Energy and Fuels
Chemical reactions releasing energy
Exothermic!
Exothermic
•
•
•
•
Energy released is measured in joules (J)
Or Calories (1 cal = 4.2J) – hence ‘Calorimitry’
Q= mc Δ T
Q is energy transferred(J/g), m is mass of
water (g), c is ‘specific heat capacity’ of water
(J/goC) and Δ T is the temperature change
• Multiply Q by RAM and you know the energy
released in J/mol or kJ/mol
Calorimitry Issues
• Energy will be lost to the surroundings, so
most simple Calorimitry is wildly inaccurate!
Energy Changes in Reactions
• Just use the same equation! Q= mc Δ T
• Any reactions using liquids will be assumed to
behave like water. (SHC of 4.2 J/g)
• You will be given the information to plug into
an equation….
• You may have to do some working
Q
mc
ΔT
Where does the Energy come from? –
Bond Energy
• Bond Energy is the energy needed to
break/make a bond
• The difference in bond energy between
reactants and products shows us whether the
reaction is Exo or Endo thermic
Q1. Hydrogen could be the fuel used in all cars. One advantage is that when hydrogen
reacts with oxygen only water is produced.
The chemical equation for this reaction is:
2 H2 + O2
2H2O
This equation can be written showing the structural formulae.
2H―H +
O═O
2H―O―H
(a) Use the bond energies in the table to calculate the energy change for this reaction.
Bond
Bond Energy KJ
H―H
436
O═O
498
O―H
464
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Energy change = .............................................. kJ
Reactant Bond
Energy
EXOTHERMIC
Energy Released
Energy
Product Bond
Energy
Product Bond
Energy
Energy Required
Energy
Reactant Bond
Energy
ENDOTHERMIC
Strike a match?
Reactant Bond
Energy
EXOTHERMIC
Activation Energy
Energy
Energy Released
Product Bond
Energy
Catalytic Convertor
Reactant Bond
Energy
EXOTHERMIC
Activation Energy
lowered by a
catalyst
Energy
Energy Released
Product Bond
Energy
Polluted Water Supply
What…..
Positive Ions
• Flame tests
• Hydroxide Tests
Negative Ions
• Limewater test (carbonates)
• Nitric Acid / Silver Nitrate
test (Halides)
Ionic equations…
Ie Cu2+ (aq) +2OH- (aq)
Cu(OH)2(s)
How much…
Idea…
• If a known volume of a
know concentration of acid
is neutralised by a known
volume of an unknown
concentration of alkali, we
can work out the unknown
concentration
• This means we need a very
precise indicator
Concentration
• mol/dm3
mol dm-3
• dm3=10x10x10=1000 cm3=1000ml=1litre!
mol
Conc. Vol.
So…
How Much….
(b) The acid in 25.0 cm3 of the champagne reacted completely with 13.5 cm3 of
sodium hydroxide of concentration 0.10 moles per cubic decimetre.
Calculate the concentration in moles per cubic decimetre of acid in the champagne.
Assume that 1 mole of sodium hydroxide reacts completely with 1 mole of acid.
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Concentration = ......................... moles per cubic decimetre
Key info in question…
(b) The acid in 25.0 cm3 of the champagne reacted completely with 13.5 cm3 of
sodium hydroxide of concentration 0.10 moles per cubic decimetre.
Calculate the concentration in moles per cubic decimetre of acid in the champagne.
Assume that 1 mole of sodium hydroxide reacts completely with 1 mole of acid.
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Concentration = ......................... moles per cubic decimetre
Working
1. 1 mol NaOH to 1 mol acid
2. If we know number of
mols of NaOH, we know
the number of mols of
acid
3. We have 13.5cm3 of NaOH
at a conc. of 0.10mol per
dm3 (1000cm3)
4. 0.10/1000 = 0.0001 mol in
1cm3
5. 0.0001 x 13.5 = 0.00135
mol NaOH in total
1. If we have 0.00135 mol
NaOH, we have 0.00135
mol acid also.
2. Volume is 25cm3
3. So, 0.00135/25=
0.000054 mol in 1cm3
4. 0.0054 x 1000 =
0.054 mol dm-3
Order
• Conc of substance 1 in
mol dm-3
• Number of mol in 1cm3
(conc/volume)
• multiply number of mol
by volume to give mol
in known volume
• Find ratio of one
substance to the other
• Use ratio to find
number of mol in
substance 2
• Divide number of mol
by volume to get mol in
1cm3
• Multiply number of mol
by 1000 to get mol dm-3
of substance 2!
What next…
• Internet research to
complete the analysis
sheet you have been
given
• Use this presentation to
complete the questions
in your booster booklet
Remember focus on the skills in rearranging equations to work out titrations
Don’t worry too much about why
This is one small section of C3!