A reaction in which heat energy is given off is
said to be exothermic.
• A reaction in which heat energy is absorbed is
said to be endothermic.
• You can show this on simple energy diagrams
For an exothermic change:
• Notice that in an
exothermic change,
the products have a
lower energy than
the reactants.
• The energy that
the system loses is
given out as heat.
• The surroundings
warm up.
For an endothermic change
• This time the
products have a
higher energy than
the reactants.
• The system
absorbs this extra
energy as heat
from the
surroundings.
Demonstrate understanding that exothermic and endothermic
changes relate to the transformation of chemical energy to
heat (thermal energy), and vice versa.
• Chemical energy is transformed to heat
energy in an exothermic reaction
• And heat energy is transformed to chemical
energy in an endothermic reaction
• Endothermic change
Exothermic change
Speed of reaction
http://www.docbrown.info/page03/3
_31rates.htm#3e
Collision theory and rates of reaction
• For a chemical reaction to occur, the reactant
particles must collide.
• But collisions with too little energy do not produce
a reaction.
• The particles must have enough energy for the
collision to be successful in producing a reaction.
• The rate of reaction depends on the rate of
successful collisions between reactant particles.
• The more successful collisions there are, the faster
the rate of reaction
•
http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gateway_pre_2011/rock
s_metals/7_faster_slower1.shtml
• There’s an animation on this site
Describe the effect of concentration, particle size,
catalysis and temperature on the speeds of reactions.
• The rate of a chemical reaction can be
increased by raising the temperature.
• It can also be increased by increasing the
concentration of a reactant in solution,
• or the pressure of a reactant gas
• Or changing the particle size of a solid
reactant
• Catalysts also increase the rate of reaction
Changing the temperature
•
•
•
•
If the temperature is increased:
the reactant particles move more quickly
they have more energy
the particles collide more often, and more of
the collisions result in a reaction
• the rate of reaction increases
Changing the concentration or
pressure (if reactant is a gas)
• If the concentration of a dissolved reactant is
increased, or the pressure of a reacting gas is
increased:
• the reactant particles become more crowded
• there is a greater chance of the particles
colliding
• the rate of reaction increases
Changing the surface area
• If a solid reactant is broken into small pieces
or ground into a powder:
• its surface area increases
• more particles are exposed to the other
reactant
• there are more collisions
• the rate of reaction increases
Graphical representation
• Higher temperature and higher
concentration increases the rate
• Lumps react more slowly than powders
Define catalyst as an agent which increases rate
but which remains unchanged.
• A catalyst is a substance that can increase the
rate of a reaction.
• The catalyst itself remains unchanged at the
end of the reaction it catalyses.
• Only a very small amount of catalyst is needed
to increase the rate of reaction between large
amounts of reactants.
• They are specific, ie different catalysts catalyse
different reactions.
Some common catalysts used in industry and
the reactions they catalyse
catalyst
reaction catalysed
making ammonia
iron
from nitrogen and
hydrogen
making nitric acid
platinum
from ammonia
making sulphuric
vanadium(V) oxide
acid
Describe a practical method for investigating the
speed of a reaction involving gas evolution
• Measuring the
production of a gas
using a gas syringe
• eg this could be the
reaction between
marble chips and
Hydrochloric acid
•
http://www.bbc.co.uk/schools/gcsebitesize/science/ocr_gate
way_pre_2011/rocks_metals/7_faster_slower2.shtml
Devise a suitable method for investigating the effect
of a given variable on the speed of a reaction
• You could investigate the effect of changing
the concentration of the acid in the previous
experiment.
• You an measure the volume of gas released
every 2 minutes.
• This will give you a measure of the rate
Interpret data obtained from experiments
concerned with speed of reaction
• The faster the rate, the more reactant is used,
or product is made, in a given time.
• The faster the reaction, the steeper the line on a
graph showing total product against time will
be.
• A reaction finishes when one of the reactants is
all used up.
• No more product is made, so the line on a graph
of total product against time will become
horizontal.
• The rate can be calculated using this equation:
• rate of reaction = total amount of reactant used or
product made ÷ time taken
• What is the rate of reaction if 24cm3 of hydrogen
gas is produced in two minutes?
• rate of reaction = 24 ÷ 2 = 12 cm3 hydrogen / min
Describe and explain the effects of temperature and
concentration in terms of collisions between reacting particles
(concept of activation energy will not be examined).
• When gases or liquids are heated the particles
gain kinetic energy and move faster (see
diagrams on next slide).
• The increased speed increases the chance
(frequency) of collision between reactant
molecules and the rate increases.
• Increasing the concentration, increases the
probability of a collision between reactant
particles
• There are more of them in the same volume and
so this increases the chance of a fruitful collision
forming products.
http://www.docbrown.info/page03/3_31rates.htm#3e
Describe the application of the above factors to the danger of
explosive combustion with fine powders (e.g. flour mills) and
gases (e.g. mines).
• Explosions
• Explosions are very fast reactions in which a lot
of gaseous product is released very quickly.
• Fine powders can cause explosions - for
example, coal dust, custard powder, flour or
sulphur.
• This is a particular hazard in factories and mines
• Great care is needed to avoid naked flames or
other sources of ignition.